How does Phase 4 differ from Phase 3 clinical trials?

Phase 4 clinical trials, also known as post-marketing surveillance studies, focus on the long-term effects and health impacts of a drug after it has received regulatory approval. This phase is crucial because it allows researchers and health authorities to monitor the drug's safety in the general population, assessing any adverse effects that may not have been evident in earlier trial phases. Phase 4 trials can also provide insights into the drug's effectiveness in a broader population and may include various populations that were not represented in earlier phases.

Phase 3 trials, on the other hand, primarily evaluate the drug’s efficacy and side effects in a more controlled environment, typically involving a larger and more diverse group of participants than earlier phases. While they do consider side effects, their main aim is to establish the overall benefit-risk profile of the drug before it is approved for market use.

Thus, option C accurately captures the essence of Phase 4 trials, highlighting their role in assessing long-term usage and health outcomes beyond the controlled settings of earlier phases.