Efficacy
Definition
A drug's ability to produce the intended effect under controlled conditions, measured by endpoints set in advance in clinical trials.
Efficacy
Efficacy is how well a drug or treatment produces a benefit under ideal or controlled conditions, such as those in a clinical trial. It differs from effectiveness, which is how well a treatment works in everyday practice, where adherence, other illnesses and other factors complicate things. Regulators mainly look at efficacy data from controlled trials when deciding whether to approve a drug.
Efficacy is measured through endpoints set in advance. In metabolic medicine, common measures include percentage weight loss, change in HbA1c (a marker of long-term blood sugar control) and the share of patients who reach set treatment targets. Whether a result matters clinically depends on two things: its statistical significance (how unlikely it is to be due to chance) and its clinical meaningfulness (whether the effect is big enough to help patients).
In the Phase 2 retatrutide obesity trial, the highest-dose group lost an average of 24.2% of body weight from baseline at 48 weeks, and 100% of participants in that group lost at least 5%. These results beat those reported for other incretin-based drugs and were a major reason retatrutide moved into Phase 3.