OBJECTIVE: Whether for spiritual, recreational, or potential therapeutic use, interest in ayahuasca has grown remarkably. Ayahuasca's main active substances are N,N-dimethyltryptamine and certain monoamine oxidase inhibitor β-carbolines. Possible drug interactions are a major concern, and research is lacking in this area. The objective of this study was to evaluate the safety of ritual ayahuasca use regarding adverse effects and risk factors. METHODS: In this cross-sectional study, ayahuasca users from a religious institution answered an online questionnaire about its safety. Adverse effects, safety measures, and possible risk factors (psychiatric diagnosis and medications) were investigated. RESULTS: The most frequent adverse effects among the 614 participants were transient gastrointestinal effects (nausea and vomiting). Fifty participants self-reported a psychiatric diagnosis (depression and anxiety were the most prevalent), and these participants experienced adverse effects more frequently. Psychiatric medication use was reported by 31 participants. No indication of increased adverse effects due to drug-drug interactions was found. CONCLUSION: A minority of participants reported being very negatively affected by persistent adverse effects. Psychiatric medication use while participating in ayahuasca rituals was not associated with increased adverse effects. For the most part, the institution's practices seem sufficient to prevent exacerbated reactions. Future studies may focus on negatively affected users.