Post-marketing surveillance is a critical component of pharmaceutical regulation, often uncovering unanticipated adverse drug reactions (ADRs) once a drug is widely used over an extended period.

This process, termed pharmacovigilance, aims to detect, evaluate, and minimize harmful effects related to medication use. The data collection for pharmacovigilance depends on spontaneous reporting systems, where healthcare professionals or patients voluntarily report suspected ADRs.

In some cases, there might be a legal obligation to report potential adverse effects. These reported data are then examined for 'signals,' which are potential causal links between the drug and the reported adverse event that were not identified earlier. For validation of these signals, a causality assessment is performed. It involves examining various elements, such as the temporal relationship between drug administration and the ADR, the pharmacological plausibility of the reaction, and the outcomes of dechallenge and rechallenge tests.

Post-evaluation, the causality is classified as definite, probable, possible, or unlikely. Regulatory bodies flag drugs exhibiting adverse effects. These findings are disseminated through channels like drug alerts, medical journals, and updates to drug labels with suitable warnings or precautions. In severe cases, the drug may be removed from the market.