Adverse event

Any noxious, pathological or unintended change in a physical or metabolic function, revealed by signs or symptoms or a change in the results of laboratory tests, in any phase of a clinical study, whether or not the change is considered treatment-related.

Note: It may involve the exacerbation of a pre-existing condition, intercurrent diseases, an accident, a drug interaction or a significant worsening of the disease.

Reference

http://htaglossary.net/adverse-event