Adverse Drug Reactions (Adverse Drug Effects) By Daphne E Smith Marsh, PharmD, BC-ADM, CDCES, University of Illinois at Chicago College of Pharmacy Reviewed / Revised Mar 2023 View Patient Education Etiology Symptoms and Signs Diagnosis Treatment Prevention Topic Resources Classification of Adverse... Adverse drug reaction (ADR, or adverse drug effect) is a broad term referring to unwanted, uncomfortable, or dangerous effects that drugs (including medications) may have.