Adverse event (AE)
In Safety & pharmacovigilance
An adverse event is any unfavorable medical occurrence in a participant during a trial, whether or not it is thought to be caused by the study treatment. It can be a new symptom, an abnormal test result judged clinically significant, or the worsening of an existing condition. The key point is that no causal link is implied by the term itself.
| Term | What it means |
|---|---|
| Adverse event (AE) | Any unfavorable medical occurrence in a participant. The term does not imply that the treatment caused it. |
| Adverse drug reaction (ADR) | An adverse event where a causal link to the investigational product is at least a reasonable possibility. |
| Serious adverse event (SAE) | An adverse event that results in death, is life-threatening, requires or prolongs hospitalization, causes persistent or significant disability or incapacity, or is a congenital anomaly or birth defect. |
Where the rule comes from
ICH E6(R3) defines an adverse event in its Glossary as any unfavorable medical occurrence in a trial participant administered the investigational product, with no causal relationship implied. Annex 1, section 2.7.2 sets the investigator's duties: report adverse events to the sponsor as the protocol specifies, report serious adverse events to the sponsor immediately after becoming aware of them with an assessment of causality, and report events before the first dose (for example during screening) if the protocol requires it.
Why it matters
Recognizing that an adverse event does not mean the drug caused it is the single most common misunderstanding among people new to clinical research, and it comes up in interviews.
Example
A participant twists an ankle playing football during the study. It is an adverse event even though nobody thinks the study drug caused it.
Common questions
- What is the difference between an adverse event and an adverse reaction?
- An adverse event is any unwanted medical occurrence, related or not. An adverse reaction is an adverse event for which there is at least a reasonable possibility that the study treatment caused it.
Related terms
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