Washout period between clinical trials

Paid Trial Alerts · Phoenix, Arizona · first-hand Phase 1

The gap between studies is the number that decides your year: how many studies you can do, and when the next one can start. Here's who sets it, how it's counted, and why the number you heard from another volunteer may not be your number.

The short answer

A washout period is the required gap between your last dose of an investigational drug in one study and your first dose in the next. It is set by each study's protocol — the sponsor writes it into the eligibility criteria — and screening staff enforce it. It is not a clinic house rule and not a single legal number that applies everywhere.

Who sets the number

The sponsor, per protocol. The window depends on what you took last — how long that compound stays active in your body — and on what the new study is testing. That's why two studies at the same clinic can demand different gaps, and why the screener asks what drug your last study dosed, not just when it ended.

Common patterns — and their limits

• "30 days since last dose" is the floor volunteers see most often in Phase 1 exclusion criteria.
• "Five half-lives of the previous drug, whichever is longer" is the other common form. A half-life is the time it takes the drug's level in your body to drop by half; after about five of them the compound is essentially gone. For a drug that clears slowly, five half-lives can be much longer than a month.
• Long-acting drugs and biologics can carry exclusions measured in months, not days — that's the protocol respecting the drug, not the clinic being difficult.

The only number that binds you is the one in the protocol you're screening for. We don't publish a table of washout rules by clinic because no such table can be true — the rule lives in the study, not the building.

How it's counted

Most protocols count from your last dose, not your discharge date or your follow-up visit — but not all. If you finished a long confinement, those can be weeks apart, and the difference decides whether you're eligible today or next month. Ask the screener which date their protocol uses, and keep your own record of every study: clinic, compound if you know it, and last dose date.

How it's enforced

Three layers: the screener's questions, subject registries at member sites — that's what VCT and CTSdatabase exist for — and your own honesty. Trying to slide under a window is a bad trade everywhere: two investigational drugs in your body at once is a real interaction risk, it corrupts the data both sponsors are paying for, and a caught attempt follows you at that clinic and its network.

The practical playbook

• Keep a study log. Study name, clinic, compound if known, last dose date. Every screening call starts with these.
• Lead with your last-dose date when a recruiter calls — it saves both of you a wasted screening visit.
• Plan around the window. Your washout end date is known the day you dose. Knowing which studies open around that date is the part you can't control — that's the part alerts fix.