What phase of clinical drug testing assesses long-term effects and adverse reactions after drug approval?

Phase 4 of clinical drug testing, also known as post-marketing surveillance, focuses on monitoring the long-term effects and adverse reactions of a drug after it has been approved for public use. This phase is crucial as some side effects or complications may not emerge during the earlier phases of clinical trials, which typically involve smaller, carefully selected populations and shorter follow-up times.

During Phase 4, the drug is administered to a larger and more diverse patient population in real-world settings, allowing researchers and healthcare professionals to gather comprehensive data regarding its safety and effectiveness over an extended period. This phase can result in the identification of rare side effects, interactions with other medications, or additional indications for the drug's use that may not have been apparent during earlier testing phases. The insights gained during Phase 4 can lead to updated labeling, recommendations for the use of the drug, or even market withdrawal if significant safety concerns arise.