Adverse event
AEAn adverse event is any unwanted medical occurrence in a person or animal during exposure to a substance, whether or not the substance caused it.
The definition is deliberately broad. It covers anything from mild drowsiness to a hospital admission, and it does not require proof of cause; a headache during a clinical trial counts even if it turns out to be unrelated. Investigators record every event, then assess how likely it is that the study substance was responsible. Events are graded by severity, and those meeting certain thresholds are classified separately as serious adverse events.
In clinical trials of prescription cannabidiol, the most commonly reported adverse events included somnolence, decreased appetite, diarrhea, and elevated liver enzymes, generally at doses well above those found in retail products. Consumers can report suspected adverse events involving CBD products to the U.S. Food and Drug Administration through its MedWatch program. Reading an adverse event list on a product insert or study report is a way to understand tolerability, not a prediction that any single person will experience those effects.