adverse event

adverse event (plural adverse events)

2. (medicine, pathology) Any occurrence that has any negative (deleterious) influence (in any degree from mild to severe).

   Hyponyms: adverse effect (loosely synonymous), side effect (loosely synonymous)

   adverse events in the treatment group

   adverse events in the control group

• In precise usage, some writers preserve the distinction that an event that happens during a scientific study either may or may not be an effect (as in cause and effect) of the treatment being tested (correlation does not imply causation); thus they prefer the term adverse event generally and reserve the term adverse effect for known or likely causation. But in imprecise usage the two terms are often used synonymously.