Clinical Trial Phases

Phase I clinical trials evaluate the potential safety profile and possible or likely side effects of an investigational drug, in most cases in a small group of healthy people.

Phase II clinical trials further identify side effects and risks associated with the investigational drug and help to determine which dose of the drug works best. Phase II clinical trials are usually conducted with a larger group of people than Phase I clinical trials.

Phase III clinical trials further evaluate an investigational drug’s safety, effectiveness, and side effects in an even larger group of people who have been diagnosed with the medical condition for which the drug is being studied. Phase III clinical trials help to confirm the findings of earlier research and may compare the investigational drug to existing approved treatments or to no treatment, possibly using a placebo. A placebo looks like the investigational drug but does not have the active ingredient. If the investigational drug proves to be safe and effective during phase III trials, it is submitted to the FDA/EMA for approval.

Phase IV clinical trials refers to ongoing testing of a drug that occurs after that drug has been approved and made available to the public, most often to evaluate its long-term effectiveness.