Pharmacovigilance for Health Management: A National Profile of Methylphenidate Adverse Events in Thailand Using National Databases

Background: Methylphenidate, a Schedule II psychostimulant, is indicated for ADHD in children ≥6 years when other measures fail, with unclear adult indications beyond narcolepsy. Global use increases necessitate robust pharmacovigilance, especially in low/middle-income countries like Thailand where safety data is sparse. This study characterized methylphenidate-associated adverse events (AEs) in Thailand, analyzing product types and patient factors. Methods: Spontaneous Thai Vigibase™ reports (2005-2024) were analyzed alongside national distribution data. AEs were MedDRA-coded and stratified by age, sex, indication, formulation (original/generic; immediate/extended-release), allergy history, and comorbidities. Reporting Odds Ratios (RORs) identified safety signals. Serious AEs followed WHO criteria. Results: Among 424 patients (mean age 12±9.06 years; 79% male), 959 AEs occurred. Most frequent were decreased appetite (36%), weight loss (14%), and insomnia (12%). Serious AEs (0.94%) included Stevens-Johnson syndrome, seizures, and angioedema. A novel signal for apathy was detected (ROR 532.45, 95% CI 86.01–2496.41), absent from Thai labeling. Generic formulations had a higher proportion of serious AEs than originators (4.55% vs. 0.85%). Off-label prescribing occurred in 3% of children under six. Conclusions: A significant reporting decline post-2010 indicates substantial under-reporting. Findings underscore the urgent need to strengthen Thailand's pharmacovigilance system through enhanced reporting, regional collaboration, consumer involvement, clearer off-label guidance, and continuous quality assurance to ensure safe psychostimulant use. Keywords: Methylphenidate, adverse drug reactions, pharmacovigilance, rational use, health management and policy