What Is FAERS? Understanding FDA Adverse Event Data

What Is the FDA Adverse Event Reporting System?

The FDA Adverse Event Reporting System, known as FAERS, is a computerized database maintained by the U.S. Food and Drug Administration. It stores reports of adverse events, medication errors, and product quality complaints for drugs and therapeutic biological products. Since its inception, FAERS has accumulated millions of reports and serves as one of the primary tools the FDA uses for post-market drug safety surveillance.

When the FDA approves a drug, clinical trials have typically involved thousands of patients over a relatively short period. FAERS extends that safety monitoring into the real world, where millions of patients take medications under a much wider variety of conditions, for longer durations, and alongside other drugs that may not have been part of the original trials.

How Reports Enter the System

Adverse event reports come from several sources. Healthcare professionals — including doctors, pharmacists, and nurses — can submit reports when they observe an unexpected or serious reaction in a patient. Consumers and patients themselves can also file reports directly with the FDA through the MedWatch program.

Drug manufacturers have a legal obligation to report adverse events they learn about. This is called mandatory reporting. If a pharmaceutical company receives a report of a serious adverse event from any source, they must forward it to the FDA within 15 days. Less serious events must be reported quarterly.

It is important to understand that voluntary reports from healthcare professionals and consumers represent only a fraction of actual adverse events. Studies suggest that only 1 to 10 percent of adverse events are ever reported to the FDA. This underreporting means that FAERS data should be viewed as a signal detection tool rather than an exact count of problems.

What a FAERS Report Contains

Each FAERS report typically includes the following information:

• Patient demographics — age, sex, and weight (when available)
• Drug information — the suspect drug, concomitant medications, dose, and route of administration
• Adverse event description — the reported reaction using standardized medical terminology (MedDRA)
• Outcome — whether the event resulted in hospitalization, disability, death, or other serious outcomes
• Reporter type — whether the report came from a healthcare professional, consumer, or manufacturer

Not all fields are always filled in. Many reports have missing demographic data, incomplete drug information, or vague descriptions of the adverse event. This incompleteness is one of the known limitations of the database.

How Drug Fact Check Uses FAERS Data

On this site, we pull data from the openFDA API, which provides programmatic access to FAERS records. For each drug, we aggregate the total number of adverse event reports, count serious outcomes including deaths, and list the most commonly reported reactions.

When you visit a drug page, you see a summary of all reports associated with that drug. The reaction counts show how many times each specific adverse event was mentioned in reports involving that drug. Similarly, our reaction pages show which drugs are most commonly associated with a particular adverse event.

What FAERS Data Can Tell You

FAERS is most useful for identifying potential safety signals. If a drug suddenly accumulates an unusually high number of reports for a specific adverse event, the FDA can investigate further. Some important drug safety actions — including label changes, black box warnings, and market withdrawals — have originated from FAERS signal detection.

For individuals, FAERS data can provide a general picture of what kinds of reactions have been reported with a medication. If you are taking a drug and experiencing a particular symptom, seeing that others have reported the same symptom may be useful context to bring to a conversation with your doctor.

What FAERS Data Cannot Tell You

There are several critical limitations to keep in mind:

No proven causation. A FAERS report means someone experienced an adverse event while taking a drug. It does not prove the drug caused the event. The patient may have had an underlying condition, taken other medications, or experienced a coincidental health problem.

No incidence rates. FAERS does not tell you how common a side effect is. To calculate a true incidence rate, you would need to know how many people took the drug without experiencing the event — information FAERS does not contain.

Reporting bias. Drugs that receive media attention, newly approved drugs, and drugs used for serious conditions tend to have more reports. A drug with 50,000 reports is not necessarily more dangerous than one with 500 reports — it may simply be more widely used or more closely monitored.

Duplicate reports. The same adverse event may be reported multiple times by different parties — the patient, their doctor, and the drug manufacturer might all file separate reports for a single incident.

How to Interpret Report Counts Responsibly

When you see that a drug has thousands of adverse event reports on this site, consider the context. A drug taken by 20 million people per year with 10,000 reports has a very different risk profile than a drug taken by 10,000 people with 10,000 reports.

Similarly, the “death reports” count does not mean the drug killed that many people. It means that many reports listed death as the outcome while the patient was taking the drug. The patient may have died from their underlying disease, an accident, or any number of unrelated causes.

Use FAERS data as one piece of a larger puzzle. Combine it with information from your healthcare provider, the drug’s prescribing information, and peer-reviewed research to make informed decisions about your health.

This site is not medical advice. Always consult your doctor or pharmacist before making changes to your medication regimen.