Washout Period: How Long Until a Drug Clears
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[Glossary · How doses act in the body]

Washout period

Also called washout, clearance period, drug-free period · Reviewed

Definition: A washout period is a stretch of time without a drug, long enough for the body to clear most of it before something else starts or a measurement is taken. In FDA study design, an adequate washout is at least five half-lives, or until levels fall to 5% or less of the peak.

Why it matters when you track doses

A washout comes up when switching drugs, before a lab test that should not be skewed, before a planned pregnancy, or in a study comparing two products. It is the reason a drug can still be at work after your last logged dose.

Real label examples: the Ozempic label says semaglutide stays in circulation for about 5 weeks after the last dose. The Ozempic Medication Guide says to stop at least 2 months before a planned pregnancy. The Wegovy label, switching from the 2.4 mg injection to the tablet, starts the tablet one week after the last shot, a switch rather than a full washout.

Worked example: five half-lives

Five half-lives for three drugs

  1. Semaglutide, half-life about 1 week: 5 × 1 = about 5 weeks.
  2. Tirzepatide, half-life about 5 days: 5 × 5 = 25 days.
  3. Testosterone cypionate, half-life about 8 days: 5 × 8 = 40 days.
  4. At that point about 3% of the last dose is left (0.5 to the 5th power = 0.03125).

This uses the simple model where each half-life halves what is left. Real people vary with body size, injection site and kidney or liver function. Five half-lives describes the drug leaving. It says nothing about how fast your own hormones or symptoms return.

Common mix-ups

  • A washout is not a missed dose. It is planned. For an unplanned gap, see the missed dose guides.
  • A label switch plan beats a rule of thumb. When a label gives a specific gap, as Wegovy does, that is the figure for that product.
  • Off-cycle is not automatically washed out. Two weeks off a drug with an 8-day half-life is under two half-lives.

Read more on Dose Track: Half-life calculator · Missed dose guides · Semaglutide vs tirzepatide

General education drawn from labels and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your product are the final word.
Half-lifeHalf-life is the time it takes for the amount of a drug in your body to fall by half. After one half-life,… Cycle (on/off cycling)A cycle is a planned stretch of taking a compound followed by a stretch off it, such as "8 weeks on, 4… Steady stateSteady state is the point, after repeated doses on a fixed schedule, where the amount cleared between… Titration (dose escalation)Titration means adjusting a dose in planned steps, usually starting low and going up, until a target or…

Frequently asked questions

How long is a washout period?+
It depends on the drug. FDA study guidance uses at least five half-lives, or until levels drop to 5% of the peak. For semaglutide that is about 5 weeks.
How long before pregnancy should semaglutide be stopped?+
The Ozempic Medication Guide says at least 2 months before a planned pregnancy. Discuss timing with your prescriber.

Sources

  1. FDA guidance for industry: Bioavailability Studies Submitted in NDAs or INDs, General Considerations (April 2022)
  2. Ozempic (semaglutide) US prescribing information, section 12.3 and Medication Guide, DailyMed
  3. Wegovy (semaglutide) US prescribing information, sections 2 and 12.3, DailyMed
  4. Mounjaro (tirzepatide) US prescribing information, sections 2.1, 7.2 and 12.3, DailyMed
  5. Depo-Testosterone (testosterone cypionate) US prescribing information, DailyMed

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