WHAT IS Phase 4

Phase 4 refers to the final of four stages of new drug testing. This phase takes place after the drug has been introduced to the marketplace. Phase 4 testing and reporting builds upon the clinical testing done prior to the drug’s release, but it provides more robust data due to a larger sample size.


Phase 4 research, sometimes referred to as post-marketing surveillance (PMS), takes advantage of larger data sets, more naturalized settings and observational rather than interventional methodologies to provide a real-world complement to the research conducted in the three earlier stages of the testing process. Phase 1 focuses on establishing the safety of a drug for human consumption. Phase 2 examines the efficacy of the drug. Large-scale clinical trials take place in Phase 3, which can take years to compile the data necessary for regulatory approval. Phase 4 expands on that clinical testing to examine the effects, adverse and beneficial, of a drug over an extended period of time and among a larger sample of patients.

Required Reporting and Testing in Phase 4

Once a drug has been approved and marketed to the general public, the U.S. Food and Drug Administration (FDA) requires that firms track and report on adverse side effects of the drug. The FDA’s Adverse Event Reporting System (FAERS) is an electronic database designed to protect public health by compiling comprehensive data on unwanted effects of new drugs. The MedWatch program provides a framework for health professionals to report serious problems with a new drug to the FAERS as well as a gateway to FAERS data for public consumption. Drug manufacturers are required to report adverse effects of a new drug via individual case study reports (ICSRs) as well as accident and drug quality reports when problems arise. Staffers from the FDA’s Center for Drug Evaluation and Research (CDER) routinely review submitted data and assign further research or product modifications when appropriate.

In addition to reporting of problems arising from the marketplace, researchers continue to conduct clinical testing during Phase 4. This testing tends to involves patients who have been taking the drug for an extended time since this extended exposure to the drug provides data that pre-marketing studies are unable to collect. Phase 4 testing is also conducted on a much larger patient base than earlier rounds of clinical trials. Larger patient samples allow researchers to more effectively target specific demographics such as diabetics or pregnant women. While this testing is mandated by the FDA, it is beneficial to the drug manufacturer to the extent that it can identify new markets and applications for a recently approved medication.