Why do regulators monitor harmful reactions after a drug reaches the market?

Regulators monitor drugs after they reach the market because clinical trials, which typically involve several thousand participants, may fail to identify rare or unforeseen adverse events that only appear when a drug is used by a much larger, diverse population.1

For instance, an adverse event occurring in only one out of every 10,000 patients is unlikely to be detected during pre-market testing. Consequently, the FDA and pharmaceutical companies collect and evaluate postmarketing data to identify these risks. This ongoing surveillance is essential because:1

• Safety Assurance: While the risk-to-benefit ratio is favorable for most approved drugs, some products may cause harm through unrecognized severe reactions or toxic impurities.2
• Complexity of Causation: Distinguishing between drug-induced side effects and naturally occurring health issues—such as fever or hepatitis—is often difficult and requires long-term data collection.1
• Public Protection: Effective regulation is a moral imperative to protect the general public from harm, ensuring that any serious risks are identified and communicated as accurately as possible.2