2.2. Substance use and clinical assessment

To objectively assess substance‐use over the past 4 months, a toxicological hair analysis with liquid chromatography–tandem mass spectrometry (Scholz et al., 2021) was carried out by the Institute of Forensic Pharmacology and Toxicology, Zurich. This allowed the validation of MDMA‐intake within the past 4 months in the MDMA‐user group. Subjective history of current and lifetime substance consumption was inquired with a structured and standardized Interview for Psychotropic Drug Consumption (Quednow et al., 2004). Amounts and frequency of present and past consumption of all known psychotropic substances were quantified on this basis.

The Mini‐International Neuropsychiatric Interview (Sheehan et al., 1998) was used to screen for psychiatric disorders. Substance use disorders were assessed by the Structured Clinical Interview for DSM‐5 Axis I diagnoses, Module E (First, 2014). For additional assessments of depressive symptoms and sleep disturbances the Center for Epidemiologic Studies Depression Scale (Eaton et al., 2004) was applied. Symptoms of attention deficit/hyperactivity disorder (ADHD) were assessed with the ADHD Self‐Rating Scale (Rösler et al., 2004). Verbal IQ was estimated by a German vocabulary test (Mehrfachwahl‐Wortschatz‐Intelligenztest) (Lehrl et al., 1995).

Self‐reported MDMA amounts assessed with the Psychotropic Drug Consumption Interview were summarized to four representative scores. Those included (1) consumption within the past 12 months, (2) lifetime consumption, (3) maximal intake within a week, and (4) days since the last consumption. Specifically, all scores were z‐transformed first, and next, the summarized scores were calculated as follows: (1) MDMA consumption within the past 12 months = (MDMA occasions within the last 12 months + gram per occasion)/2, (2) lifetime consumption = (years of use + lifetime gram + lifetime occasions)/3, (3) maximal intake within a short timeframe = (max gram per week + max occasions per week + max gram per day)/3, and (4) days since the last consumption constituted another score. To control for substance co‐consumption, a further covariate was calculated (after z‐transforming the respective variables) as follows: (∑(lifetime amounts + gram per occasion intaken within the last 12 months) for cannabis, amphetamine, and cocaine)/6 + (∑(lifetime occasions + occasions within the last 12 months) for cannabis, amphetamine, and cocaine)/6.