Efficacy
Definition
The ability of a drug to produce the desired therapeutic effect under controlled conditions, as measured by predefined endpoints in clinical trials.
Efficacy
Efficacy refers to the capacity of a drug or intervention to produce a beneficial therapeutic effect under ideal or controlled conditions, such as those maintained in a clinical trial. It is distinct from effectiveness, which describes how well a treatment works in real-world clinical practice, where patient adherence, comorbidities, and other variables introduce additional complexity. Regulatory agencies primarily evaluate efficacy data from controlled trials when making approval decisions.
Efficacy is measured through predefined endpoints. In metabolic medicine, common efficacy measures include the percentage reduction in body weight, the change in HbA1c (a marker of long-term blood sugar control), and the proportion of patients who achieve specific treatment targets. The clinical significance of an efficacy finding depends on both its statistical significance (the probability that the result is not due to chance) and its clinical meaningfulness (whether the magnitude of effect is large enough to benefit patients).
In the Phase 2 retatrutide obesity trial, the highest-dose group achieved a mean weight loss of 24.2% from baseline at 48 weeks, with 100% of participants in that group losing at least 5% of their body weight. These efficacy results exceeded those reported for other incretin-based therapies and were a major factor in the decision to advance retatrutide into Phase 3 development.