Are drugs monitored after FDA approval?

Even after approval, the studies and observation continue. A much bigger group of patients may begin to use a medicine upon approval compared with the thousands of patients in clinical trials and in this larger scale rare side effects may occur, so companies must continue to monitor the drug carefully. The FDA requires them to continue to submit periodic reports, including any cases of adverse events (side effects or complications).
Sometimes, the FDA requires a company to conduct additional studies. Known as Phase IV or "post-marketing" studies, they evaluate long-term safety or generate more data about how the medicine affects a particular group of patients (e.g., children or the elderly).
Phase IV studies can continue for years; one study can cost between $20-30 million. Depending on the findings, a company can use the studies to submit a Supplemental NDA, seeking additional indications for the medicine.