During which phase of clinical testing is efficacy first tested for?

Efficacy is first tested during Phase II of clinical studies. This phase follows initial safety assessments performed in Phase I, where the primary focus is on determining a drug's safety profile, dosage range, and pharmacokinetics.

In Phase II, researchers begin to evaluate the therapeutic effectiveness of the drug on a specific condition or disease. This phase typically involves a larger group of participants who have the condition the drug is intended to treat, allowing for a more comprehensive assessment of how well the drug works. The data collected in this phase help determine whether the benefits observed justify proceeding to further testing in Phase III, where efficacy is confirmed in larger populations and against established standards of care.

Phase III focuses on definitively proving efficacy and monitoring adverse effects in a diverse population, while Phase IV occurs after a drug has received approval, focusing on post-marketing surveillance and long-term effectiveness.