Which phase of clinical trials typically involves testing on a large group of patients to assess efficacy and monitor adverse reactions?

The phase of clinical trials that typically involves testing on a large group of patients to assess efficacy and monitor adverse reactions is Phase III. This phase is crucial as it serves to confirm the effectiveness of the treatment in a larger, diverse population and to further evaluate its safety. During Phase III trials, thousands of participants are often involved, allowing researchers to gather comprehensive data on how the drug performs across different demographics and conditions.

In addition to measuring efficacy, Phase III trials closely monitor for any adverse reactions or side effects, helping to ensure that the benefits of the treatment outweigh any risks. The successful completion of Phase III is often a requirement for regulatory approval, making it a pivotal step in the drug development process.

Phase I trials usually involve a small group of healthy volunteers and focus primarily on safety and dosage. Phase II trials involve a larger patient group but are still relatively small compared to Phase III and are primarily designed to assess the drug's efficacy and further evaluate safety. Phase IV occurs after a drug has been approved and marketed, focusing on the long-term effects and broader population use.