Phase 1 Trial
Definition
The first stage of testing a new drug in people. It checks safety, tolerability and pharmacokinetics, usually in a small number of healthy volunteers or patients.
Phase 1 Trial
A Phase 1 trial is the first stage of testing a new drug in people. Its main aim is to check safety, tolerability and pharmacokinetics, not whether the drug works. Phase 1 studies usually enroll a small number of people, often between 20 and 100. They may be healthy volunteers or patients with the target condition, depending on the drug’s risks and how it works.
Phase 1 trials often use single ascending dose (SAD) and multiple ascending dose (MAD) designs. In SAD studies, small groups each get one dose, starting very low based on laboratory data, and each new group gets a higher dose. MAD studies step up the dose the same way but give repeated doses, to see how the drug builds up and what steady-state levels look like. These designs let researchers find the maximum tolerated dose and the side effects that limit dosing.
For retatrutide, the Phase 1 first-in-human study established its safety at the first dose levels, measured its pharmacokinetics (including the roughly six-day half-life) and gave early signs of activity, including lower glucose and weight loss. These data guided dose selection for the Phase 2 studies that followed.