Which phase of a clinical trial is primarily used to assess the efficacy of a drug?

Phase II of a clinical trial is primarily focused on assessing the efficacy of a drug. This stage follows Phase I, where the primary objective is to evaluate the safety and tolerability of the drug in a small group of participants.

During Phase II, the drug is administered to a larger group of people who have the condition the drug aims to treat. This phase is critical for determining whether the drug effectively produces the desired therapeutic effect, while continuing to monitor its safety. Researchers often explore different dosages during this phase to identify the optimal dose that maximizes efficacy with minimal adverse effects. The data collected in Phase II are used to inform the design of Phase III trials, which involve even larger populations and are necessary for confirming efficacy and further assessing risk-benefit profiles before seeking regulatory approval.

Each subsequent phase of clinical trials builds on the findings of the previous ones, with Phase III focusing on confirming the effectiveness in a larger and more diverse patient population and Phase IV, often called post-marketing surveillance, assessing long-term effects after the drug is on the market.