Which phase of clinical trials focuses on post-marketing surveillance?

The phase of clinical trials that focuses on post-marketing surveillance is Phase IV. This phase occurs after a drug has received approval from regulatory authorities and has been made available to the public. The main goal of Phase IV trials is to monitor the drug's long-term effectiveness, safety, and impact on the population. It helps identify any rare or long-term side effects that were not apparent during the earlier phases of clinical trials, where the sample sizes are typically smaller and the duration shorter.

In Phase IV, the drug is used in a larger, more diverse population, which can offer insight into how it performs in real-world conditions compared to the controlled settings of Phases I through III. This ongoing assessment helps ensure that the benefits of the drug continue to outweigh any risks once it is widely prescribed to patients in the general population.