Clinical trials, even large ones, can only catch so much. A drug tested in a few thousand or even ten thousand trial participants before approval can still have rare side effects that only become visible once millions of people are taking it. The tool the FDA uses to catch those signals after approval is called FAERS, the FDA Adverse Event Reporting System, and it's the database behind most of the post-approval safety stories that get written about drugs like semaglutide and tirzepatide.
What FAERS Actually Is
FAERS is a database that collects reports of adverse events and medication errors submitted by healthcare professionals, patients, and pharmaceutical companies themselves. Drug manufacturers are legally required to submit reports of adverse events they become aware of; healthcare providers and patients can submit reports voluntarily through the FDA's MedWatch program. Every report becomes part of a public, searchable database that anyone, including researchers, journalists, and this site, can query.
How a Report Gets Filed
A typical pathway looks like this: a patient experiences a symptom or event they believe might be connected to a medication, and either they or their doctor submits a MedWatch report describing what happened, what drug or drugs were involved, and relevant details like dose and timing. Pharmaceutical companies also monitor their own products and are required to submit reports of adverse events reported to them directly, including ones flagged through customer service lines, clinical follow-up, or published case reports.
What FAERS Can Tell You, and What It Can't
This is the most important thing to understand about the database: a report in FAERS is not confirmation that a drug caused the reported event. Anyone can submit a report, the FDA does not verify the accuracy of submissions before they're added to the database, and there's no control group, meaning there's no way to know from FAERS data alone whether an event happens more often in people taking the drug than it would anyway in the general population. What FAERS is genuinely good at is generating a signal, a pattern of similar reports that prompts the FDA to look closer, potentially requesting more data from the manufacturer, commissioning a formal epidemiological study, or in some cases updating a drug's label.
How FAERS Signals Become Real Regulatory Action
A rise in reports alone rarely results in an immediate label change. The FDA typically uses a FAERS signal as the starting point for a more rigorous investigation, which might include reviewing detailed case reports, requesting data from ongoing clinical trials, commissioning analyses of large insurance claims or electronic health record databases (a different, more rigorous form of real-world evidence than FAERS reports themselves), or in some cases requiring the manufacturer to conduct a formal post-marketing study. Only after that more rigorous review does a label change, new warning, or in rare cases a market withdrawal typically follow.
Why This Matters for Peptide Drugs Specifically
GLP-1 drugs are widely prescribed and have been the subject of numerous FAERS-based safety stories in the press, covering everything from gastrointestinal side effects to rarer signals like gallbladder disease and the NAION eye-safety question discussed elsewhere on this site. Because these drugs are taken by a very large population, FAERS naturally accumulates a large raw number of reports for them, which is a function of exposure volume as much as anything else and is exactly why the FDA's more rigorous follow-up investigations, rather than the raw report count, are what actually determine whether a safety concern is real.
The Bottom Line
FAERS is a genuinely useful early-warning system, and its openness to the public is a real transparency strength of the U.S. drug safety system. But a spike in reports about a drug is the beginning of a safety investigation, not the conclusion of one, and readers encountering a FAERS-based headline should treat it as "worth watching" rather than "proven," pending the FDA's more rigorous follow-up analysis. Anyone with a specific concern about a medication they're taking should raise it with their prescribing physician rather than trying to interpret raw adverse-event counts themselves.