During which phase of clinical trials is a drug's effectiveness typically first evaluated?

In clinical trials, Phase II is where a drug's effectiveness is typically first evaluated. This phase follows Phase I, which primarily focuses on establishing safety, determining dosage, and observing side effects in a small group of participants. During Phase II, the focus shifts to assessing how well the drug works in a larger group of individuals who have the condition that the drug aims to treat.

In this phase, researchers measure the drug's efficacy as well as continue to monitor its safety in a controlled setting. This is vital because it provides preliminary data on whether the drug has the anticipated therapeutic effect and how it performs compared to a placebo or standard treatment, if applicable. The findings from Phase II play a significant role in deciding whether the drug should move on to Phase III, where further evaluations of effectiveness compare it more rigorously against other treatments.

Thus, the evaluation of effectiveness starts in Phase II, making it a crucial step in the drug development process.