adverse event; adverse reaction; adverse outcome
Medical term for any untoward medical occurrence in a patient or clinical investigation subject administered a pharmaceutical product, which does not necessarily have a causal relationship with the treatment.
A serious adverse event was reported during the clinical trial.
Known adverse reactions to this drug include headache and nausea.
副作用 refers specifically to side effects with a known causal link to a treatment, while 有害事象 is a broader term that includes any adverse medical occurrence regardless of causality.
Compound of 有害 (harmful) and 事象 (event, phenomenon), likely a calque from English 'adverse event' used in medical contexts.