Endpoint
Definition
A measurable trial outcome used to judge whether a treatment works. The primary endpoint is the main result; secondary endpoints add supporting evidence.
Endpoint
In clinical research, an endpoint is a measurable outcome, set in advance, that shows whether an investigational treatment has a meaningful effect. Endpoints are written into the trial protocol before the study starts and form the basis of the statistical analysis. The choice of endpoints shapes the trial’s design, its size and the conclusions it can support.
Endpoints are either primary or secondary. The primary endpoint is the single most important outcome, the one the trial is statistically powered to detect. It drives the sample size calculation and is what regulators base their decisions on. In obesity trials, the primary endpoint is usually the percentage change in body weight from baseline, or the share of participants reaching a clinically meaningful weight loss threshold (such as 5% or 10%). In diabetes trials, it is usually the change in HbA1c from baseline. Secondary endpoints add information on other benefits or risks, such as changes in waist size, blood pressure, lipids or liver fat.
In the Phase 2 retatrutide obesity trial (NCT04881760), the primary endpoint was percentage change in body weight at 24 weeks, with a key secondary endpoint extending this to 48 weeks. The trial also measured many other secondary endpoints, including the share of participants reaching various weight loss thresholds and changes in cardiometabolic risk factors.