RESUMO
INTRODUCTION: Mental illness is a leading cause of non-fatal disease burden worldwide. Natural health products (NHPs) are sought by patients with mental health conditions as a safer and more 'natural' option than conventional pharmacotherapy; however, the possible adverse events (AE) and interactions between NHPs and prescription medicines are not fully known. OBJECTIVES: The aim of this study was to determine (i) the prevalence of adult patients with mental health conditions taking prescription medications only, NHPs only, NHPs and prescription medications concurrently, or neither, (ii) which prescription medications and NHPs are most commonly used, (iii) AEs (serious and non-serious) experienced in the last 30 days for each product use group. METHODS: Mental health clinics in Alberta and Ontario, Canada, were included in an active surveillance study investigating NHP-drug interactions. On their first clinic visit, adult mental health patients were provided with a form inquiring about prescription drug use, NHP use, and any undesirable health events experienced in the last month. Healthcare professionals were also asked to report AEs. RESULTS: A total of 3079 patients were screened at 11 mental health clinics in Alberta and Ontario. In total, 620 AEs were reported in 447 patients (14.9%). The majority of adverse events were seen in patients using both NHPs and prescription medicines (58.8%), followed by patients taking only prescription medicines (37.1%), NHPs only (3.4%) and neither (0.67%). Combining NHPs and prescription medications increases the likelihood of experiencing AEs (OR 2.1; p < 0.001; 95% CI 1.7-2.6). CONCLUSIONS: Adult patients with mental health conditions who are taking both prescription medications and NHPs are more likely to report an adverse event than patients taking prescription drugs or NHPs alone. Polypharmacy increases the likelihood of an adverse event. Active surveillance is feasible and could contribute to enhanced pharmacovigilance.