Konsummotive bei Konsumenten von amphetaminartigen Substanzen (ATS)

Mapping techniques are frequently used in learning research, but their application in a clinical setup is largely unexplored. The goal of this study, therefore, was to investigate whether mind maps can be used in the diagnosis of use motives of amphetamine type stimulants and whether these motives can be attributed to the four motive dimensions enhancement, social, coping and conformity common in use motive research. In addition, the motive distribution was analyzed with respect to the time period of use (first vs. latest month of use) as well as differences between subgroups. Descriptive analyses of the mind maps gave information about the most frequently named use motives. Method. A category system based on the four motive dimensions was developed by means of qualitative content analysis. Six independent

Ausgehend von der Tatsache, dass der DMQ-R (Drinking Motive Questionnaire Revised) und dessen Kurzform (DMQ-R SF) Trinkmotive zuverlässig und valide misst ( (1). ATS use is particularly common between the ages of 20 and 40 (7,8) with men being more frequently ATS dependent than women (7). Recent research has investigated a number of ATS-related issues including the illicit use of prescription stimulants (9)(10)(11) and the influence of expectancies of stimulant use on cognitive enhancement and the initiation and maintenance of substance use (12)(13)(14). Treatment demand has been persistently high since 2003 (1) illustrating the need for effective prevention strategies and treatment measures.
To this end, a profound understanding of the motives for ATS use is required. Exploratory studies have made important first steps in this direction but have been restricted by small samples or qualitative data, making a generalization of the results difficult. Milin et al. (15) investigated different motives of ATS use in outpatient and inpatient settings, albeit without a theoretical basis. They found the motives "I like the effect, " "craving, " "enjoying leisure time, " "mood improvement, " and "going out despite exhaustion" were the most highly rated. Due to the lack of a theoretical model, it however remains difficult to deduce clear recommendations for prevention or treatment strategies. Further studies dealing with ATS use have provided, amongst others, motives such as enhancing sexual performance (15)(16)(17), improving (cognitive) performance, performing better or enhancing the efficiency of an action (10,(17)(18)(19)(20)(21) and losing weight (15,17). For persons with attention deficit hyperactivity disorder (ADHD), stimulants cause in addition often paradoxical effects such as calming down and an improved ability to focus on activities (22) and can to some extent be regarded as negatively reinforcing by reducing stressful effects of their activities, tasks and requirements. Other theory-based studies investigated use motives based on the Motivational Model of Alcohol Use (23,24) for MDMA use (25) and for substance use of psychotic patients (24). To the best of our knowledge, to date there are no instruments that assess the motives for ATS use in a valid and reliable way which are based on a theoretical model. Such an instrument, however, is essential in generating targeted preventive and therapeutic treatments (26)(27)(28).
The theoretical framework developed in the Motivational Model of Alcohol Use (23, 29) is a promising approach for classifying the motives for ATS use from a theory-guided emotionalchange perspective and laying a foundation for preventative and therapeutic treatments. According to this two-dimensional model, people display certain behaviors in order to achieve a desired affective change (30). This represents the first dimension, valence, with positive reinforcement (i.e., to increase positive feelings) or negative reinforcement (i.e., to decrease negative feelings). The second dimension consists in the source of the affective change which can be internal or external. The crossing of the two dimensions results in the four broad motive categories enhancement, coping, social, and conformity shown in Table 1.
While originally developed for alcohol use, adaptions of the Motivational Model were successfully transferred to other domains of human functioning such as gambling [GMQ (31)], sexual risk-taking behavior (32), Internet use [IMQ-A (33)], and listening to music [MLMQ (34)]. In the same vein, this article aims to develop a questionnaire to assess motives for using illicit ATS-the Amphetamine-type stimulants Motive Questionnaire (AMQ).
Based on Cox and Klinger's Motivational Model (23,30,35), the Drinking Motive Questionnaire Revised (DMQ-R) was developed which was later published in a short version [DMQ-R SF (36)]. We decided to use the short form of this questionnaire as the basis for the development of the AMQ as it performs very similarly to the longer version DMQ-R (36, 37) but is more viable in a clinical setting. To this end, we adapted the phrasing of the 12 items of the DMQ-R SF to ATS use and converted them into the first person, e.g., "…because you like the feeling" was modified to "…because I like the feeling. " Recent research (15,38) and clinical observations have provided indications for differences between motives at the beginning of ATS use and after the development of ATS dependence. Therefore, we studied the motives in the first and latest month of ATS use unlike other studies which usually investigate the motives for other behaviors such as alcohol use (32,36) during the last twelve months. However, in both cases the formulation of all items remained the same as in the DMQ-R SF.
The following hypotheses were tested: (a) For both periods of time, we predicted a good fit of the AMQ four-factor model and high factor loadings of the corresponding items, and at least satisfactory internal consistencies, which provide evidence for construct validity (39,40). (b) We also predicted, for both periods of time, equivalence of the factor structure among subgroups (gender and age) in respect to the four-dimensional factor structure of the AMQ which is a pre-requirement for group comparisons. (c) Furthermore, we tested mean differences in the subgroups gender and age in the four factors for both periods of time. Based on previous research (38), we expected a higher level of coping motives for women than men. Moreover, we also explored age differences in ATS use motives (due to non-existing evidence in previous studies). (d) Finally, we estimated a multivariate structural equation model to confirm the concurrent validity. Clinical observations and results in the field of alcohol and cannabis use motives (24) have suggested that the use frequency of ATS use (for the first and the latest month of use) is associated with coping and enhancement motives.

MaTerials anD MeThODs study Design
We collected data from individuals with ATS disorders who presented as outpatients at drug counseling centers or as inpatients in hospital based drug treatment programs. Of the 133, 11 contacted drug-counseling centers (participation rate: 8.3%), 1 of the 13 contacted cessation therapy clinics specialized in crystal meth addiction (participation rate: 7.7%), 2 contacted addiction departments, and 1 forensic department of Regional Psychiatric Hospitals took part in the study. The Ethics Council of the University of Bamberg granted permission to conduct the study (July 28, 2014/June 06, 2016). Only patients who were primarily addicted to illicit ATS were asked whether they were interested in participating in the study. The patients were briefed on the goals and contents and were informed about their right to withdraw from the study at any time. Participation was voluntary for all patients and anonymity was guaranteed. The participants were asked to complete questionnaires on their ATS use motives (AMQ), patterns of ATS use and demographic data. All outpatients received a 5€ remuneration for taking part in the study. The data were collected between January 2015 and July 2016.

sample and Missing Values
The original sample consisted of 248 individuals with ATS disorders. Participants who did not use ATS as their primary drug of choice (N = 8, 3.2%) were excluded as were those who failed to answer more than half of the questions on ATS use motives (N = 6, 2.4%) and one participant who took part in the study on two occasions (0.4%). The remaining data included 233 participants. There were no missing values on gender or age. The full information maximum likelihood (FIML) option of the statistical software AMOS (41) was used to account for the remaining missing values (up to 2.1% per item). The analyzed data consisted of 173 men (74.2%) and 60 women (25.8%). The mean age was 31.1 years (SD = 7.9; age range 18-54). Drug counseling centers provided 113 data sets (48.5%), 49 data sets (21.0%) were provided by addiction departments of Regional Psychiatric Hospitals, 43 (18.5%) by a cessation therapy clinic, and 28 (12.0%) by a forensic department of a Regional Psychiatric Hospital.

Measures
The 12 motive items in the AMQ were adapted from the DMQ-R SF (36) with 3 items per dimension (enhancement, social, coping, and conformity). As the use motives seem to differ between the beginning of ATS use and, e.g., after the development of an ATS addiction (15,38) the participants were asked to specify how often they used ATS for two periods of time: in their first month of use and their latest month of use. Possible answers were "never" (coded as 1), "seldom" (coded as 2), "sometimes" (coded as 3), "most of the time" (coded as 4), and "always" (coded as 5). The phrasing of all items is given in Table 2.
The patient questionnaire is based on the "Deutscher Kerndatensatz Klienten (KDS-K) zur Dokumentation im Bereich der Suchtkrankenhilfe" (German core data set of clients for documentation in the field of addiction treatment) (42) which has been applied in German drug-counseling centers and in inpatient drug treatment centers since 2007. It provides, amongst others, information about the age, gender (1 = female, 2 = male) and frequency of use in the first and the latest month of use, coded as monthly frequency, i.e., several times a day = 60, once a day = 30, three to six times a week = 19, one to two times a week = 6, two to three times a month = 3, once a month = 1, and less than once a month = 0.

statistical analysis
We used confirmatory factor analysis (CFA) estimated in statistical software SPSS (AMOS Version 23), in order to confirm the assumed four-factor structure of the AMQ (a) for ATS use in the first month and ATS use in the latest month, separately. Since the formulation of two item pairs was more similar than the third item used to constitute a given latent factor (e.g., the two items "to get high" and "because it's fun" as enhancement motives) the errors of the two item pairs were allowed to correlate as to compensate answer tendencies (43 (40).
To test the equivalence of the factor structure in different subgroups (b), we estimated nested models of confirmatory factor analyses with increasing constraints for gender and age (median split: younger users up to 30 years vs. older users over 30 years). First, we tested the configural invariance for the grouping variables gender and age which is supported if the unconstrained model has an acceptable fit to the data. Second, we tested the metric invariance for the grouping variables which requires equivalent factor loadings between the groups (λ-constrained model). Furthermore, we analyzed whether the fit indices remained equivalent when we constrained the variances in addition to the factor loadings (third model) and, finally, when we constrained the factor loadings, the variances and the correlations between the groups (fourth model) (43,45). We compared the CFI, the TLI and the RMSEA of the fixed models with the fit indices of the freely estimated models.
Furthermore, independent sample t-tests conducted in SPSS 23 were used to test mean differences in the motive dimensions (c) between the gender and age subgroups. Therefore, we computed mean scores for the four motive dimensions.
To confirm the concurrent validity (d), we estimated a structural equation model with the latent four motive factors as independent variables and the ATS use frequencies of the first and the latest months of use as dependent variables. All analyses were conducted with SPSS AMOS Version 23 (41) by using the FIML option of AMOS. resUlTs confirming construct Validity of the aMQ For the first month of ATS use, the CFA provided highly significant factor loadings reaching from 0.48 to 0.95 (all p < 0.001; Table 2). The social factor had the lowest and the highest item loadings. The conformity factor had consistently high item loadings from λ = 0.71 to λ = 0.85 with an internal consistency of 0.85. All other internal consistencies were 0.72 or higher. Except between enhancement and social, all interfactor correlations were smaller than 0.20. There was a good fit to the data with a CFI of 0.945, a TLI of 0.907, and a RMSEA of 0.071.
The CFA of the latest month of use also provided highly significant factor loadings (all p < 0.001; Table 2) reaching from 0.54 to 0.88. The enhancement factor had the lowest item loading (λ = 0.54) with an internal consistency of α = 0.72. The highest item loading was found on the social factor (0.88), its internal consistency was α = 0.84. As in the first month of use, we observed the highest correlation between the enhancement and the social factor; all others were smaller. There was a good fit to the data with a CFI of 0.940, a TLI of 0.898 and a RMSEA of 0.077.

Testing construct Validity in Different subgroups
In order to test the four-factor structure of the four-factor model according to gender and age groups, we performed nested models of confirmatory factor analyses with increasing degrees of freedom for the subgroups. For the first month of ATS use configural invariance was given for all subgroups (unconstrained models) with CFI and TLI values above 0.9 and RMSEA below 0.1 ( Table 3). Metric invariance was also given as the model fit only differs slightly between the unconstrained and λ-constrained models. Furthermore, the fit indices in the two subgroups did not change considerably when we constrained the factor loadings and variances (third model), or the factor loadings, variances and  correlations (fourth model). All CFI and TLI values were above 0.9 and all RMSEA values below 0.1. For the latest month of ATS use, configural invariance was given in the unconstrained model for the subgroup gender with CFI and TLI values above 0.9 and RMSEA below 0.1 and almost given for the subgroup age with a CFI value of 0.935, a TLI value of 0.890, and RMSEA below 0.1. All other tested models (λ-constrained model, plus variance constrained model, and plus correlations constrained model) displayed similar CFI values above 0.9, TLI values very close to 0.9, and RMSEA values below 0.1 in both subgroups gender and age ( Table 3).
The results basically remained the same when the sample was split at age 25 and 35, respectively. The resulting model fit indices can be obtained from the authors on request.

Testing Mean Differences between the subgroups
In the first month of ATS use, men scored higher on positive reinforcement (enhancement and social motives). However, this difference was only significant for enhancement motives ( Table 4). Women scored somewhat higher on negative reinforcement (coping and conformity motives) but the differences were not statistically significant. The subgroup age revealed no significant differences in the four motive dimensions. Younger ATS users scored slightly higher on enhancement, social, and conformity motives and lower in coping motives than older ATS users but none of these differences were significant.
In the latest month of use, men scored higher on positive reinforcement (enhancement and social motives) and on conformity motives with a significant difference in enhancement motives ( Table 4). Women and men scored identically on coping motives.
Also for the latest month of ATS use, the subgroup age revealed no significant differences in the four motive dimensions.

confirming concurrent Validity of the aMQ
The estimation of the structural equation model revealed that higher coping motives are connected with higher frequency of ATS use for the first and the latest month of ATS use. A further positive association was found between social motives and frequency of ATS use for the latest month of use ( Table 5). The explained variance was 12.6 and 15.6% for the first and the latest month of ATS use, respectively. In a final step, the link between the four motive factors and frequency of ATS use was adjusted for gender and age effects. However, the results (not shown but available from the authors on request) remained basically unchanged due to non-significant gender and age effects.

DiscUssiOn
The aim of this study was to develop the four-dimensional AMQ and to validate it with regards to the first month and the latest month of ATS use. It was expected that the AMQ and its underlying theoretical considerations are valid for both periods of time which was formally tested in this article.
The first aim (a) was to test construct validity (39) by means of CFA which revealed good model fit according to the CFI and the RMSEA values and acceptable model fit according to the TLI values for the hypothesized four-factor model for motives of ATS use. The values for the recall of the first month of ATS use were consistently slightly higher in terms of factor loadings of the corresponding items which means that the data gathered for Frontiers in Psychiatry | www.frontiersin.org September 2017 | Volume 8 | Article 183 the first period of time was slightly better approximated by the four-factor model. The highest interfactor correlation was found between social and enhancement for both periods of time with slightly higher values for the recall of the latest month of use. This indicates that those who used ATS for instance "because it is fun" also tended to use it because it improves parties and celebrations. This relation may become even more important over time. A strong link between enhancement and social motives was also found for alcohol use (32,36) and listening to music (34). Furthermore, consistent with previous research on other domains of human functioning, high internal consistencies were found for both periods of time (40) which is particularly remarkable considering only three items were used to measure each factor. Second (b), the CFA in the subgroups demonstrated the equivalence of the four-dimensional factor structure of the AMQ across gender and age. This not only indicates that the theoretical assumptions held true in both subgroups but also that the AMQ can be used to compare both subgroups. Based on the different scores in the motive dimensions, subgroup-specific interventions may be deduced for clinical practice.
The analysis of mean differences across subgroups (c) revealed that men use ATS more frequently due to enhancement motives than women. This was true for both periods of time. A possible explanation is that men are generally more open to new experiences, seek extreme sensations, and are more willing to experience adverse consequences (46,47). No gender-specific differences were observed at either period of time in any other motive dimension. The expected differences in the coping dimension could not be confirmed, which may be explained by the fact that our study includes a different selection of items than the cited study (38). There were no significant age differences in the four motive dimensions for either period of time. Therefore, motive based therapies may be applied to a wide age range.
The questionnaire was found to have concurrent validity (d) as the structural equation model revealed a significant positive relation between coping motives and frequency of use in the first and latest month of ATS use, i.e., those who used ATS to cope used them more frequently. This is to some extent consistent with previous research (24) in which the frequency of ATS use was associated with coping and enhancement motives and underlines the vicious circle in which patients with ATS disorders often end up: coping with problems caused by using ATS leads to further ATS use. Furthermore, there was a significant positive relation between social motives and frequency of use in the latest month of ATS use, i.e., those who used ATS for social reasons in this time period used them more frequently. This may be related to the circle of acquaintances the users have built and with whom they party regularly.

limitations and recommendations for Future research
Since the study relies on the retrospective recall of use motives, memory bias constitutes an important limitation (48) which may partly explain the sufficient but not optimal model fit.
The sample consisted of a heterogeneous group of patients which differed in the length of their abstinence: some presented themselves at drug counseling centers and were not abstinent at that time, some were in cessation therapy clinics and were abstinent from 0 to 6 months and others again were in the forensic department of a Regional Psychiatric Hospital and were abstinent from a few months to a few years. Depending on the recency of their last ATS use (49-51) and history of treatments (52), patients had different opportunities to deal with their relapses, to develop abstinence skills and to reflect on their motives of ATS use. Particularly the latter aspect may have had an effect on the answers given in the questionnaire. While mean levels of motive endorsement may be subject to recall bias, the four-factor classification of motives according to the valence and the source is not affected as studies in the field of alcohol use have shown (37,45). We, thus, consider the recall bias as reasonable trade-off between feasibility of data collection and accuracy. In addition, some important aspects in the field of ATS use had not been considered in the 12-item AMQ: individuals with ATS disorders reported using ATS to improve sex (15)(16)(17), to enhance their cognitive performance (10,(17)(18)(19)(20)(21), to lose weight (17), to be able to stay awake, and as a self-medication (22) for symptoms of ADHD. Although the aforementioned reasons seem to be less common compared to items in the AMQ such as getting high or having fun (17), further studies should examine the importance of other amphetamine-specific motives of ATS use. Considering the intricate circumstances in this clinical setting-e.g., approaching ATS users and convincing therapists of the advantages of participating in the study-the sample size of 233 people can be regarded as sufficient. Larger sizes of clinical samples are difficult to achieve. This becomes apparent in the generally low response rates reported in the study design section which may have had an effect on the results. Moreover, it should be examined whether the AMQ, which was developed and validated in this study using a clinical sample in Southern Germany, can also be applied to non-clinical samples and in other countries. It would also be worthwhile to apply the AMQ to primary substances like illicit prescription stimulants or MDMA and related drugs. Furthermore, longitudinal studies are needed to be able to prospectively evaluate the development of ATS motives over time. Finally, we recommend including additional outcome variables in future research to extend the concurrent validity of the AMQ.

conclusion
The application of the Motivational Model of Alcohol Use (23,29) to ATS use is an important step toward a better understanding of why people use ATS particularly since most use the substance in spite of knowing the high potential for dependence and the multiple somatic and mental consequences (2)(3)(4)(5)(6). Moreover, as a theory-based instrument, the AMQ closes a gap in ATS research and may assist in generating targeted preventive and therapeutic treatments (26)(27)(28) as it can reveal recalled former and current motives of ATS use. For the assessment of use motives of patients, the AMQ can help understand why people begin and continue to use ATS and in a second step to personalize the treatment which has to manage the resulting changes related to ATS abstinence Frontiers in Psychiatry | www.frontiersin.org September 2017 | Volume 8 | Article 183 (17). In this study, the AMQ was shown to be succinct and viable in a clinical setting and has demonstrated its construct validity and reliability. It also constitutes a basis for future research, in particular to study changes in the motive structure between the first and latest month of ATS use.

eThics sTaTeMenT
This study was carried out in accordance with the recommendations of the Ethics Council of the University of Bamberg with written informed consent from all subjects.

aUThOr cOnTribUTiOns
DT formulated the hypotheses, planned and scheduled the study (establishing cooperation with the participating institutions, raising funding), conducted the study (coordinating the gathering of data, acting as a contact person for the participating institutions), analyzed the results statistically, and wrote the article. EK formulated the hypotheses, planned the study, analyzed the results statistically, and wrote the article. JWe formulated the hypotheses, planned the study (establishing cooperation with the participating institutions), conducted the study (acting as a contact person for the participating institutions), analyzed the results statistically, and wrote the article. JWo formulated the hypotheses, planned the study (establishing cooperation with the participating institutions, raising funding), analyzed the results statistically, and wrote the article.

acKnOWleDgMenTs
The authors would like to thank the participants of the study for answering the questionnaires as well as the drug-counseling centers, the Regional Psychiatric Hospitals in Bayreuth and Erlangen, and the Hospital in Hochstadt for their collaboration and support in gathering the data.

Introduction
Worldwide, an estimated 34 million people aged from 15 to 64 years used amphetamine-type stimulants (ATS) [1]. ATS comprise amphetamine, methamphetamine, methcathinone, and ecstasy substances (3,4-methylenedioxymethamphetamine) [1]. Not only the high potential for addiction and physical harm of ATS [2,3] has been of increasing interest for clinical research but also the high comorbidity of substance use disorder (SUD) and attention-deficit/hyperactivity disorder (ADHD) [4][5][6]. ADHD is one of the frequent comorbid disorders of ear- ly-onset substance abuse [6,7] and found to be a significant predictor of SUD [5,7]. The abuse of ATS often leads to severe psychosocial and neuropsychiatric disabilities. The overlap of ADHD and SUD is associated with a greater severity, chronicity of addiction during lifetime, and a more frequent abuse than without ADHD [6,[8][9][10][11]. Individuals with ADHD are more likely to start consuming drugs at an earlier age, tend to polyvalent use of drugs, and have an increased risk of relapse compared to users without ADHD [12,13]. Furthermore, methamphetamine users with ADHD are more likely to be unemployed and report higher perceived levels of everyday functioning difficulties [14]. One of the largest international multicenter studies evaluating ADHD in SUD populations found 40.9% comorbid ADHD [4]. A meta-analysis by van Emmerik-van Oortmerssen et al. [15] showed an ADHD prevalence of 23% in substance abusing adults. Among chronic methamphetamine users, the prevalence of ADHD is 21% [14].
Considering the significance of the co-occurring of ADHD and ATS dependency and the lack of an evaluated and standardized treatment in this field [16], it is essential to identify the ATS use motives of patients with ADHD. For example, the self-medication hypothesis is often discussed as an explanation of why patients with ADHD tend to use ATS [17,18]. Thus, a profound understanding of motives could contribute to a better adaptation of clinical interventions and individual treatment options [19].
Substantial motives of various motivational-psychological questions, that is, for internet use [20], gambling [21], motivation for sex and risky sexual behavior [22], and listening to music [23], have been studied successfully. The motives for ATS use have also been examined with the Amphetamine-type stimulants Motive Questionnaire (AMQ; [24]).
The AMQ is based on an established short-form (DMQ-R SF; [25]) of the Drinking Motive Questionnaire Revised (DMQ-R; [26]), and it is theoretically derived from Cox and Klinger's motivational model of alcohol use [27]. The central idea of the motivational model (Table 1) is that whether people use alcohol or not depends on the expected outcome of their action. The first dimension contains the valence: expected positively affected consequences of consumption, that is, to increase positive feelings will outweigh reasons not to drink. However, negative consequences might be reduced due to negative reinforcement (i.e., to decrease negative feelings). Whether the affective change is external or internal is described on the second dimension of the model. Thus, the model contains 4 main categories of motives: enhancement, social, coping, and conformity motives. Based on recent research [24,28], we believe that the 4-factor model used in the AMQ can also be used to examine the ATS use motives of patients with ADHD.
Therefore, we used the following innovative mixedmethod approach: To measure use motives, we collected quantitative data via the AMQ [24] and qualitative data through mind maps [28]. According to the results, both the AMQ and the mind maps are helpful instruments for assessing motives of ATS use in a clinical population, which are needed to develop targeted preventive and therapeutic treatments and abstinence skills [19]. To date, no study has specifically examined the ATS use motives of adults with ADHD by using a mixed-method study approach.
Mapping techniques allow to visualize assumptions and concepts of a specific topic by noting a central term in the middle and associations connected to the central term around it. Mind mapping techniques have been long common in learning research, for example, as learning and teaching strategies [29] or as possibilities for knowledge diagnosis and modelling [30]. In a clinical setting, the survey of use motives is a promising application of mind maps.
Another novel approach in our study is that we ask for the use motives of the first and the latest month of ATS use. Recent research indicates that the use motives differ between the beginning of ATS use and, for instance, after the development of an ATS addiction [24,28,31]. In this study, we would like to approach the issue of the co-occurrence of ADHD and ATS dependency by examining the respective use motives.
The aims of the current study were as follows: First, to investigate the ATS use motives of adults with and without ADHD in the first and latest month of their use in a mixed-method approach, we used the AMQ (quantitative data) and a mind-mapping technique (qualitative data). To be able to do so, we examined whether the 4-factor model used in the AMQ is transferable to patients with ADHD and whether the mind-mapping technique leads to satisfactory inter-rater correlations. Second, we explored the qualitative data for additional use motives of patients with ADHD that might not be indicated by the AMQ.
The following hypotheses (a-e) were investigated: (a) For the first and the latest month of ATS use, we predicted a good fit of the AMQ 4-factor model for patients with ADHD. (b) We estimated the inter-rater reliability of the category system [28] for the patients with ADHD and expected a good value. (c) Based on previous research [18,24,28,32,33], we expected a higher level of enhancement motives in the first month of use and a higher level of coping and enhancement motives in the latest month of use for both the quantitative and qualitative data. (d) We also investigated further use motives for patients with ADHD within explorative analyses of the mind maps. Finally (e), we tested mean differences in the 4 factors for both periods of time for the quantitative and qualitative data and predicted, in line with the self-medication hypothesis [17,18], a higher level of coping motives for patients with ADHD.

Study Design
This study is part of the research project "Motives of Amphetamine-type Stimulants (ATS) Use," which was funded by the "Bayerische Akademie für Sucht-und Gesundheitsfragen (BAS)." From January 2015 to July 2016, we asked patients of 1 drug rehabilitation clinic specialized in crystal meth addiction, 1 addiction department, 1 forensic department of a regional psychiatric hospital, and several drug counseling centers to reflect on their use motives of ATS. They rated their use motives via a questionnaire (AMQ) for the first and latest month of their ATS use, completed questionnaires with demographic data, and gave further information on their ATS use history (e.g., begin of use, frequency of use, and amount per use). In addition, information on their ADHD history was collected. Furthermore, all inpatients were asked to develop mind maps for the first and latest month of their ATS use. The patients were informed about the content of the study and their right to withdraw at any time. The participation was voluntary and confidential. The patients have given their written informed consent.
Being primarily addicted to ATS (F15.2) was the only condition for patients to participate in the study. Further addiction-related diagnoses or other comorbidities were allowed. The patients were interviewed at the earliest after finishing the somatic withdrawal of ATS. The Ethics Council of the University of Bamberg granted permission to conduct the study (July 28, 2014/June 06, 2016).

Sample and Missing Values
In total, 233 patients took part in the study, whereby 39 of these participants (16.7%) had and 184 participants (79%) had not been diagnosed with ADHD in the past. Specification of diagnoses was missing in 10 participants (4.3%). Thirty-one of the 39 with an ADHD diagnosis were men (79.5%), while 8 were women (20.5%). Their mean age was 30.72 years (SD = 7.85, age range 19-51). All 233 participants completed the AMQ, while the 96 inpatients in this sample also developed mind maps of their ATS use motives for the first and the latest month of use. Twenty of these mind maps were developed by participants with an ADHD diagnosis and were analyzed qualitatively. The analyzed mind maps consisted of 18 men (90.0%) and 2 women (10.2%). The mean age was 30.8 years (SD = 7.78, age range .

Measures
The use motives are expected to differ between the beginning of ATS use and, for example, after the development of an ATS addiction. To explore these motives, we asked the participants to complete the AMQ (see online suppl. material; for all online suppl. material, see www.karger.com/doi/10.1159/000508871 and [24]) and to reflect on their use motives by developing mind maps for both their first and latest month of use. The instruction therefore was "Please write down the amphetamine-type substance which you have predominantly used last in the middle of the 2 sheets of paper [marked with 1 and 2, respectively]. For the first sheet, please ask yourself the question: Why have you taken amphetamine-type substances during the first month of your use or why have you started using the substance? Simply write down your reasons in keywords on the sheet of paper and connect them with your used substance that you have marked in the middle. For the second sheet, please ask yourself the question: Why have you taken the substance mentioned above during the latest month of your use or why couldn't you stop using it? Again, write down the reasons for your use in keywords and connect them with your used substance you have marked in the middle. You can note down as many keywords as come to your mind on both sheets." In addition, the patients gave information about their age, gender, and whether they were diagnosed with ADHD in the past by either a psychiatrist or a clinical psychologist. Participants who affirmed an ADHD diagnosis answered these additional questions on their ADHD history: age at the time of the ADHD diagnosis, specific medication, duration of the medical treatment, and stop of medical treatment (autonomous or recommended by a physician).

Statistical Analysis
Analyses of the AMQ Based on the results of Thurn et al. [24], we tested the equivalence of the 4-factor structure in the subgroup ADHD/NON-AD-HD for the first and the latest month of use by estimating nested models of confirmatory factor analyses with increasing constraints. First, we verified the configural invariance for the grouping variable ADHD/NON-ADHD, for which the fit indices of the unconstrained model have to be acceptable. For this grouping variable, we also tested the metric invariance which constrains the factor loadings between the groups to be equivalent (λ-constrained model). In a third and fourth step, we constrained, in addition, the variances and finally the correlation between the groups and studied whether the fit indices remained equivalent [34].
The comparative fit index (CFI), the Tucker-Lewis index (TLI), and the root mean square error of approximation (RMSEA) were compared between the fixed and freely estimated models. The tested model can be compared with a null or an independent model using the CFI and TLI, where values of ≥0.95 for both indices indicate a good model fit [35]. The RMSEA quantifies the mean deviation per degree of freedom of the recorded data from the model. RMSEA values of <0.1 are desirable [35]. Cronbach's alpha is used to assess the internal consistencies of the AMQ, with values of 0.7 being regarded as satisfactory, 0.8 as good, and 0.9 as excellent [36]. Mean differences in the motive dimensions between the ADHD subgroups were studied using independent sample t tests with the Bonferroni correction. To this end, mean scores for the 4 motive dimensions were calculated.

Analyses of the Mind Maps
The category system of Thurn and Wolstein [28] (online suppl. material) is also based on the 4 dimensions of the Cox and Klinger Model of Alcohol Use [27] and was found to be a good tool to assess use motives of ATS in a clinical setting. In this study, we estimated the inter-rater reliability by using the SPSS 25 and Hayes' [37] macro. Basis for this estimation was the classification of the named use motives through 6 independent raters. The reliability was determined by Krippendorff's alpha [38], which overcame the disadvantages of other coefficients (e.g., Cohen's kappa [39] and Cronbach's alpha [40]). Krippendorff's alpha can be applied regardless of the number of raters, levels of measurement, sample sizes, and presence or absence of missing values [38]. Reliability values of 0.7 are considered as satisfactory, 0.8 as good, and 0.9 as excellent [36].
Also for the data from the Mind Maps, we tested mean differences in the motive dimensions between the ADHD subgroups with independent sample t tests with the Bonferroni correction. Therefore, we calculated the means of the motive dimensions. Furthermore, we investigated the special use motives of patients with ADHD for both periods of time.

Construct Validity of the AMQ
We performed nested models of confirmatory factor analyses with increasing degrees of freedom for the sub-group to verify the factor structure of the 4-factor model in a sample with patients with ADHD. For the first month of ATS use, configural invariance can be seen as given for the ADHD subgroup (unconstrained models) with a CFI value above 0.9, a TLI value very close to 0.9, and an RMSEA value below 0.1 ( Table 2). The fit indices of the λ-constrained model (metric invariance; factor loadings constrained), the third model (factor loadings and variances constrained), and the fourth model (factor loadings, variances, and correlations constrained) differ only negligibly. For the latest month of ATS use, the results of the fit indices were very similar ( Table 2).

Inter-Rater Reliability of the Mind Maps
The agreement of the 6 independent raters in classifying the use motives of adults with ADHD lay at a Krippendorff's alpha of 0.86. The bootstrapping method shows that the probability that the real Krippendorff's alpha is below 0.80 is vanishingly small with 0.00%.

Use Motives in the First and Latest Month of Use
In the AMQ data, the patients with ADHD most fre- Therein, the results of the patients with ADHD were similar to those of the complete sample (Thurn et al. [24]).
In the mind maps, the patients with ADHD also named enhancement motives (M = 3.18; SD = 2.14) most fre-  were named rarely. Therein, these results were very close to those of the complete qualitative sample [28]. Tables 3 and 4 show the participants' 10 most named categories of the first and latest month of ATS use over the 4 motive dimensions. In the first month, they decided to use ATS almost exclusively because of enhancement motives. Particularly, fun/kick/rush/desire (as a part of "fixing the high") and curiosity/interest in the drug/appeal were important reasons for ATS use. Using ATS to cope with ADHD symptoms (M = 0.60; SD = 1.85) and to utilize it as a self-medication (M = 0.60; SD = 1.85) is only the fourth and fifth most named reasons within the coping motives.

Explorative Analyses of the Qualitative Data (Mind Maps)
In the latest month of use, particularly, coping motives like repression, freeing the mind/not having to think/ switching off, coping with the dependency syndrome, and coping with the internal unrest/tension/anxiety were named. Reasons like coping with ADHD symptoms (M = 0.30; SD = 1.34) and using as a self-medication (M = 0.00; SD = 0.00) were named in very few cases. ATS, amphetamine-type stimulants.

Mean Differences in the Subgroup ADHD
The AMQ data show that, although patients with ADHD scored higher on coping motives in the first month of use, there were no significant differences between patients with ADHD and those without this diagnosis. This is valid for all motive dimensions and for both periods of time ( Table 5).
The results of the mind map analyses show that in the latest month of ATS use, patients with ADHD scored significantly lower on social motives. However, there were no other significant differences found between patients with and without ADHD for all motive dimensions and both periods of time (Table 6).

Discussion
The aim of this study was to investigate ATS use motives of adults with ADHD in the first and latest month of use as well as possible differences to adults without ADHD within a mixed-method approach. In addition, the qualitative data were explored with respect to other and/or additional use motives than the AMQ can identify.
We verified (hypothesis a) the equivalence of the 4-dimensional factor structure of the AMQ for patients with ADHD for both periods of time (Table 2). Thus, the AMQ can be used to compare patients with and without ADHD in addition to the subgroups gender and age [24] and can be regarded as a basis for subgroup-specific interventions.
Within the analyses of the mind maps, we proved a very good inter-rater reliability of 0.86 (hypothesis b) of the category system for the sample with ADHD via ratings of 6 independent raters. It is, thus, only marginally smaller than the inter-rater reliability of the complete sample [28]. The category system seems to be a reliable tool to ask for the ATS use motives of adults with ADHD.
The analyses of the use motives for the first and latest month of ATS use (hypothesis c) yielded the expected results [18,24,28,32,33], as found in the entire sample [24]. In both the quantitative and qualitative data, enhancement motives were the most important motives in the  first month of use. After that, coping motives became considerably more important. The analyses of the quantitative data suggest an equal importance of the coping and enhancement motives, and the analyses of the qualitative data suggest a greater importance of the coping motives in the latest month of use. Furthermore (hypothesis d), the analyses of the mind maps showed that in the first month of use, 8 of the 10 most named use motives were enhancement motives (Table 3). Particularly, motives like fun/kick/rush/desire and curiosity/interest in the drug/appeal were named often as reasons why they began to use ATS, which is in line with the results of the complete qualitative sample [28]. At that time, the enhancing effects presumably outweigh symptoms of a commencing dependency with its increasing physical harm [2,3]. In this, patients with ADHD do not differ from those without ADHD with respect to their use motives. The motives using ATS to cope with ADHD symptoms and utilizing ATS as a selfmedication were only in fourth and fifth place, respectively, among the most often named coping motives. Consequently, the treatment for both patients with and without ADHD has to focus primarily on the enhancing motives and their influence on the patients' decisions and actions when they get treatment in an early phase of ATS use.
In the latest month of use (Table 4), the most often named use motive is repression, which is also in agreement with the results of the complete sample [24,28]. In addition, use motives like freeing the mind/not having to think/switching off, coping with the dependency syndrome, and a lack of drive are mentioned very often. Reasons like coping with ADHD symptoms and using it as a self-medication were only named in rare cases. This implies that patients with ADHD do not differ strongly from patients without ADHD with respect to their use motives in the latest month of use and, thus, need treatment focused on the general coping motives mentioned above. Another reason for this result could be associated with the cognitive deficits of patients with ADHD (e.g., limited mentalization abilities in sense of low self-reflectivity, underestimation of ADHD-related impairments, and difficulties in linking actual impairment with ADHD) [41]. Over time, users become dependent on ATS, are affected by its accompanying physical harm [2,3], and have to deal with massive impairments. These impairments lead in turn to ATS use and a vicious circle develops including withdrawal symptoms (e.g., sleeping disorder, mood fluctuations, tense and depressive mood, and suicidal tendency) and frequent relapses. People no longer use ATS out of enhancement motives but rather of coping motives, for example, to reduce withdrawal symptoms [28]. According to our findings, patients with ADHD named a bigger variety of coping motives than patients in the complete sample [24], which reflects the recent findings regarding the relationship of ADHD and SUD with a greater severity, chronicity of addiction during lifetime, and a more frequent abuse in the ADHD population [6,[8][9][10][11].
The analysis of mean differences (hypothesis e, Tables 5, 6) between adults with and without ADHD revealed no significant differences for the quantitative and qualitative data at either period of time in the motive dimensions enhancement, coping and conformity. The expected significant differences in the coping dimension, which would have been in line with the self-medication hypothesis [17,18], could not be confirmed. One reason for this result could be that the items of the AMQs coping dimension ("… because it helps when I feel depressed or nervous.", "… to cheer up when I am in a bad mood.", and "… to forget about my problems.") only partly represent central self-medication reasons like reducing inner restlessness, mood fluctuations, or sleeping disorders. The results suggest that the patterns of use motives of patients with ADHD seem to be very similar to those of patients without ADHD, and their treatment should, thus, not only focus on ADHD-specific use motives. It rather is important to consider which use motives are predominant at the time of treatment. Patients at the beginning of their ATS use -possibly with an ATS abuse but not an ATS addiction -may need a treatment primarily based on enhancement motives. In contrast, patients with a longer ATS use history or an ATS addiction presumably need a treatment based on coping and enhancement motives.
Surprisingly, patients with ADHD used ATS less often out of social motives in the latest month of use than patients without ADHD. Well-known daily challenges of patients with ADHD in their social relationships and behavior -like interrupting, talking excessively, noisiness, and difficulty waiting for their turn [42] -lead to frequent rejection by their peer group [43,44]. ADHD seems to be associated with less stable and poorer quality friendships [44], which may explain why social motives are equally important in the first month of ATS use but not in the latest.
All in all, the investigation of both the quantitative and qualitative data offers a quick and economical overview via the AMQ and, where needed, a differentiated study of the ATS use motives via mind maps. We get more precise information about the reasons for ATS use and we can utilize this information for therapeutic treatments. For example, we not only know that a certain patient uses ATS out of coping motives but also we know he or she uses ATS to reduce depressive symptoms. Thereby, therapy can be highly individualized and can be adapted to the needs of every patient against the background of his or her individual explanation model for the disorder(s). Moreover, the mind mapping technique helps patients to reflect on their behavior patterns and supports therapeutic treatments by developing a greater understanding for the functionality of these patterns. Nevertheless, this study also has limitations. The participants were asked to recall their use motives for the first and the last month of ATS use. As in any retrospective survey of drug use, there is a possibility that the results are biased by this recall [45]. However, a prospective approach could not be integrated into our study design. To this end, large-scale longitudinal studies would be needed to address people who might get addicted in the future. Moreover, researches [46,47] confirmed that while the mean levels of use motives may be biased, the principal 4-factor classification of motives is extremely robust over time, age, culture [46], and different domains of human functioning such as gambling [21], sexual risk-taking behavior [22], internet use [20], and listening to music [23]. Considering the difficulty of measuring the use motives directly in the first and latest month of use, retrospective data seem to be a good trade-off between feasibility of data acquisition and accuracy.
The sample size was rather small but can be regarded as sufficient against the background that it is a clinical sample with the usual challenges (e.g., approaching ATS users and convincing therapists of the benefits of participating in the study). We inquired the variable ADHD/ NON ADHD by asking the participants whether they had been diagnosed with ADHD in the past. We refrained from performing a standardized ADHD symptoms screening since existing ATS use-related symptoms may lead to false-positive results. Instead, we collected further information on the ADHD histories to substantiate the self-declarations.
In order to work with the mind mapping technique, participants need to have abstract skills and competencies in reading and writing. For most of the patients, this was not a problem, only a few patients had questions regarding the technique or needed help in writing down their ideas.

Conclusions
The quantitative and qualitative data showed that patients with and without a history of ADHD did not differ in the motive patterns, leading to an incident of ATS use, both in the beginning and the end of the patients' history of ATS use. The only exception was that patients with a history of ADHD mentioned social motives less often in the mind maps for their latest month of use. Similarly, the frequency of individual motives stated in the mind mapping technique showed no indication that "self-medication" played an important role in the ADHD group. Thus, we suggest that an ATS treatment program addressing use motives does not necessarily have to be different for patients with and without a history of ADHD but has to consider the time of treatment (at the beginning of the ATS use or after a longer ATS use history).

Statement of Ethics
The Ethics Council of the University of Bamberg granted permission to conduct the study, and the participants have given their written informed consent.