Nowadays, adults with autism spectrum disorder (ASD) experience several comorbidities whose treatment implies a wide range of psychotropic prescriptions. This study aimed to evaluate medication-related safety, drug-drug interactions, and psychotropics prescription trends. We conducted an observational and multicentric pharmacovigilance study in subjects with ASD and Intellectual disability (ID, n = 83). Clinical information (diagnoses, ongoing medications, comorbidities [multimorbidity ≥ 4 chronic health conditions]) and psychotropic prescriptions (polypharmacy ≥ 4 chronic drugs, daily drug doses, co-prescription) were registered. Ethical approval for this study was obtained. Participants (30±10 years old, 86% men, BMI 27±6 kg/m2) displayed 37% multimorbidity (mean of 3, IQR 2-4), and 57% polypharmacy (13% out of dose recommended range). Most drugs prescribed were psychotropic risperidone which is related to nervous system comorbidities (18% epilepsy, 16% insomnia, and 14% psychotic agitations). Risperidone and quetiapine were co-prescribed in 60% of the cases without any monitoring adverse event routine. The rates of multimorbidity and polypharmacy, among our young adults with ASD and ID, are concerning. Data suggest the need to develop a pharmacovigilance monitoring system to evaluate prescription accuracy, long-term safety of ongoing medications, and the fixed doses in this autistic population with associated ID.Copyright © 2020 Elsevier B.V. All rights reserved.