OBJECTIVE : Methodological research has been undertaken to investigate the many challenges in searching for adverse effects data. It is imperative that the search approach adopted in systematic reviews is based on the best available evidence. We provide a detailed summary of the results and implications of the current evidence base to assist future searches for adverse effects. METHODS : This article is a narrative review from the authors of the Cochrane Handbook chapter on adverse effects. RESULTS : The specified search strategy must be based on the population, intervention, comparator, outcome(s) format for question formulation and appropriate study designs for adverse effects data. Search filters and suggested search terms are available for the adverse effects of drug, medical devices, and surgical interventions. The use of generic adverse effects terms (such as harms and complications) as text words and indexing terms and specific adverse effects terms (such as rash and wound infection) are warranted. Searching databases beyond MEDLINE has proven useful, as well as the use of nondatabase sources. CONCLUSIONS : This article provides the most up-to-date evidence-based guidance in identifying adverse effects data in the literature. It will support searchers and researchers evaluating the potential for harm of medical interventions in systematic reviews.