What is the difference between phase 2 and phase 3?

Phase 2 asks whether the drug seems to do anything at all, usually in tens to a few hundred people. Phase 3 asks whether it beats the best treatment already available, usually in several hundred to several thousand.

Phase 3 is usually the one that decides whether a drug gets approved, and usually the one with a comparison group. Ask which phase yours is, because it tells you what is really being asked of you.

Written by two physicians. Checked against patient information from the US National Cancer Institute and Cancer Research UK.