A surrogate endpoint is a substitute for a clinical endpoint used in trials where the use of a clinical endpoint might not be possible or practical.
For example, surrogate endpoints are used when the clinical endpoint, like strokes, might take a very long time to study, or in cases where the clinical benefit of improving the surrogate endpoint, such as controlling blood pressure, is well understood. They are also used in cases where conducting a clinical endpoint study would be unethical.
Glossary
Surrogate endpoint