Efficacy is the ability of a clinical trial drug or treatment to create the desired therapeutic effect. Efficacy is studied in Phase II of a clinical trial, and confirmed in Phase III.

We evaluate efficacy under highly controlled conditions, and thus the performance of the intervention may not be completely replicated in a real-world setting.

Source: NIA Glossary of Clinical Research Terms. (n.d.). National Institute on Aging. Retrieved January 8, 2022, from https://www.nia.nih.gov/research/dgcg/nia-glossary-clinical-research-terms