Serious adverse event (SAE)

A serious adverse event is any unwanted medical occurrence during exposure to a substance that results in death, is life-threatening, requires hospitalization, causes lasting disability, or produces a birth defect.

The definition comes from regulatory guidance and is applied in every clinical trial regardless of whether the event is thought to be caused by the study substance. Serious is a regulatory category based on outcome, distinct from severe, which describes intensity; a severe headache is not a serious adverse event, while a mild reaction that leads to a hospital stay is. Investigators must report serious adverse events to regulators and ethics committees within set timeframes.

Serious adverse events are a primary safety endpoint in cannabinoid trials. In studies of prescription cannabidiol, events classified as serious included elevated liver enzymes leading to discontinuation and, in a small number of cases, hospitalization for other reasons. Reading a trial's serious adverse event count alongside its total adverse event count gives a fuller picture of tolerability. Consumers and clinicians can report serious events involving retail CBD products to the U.S. Food and Drug Administration.