Any unwanted medical occurrence during a study—whether or not it was actually caused by the treatment.An adverse event (AE) is any unfavorable medical occurrence in a patient administered a pharmaceutical product, regardless of causal relationship. Adverse events are graded by severity (mild, moderate, severe) and classified by seriousness (serious adverse events require hospitalization, are life-threatening, or cause death). The distinction between AE and adverse drug reaction (ADR) is causality: all ADRs are AEs, but not all AEs are drug-related. Clinical trial safety data reports AE incidence in both treatment and placebo groups to establish attribution.