Clinical Trial Phase 4

Clinical trials advance to phase 4 after the new treatment being tested has been approved for use. For this reason, a phase 4 trial is sometimes referred to as a post-marketing surveillance trial.

Like phase 3, the phase 4 trial is a large-scale study that may require up to a few thousand volunteers and last for a year or more. The company actively selling the product usually covers the cost of this phase.

Primary Purposes of a Phase 4 Trial

During a clinical trial in phase 4, researchers gather data on the long-term effects of the treatment or device. Does its effectiveness change over time? Do any side effects or health complications appear after participants have used the new medical product for long periods of time?

Another purpose of a phase 4 trial is to compare the new treatment or device to methods previously used to treat the same condition. Both medical practitioners and consumers alike are interested in how one treatment compares to another.

Like every other clinical trial phase, phase 4 is also used for continued safety testing. No medical intervention is without risk, but the more data researchers have about the drug or device, the better they can develop guidelines on its safe use.

Review of a Phase 4 Trial

A phase 4 trial differs from the earlier clinical trial phases in that the treatment in question has already been approved for use in the medical field. However, regulatory agencies—such as the U.S. Food and Drug Administration—still review data from this clinical trial phase. If the results show that the treatment is too risky or it isn’t working as well as it did in earlier phases, the approval of the treatment may be revoked.

In addition to completely withdrawing its approval, the regulatory agency may also amend its approval of the treatment. For example, the agency may decide that the labeling of a new drug should be changed to warn patients of potential risks not previously identified in earlier phases of the clinical trial.


CenterWatch. (2010). Overview of clinical trials. Retrieved December 4, 2010, from

ClinicalTrials. (2007). Understanding clinical trials. Retrieved November 30, 2010, from

National Cancer Institute. (2010). Cancer clinical trials. Retrieved December 4, 2010, from

National Cancer Institute. (2007). New approaches to cancer drug development: Questions and answers. Retrieved December 4, 2010, from