What phase of clinical trials focuses on long-term effects of a drug?

The focus on long-term effects of a drug is primarily associated with Phase IV clinical trials. These trials occur after a drug has received approval from the regulatory authorities and is on the market. The purpose of Phase IV is to monitor the drug's long-term safety, effectiveness, and any unexpected adverse reactions in a larger and more diverse population over an extended period. This phase helps to determine the long-term impacts and benefits of a medication, which can include assessing how it performs in the general population outside of the controlled conditions of earlier trial phases.

In contrast, early trial phases concentrate on different objectives; for example, Phase I focuses on safety, dosage, and pharmacokinetics in a small group, Phase II assesses efficacy and side effects in a somewhat larger population, and Phase III involves large groups to compare the new drug to standard treatments for effectiveness and to gather more comprehensive safety data before market approval. Each of these earlier phases is critical for drug development, but they do not address long-term outcomes as extensively as Phase IV.