Supplementary Material for: Polydrug use typologies of regular ecstasy users visiting electronic dance music events: A Latent Class Analysis

Background Polydrug use patterns of young adults using ecstasy vary, as well as their willingness to change them. Polydrug use patterns are likely associated with different adverse health outcomes. It is unknown whether polydrug use patterns of young adults that use ecstasy are similar in different countries. Objective This study aims to identify and compare polydrug use patterns and willingness to change it of young adults that use ecstasy in the United Kingdom (UK) and the Netherlands, two countries with a high prevalence of ecstasy use and a large electronic dance music (EDM) scene. Method The data from the online cross-sectional Electronic Music Scene Survey was used in a latent class analysis. The binary indicators used in the estimation were past year substance use of 21 different substances. The sample consisted of young adults ecstasy users that regularly visit EDM events (age 18-34). Results 1077 respondents from the UK (age M=23.1 ) and 1178 from NL (age M=23.7)) that regularly visit EDM events were included in the analyses. In both countries, three polydrug use patterns of ecstasy users were identified based on BIC fit indices: a traditional polydrug use class (UK: 28%; NL: 40%), a stimulant and ketamine polydrug use class (UK: 48%; NL: 52%), and an extensive polydrug use class (UK: 24%; NL: 8%) characterized by substantial use of stimulants, depressant and psychedelic substances. Overall, young adults that used ecstasy in the UK consumed 3,4-Methylenedioxymethamphetamine (MDMA) more often as powder/crystalline and at higher dosages compared to young adults in NL who preferred MDMA tablets. Regardless of polydrug class or country, most respondents indicated that they had the intention reduce but not quit their use. Conclusions In both countries, structurally similar polydrug use patterns among young adults that use ecstasy were found, while the use frequencies of individual substances and preferred MDMA form varied between the countries.