Evidence-appraisal glossary
Intercurrent Event
Something that happens after treatment starts and changes how a patient's outcome should be read, such as stopping the assigned drug, switching treatments, or taking rescue medication. How these events are handled is central to defining a trial's estimand.
Also called: post-randomization event.
Intercurrent events are not the same as missing data: the outcome may still be observed, but its meaning is complicated by what happened along the way. Trialists choose a strategy for each type, for example ignoring it and counting the outcome anyway (treatment policy), or asking what would have happened without it (hypothetical). The choice can move the estimated effect substantially, so it belongs in the protocol rather than being decided after seeing the data.
Read the full Reading the Evidence blog.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.