A gap in a programme with no compound taken, long enough for what was already taken to leave the body. In trials a washout separates two treatment periods so the first cannot contaminate the second, and its length is calculated from how fast the compound clears. In community use the word usually just means a break, with no calculation behind it.

Why it matters here

Whether a break is long enough depends entirely on how quickly the particular compound clears, which varies enormously, so a gap that works for one cannot be reused for another. If you are reading a crossover trial, the washout between arms is one of the things that decides whether its result can be trusted at all.

Also called

• washout
• wash out
• wash-out
• washout period
• clearance period
• elimination period
• break
• taking a break
• drug holiday
• flush out
• clearing out

Drug holiday and break are the informal names for the same gap. Washout itself is borrowed from trial design, where it carries a precise meaning tied to how fast the compound is eliminated.

Compounds carrying this term

None on file yet. This term is in the controlled vocabulary but no compound record currently uses it — which is a statement about our coverage, not about the term.

See also

• Cycle — Dosing and scheduling
• On-Cycle and Off-Cycle — Dosing and scheduling
• Half-life — Body and drug basics
• human_rct — Evidence Tier