Understanding the substance use of autistic adolescents and adults: a mixed-methods approach

BACKGROUND: Autistic individuals might be more likely to misuse substances than non-autistic individuals. Better understanding of these patterns can help clinicians identify strategies to reduce substance use, protecting physical and mental health. The aim of this study was to compare the experiences of substance use between autistic and non-autistic adolescents and adults. METHODS: This study is a mixed-methods study, including both quantitative (closed-ended questions) and qualitative (one open-ended question) online assessments. Data were collected as part of a larger study, the Autism and Physical Health Survey, in which we administered an anonymised, online questionnaire to autistic and non-autistic individuals aged 16-90 years. In the present study, we investigated data on substance use or misuse, using two overlapping but separate samples from the survey (one sample with complete quantitative responses and one sample with complete qualitative responses). Binary measures of substance use were investigated using unadjusted and adjusted binomial logistic regression models. Content analysis was used to compare experiences of autistic and non-autistic adolescents and adults. We used Fisher's exact tests to assess differences in frequency of reporting particular qualitative themes and subthemes. FINDINGS: Survey recruitment was done between Feb 7, 2018, and Aug 26, 2019. At the end of the recruitment, 3657 individuals had accessed the survey. After excluding duplicates as well as participants with missing or incomplete responses, we had data from 2386 participants (1183 autistic and 1203 non-autistic participants; 1571 female and 815 male participants) for the quantitative analyses and data from 919 participants (429 autistic and 490 non-autistic participants; 569 female and 350 male participants) in the qualitative analyses. The samples for the quantitative and qualitative analyses were predominantly composed of female individuals, White individuals, UK residents, and those without intellectual disability. Autistic individuals were less likely than non-autistic individuals to report consuming alcohol regularly (16·0% of autistic individuals vs 22·2% of non-autistic individuals; adjusted model: odds ratio OR 0·69, 95% CI 0·55-0·86; p=0·0022) or binge-drinking (3·8% vs 8·2%; adjusted model: OR 0·38, 0·26-0·56; p<0·0001). Autistic male participants were less likely than non-autistic male participants to report ever having smoked (50·8% of autistic male participants vs 64·6% of non-autistic male participants; adjusted OR 0·50; 0·32-0·76; p=0·0022) or ever using drugs (35·4% vs 52·7%; adjusted OR 0·53; 0·35-0·80; p=0·0022). Regarding our qualitative analyses, among participants who reported a specific motivation for drug use, compared with non-autistic individuals, autistic individuals were nearly nine times more likely to report using recreational substances to manage behaviour (OR 8·89, 2·05-81·12; p=0·0017) and more likely to report using recreational substances to manage mental health symptoms (OR 3·08, 1·18-9·08; p=0·032). Autistic individuals were also more likely to report vulnerability associated with substance use (OR 4·16, 1·90-10·05; p=0·00027), including childhood use of drugs and being forced or tricked into using drugs. INTERPRETATION: Autistic individuals might be less likely than non-autistic individuals to report engaging in substance misuse. They also report using drugs to self-medicate. Clinicians should be aware of vulnerability linked to substance use among autistic patients and should work cooperatively with patients to effectively manage autistic and comorbid symptoms. FUNDING: Autism Research Trust, Rosetrees Trust, Cambridge and Peterborough NHS Foundation Trust.