Phases of a Clinical Trial


There are four phases of clinical trials.

Phase 1 – Is the Treatment Safe?

Phase 1 clinical trials are the first time an experimental therapy is given to humans.  These trials focus on ensuring that the therapy is safe to use in people, rather than how effective it may be as a treatment for a specific disease. This clinical trial is usually performed in a small group of healthy volunteers who are closely monitored.  In situations where there is a severe or life-threatening illness, volunteers with the disease may participate. During Phase 1 studies, increasing doses of the experimental drug are given so researchers can measure the body’s response, specifically how the drug is absorbed, how long it remains in the blood stream, and which dosage levels are safe and well tolerated.

Phase 2: Does the Treatment Work?

Phase 2 clinical trials assess the effectiveness of the experimental therapy at treating a specific illness or medical condition.  Information about the therapy’s safety, side effects and potential risks are also collected.  It is in this phase that researchers focus on determining the most effective dosages and the most appropriate method of delivery (e.g., tablets, extended release capsules, infusions, injections).  Phase 2 clinical trials involve a larger number of participants who usually have the medical condition that the experimental drug is intended to treat. Patients are monitored carefully and assessed continuously.  Phase 2 trials are discontinued if the drug does not show effectiveness or have safety problems or intolerable side effects.

Phase 3: Is the Treatment Better Than What’s Already Available?

Phase 3 clinical trials test the results of the earlier trials in much larger groups of people and gather additional information on the efficacy and safety of the experimental drug.  This is the final step before seeking approval from the U.S. Food and Drug Administration (FDA). This phase often involves several hundred or thousand participants in many study locations.  These trials are often randomized, which means participants are randomly selected to receive the experimental therapy, placebo, or another therapy, which is also known as a “comparator” drug.  The studies are “double blinded” which means that neither the clinical investigator nor the participant knows whether the therapy given is the true experimental therapy, a placebo (a medication with no active ingredients), or another therapy (“comparator”). Phase 3 trials generally provide information to assess the benefits and risks of the new therapy.  Much of the information obtained and analyzed during the Phase 3 trial is included in the final product label if/when the experimental drug is approved by the FDA.

Phase 4: What Else Do We Need to Know?

Phase 4 trials are also known as “post-approval” or “post-marketing” studies.  These trials are conducted after the drug has been approved and is available to the public. These Phase 4 trials allow researchers to collect additional information about the longer-term risks, benefits and optimal use of the drug. This information is important since even the most well-designed Phase 3 studies might not uncover a problem that could become apparent once the therapy is widely used.