Washout period

A short waiting stretch before a trial starts, so an earlier medicine can clear your system first.

A washout period is a planned pause before a trial’s treatment begins, giving an earlier medicine time to leave your body. The idea is simple: if a previous drug is still active in your system, it could blend with the study treatment and make the results — and your safety — harder to read clearly.

How long a washout lasts depends on the medicine and is written into the study’s protocol, so it’s the same for everyone in that trial. You may see it mentioned in a trial’s eligibility criteria. If a washout would mean stepping away from a treatment that’s helping you, that’s an important thing to talk through with your care team first.