How Long Do Clinical Trial Phases Take?

Before a potential new treatment can reach patients, it goes through several clinical trial phases that test the treatment for both safety and effectiveness. Together, clinical trial phases take six to seven years on average. Each individual phase takes a different amount of time, with Phase 3 trials lasting the longest.

Before a potential treatment reaches the clinical trial stage, first scientists research ideas in what is called the discovery phase. This step can take from three to six years. Generally, researchers will test a potential new treatment in animals before moving on to the first stage of clinical testing in humans.

How long is each clinical trial phase?

Phase 1 trials typically last several months, but less than a year. Because these trials test treatments for safety, not for effectiveness, they may only enroll healthy volunteers.

Around 70% of potential new drugs pass Phase 1 and enter Phase 2, which continues to measure safety, while looking at how effective the treatment is, too. Phase 2 trials recruit up to several hundred patients with the condition to take part. This phase typically lasts several months to two years

Just 33% of drugs make it past Phase 2 and into Phase 3, which tests the potential treatment in the largest number of people. This phase measures both safety and effectiveness with many volunteers, sometimes thousands. Phase 3 trials last from one to three years.

After Phase 3, a pharmaceutical company may submit a New Drug Application (NDA) for the treatment to the Food and Drug Administration (FDA). The FDA then reviews results from all stages of the trial to determine whether it will approve the drug and allow the pharmaceutical company to begin marketing it to the public.

Following approval, a treatment may enter Phase 4, also known as a post-marketing trial. Patients are monitored for long-term side effects of the treatment that go beyond the time frame of the other phases.

Your time commitment to a clinical trial

When you're considering taking part in a clinical trial, ask the study team about the schedule of the trial. Some trials may last for several years, but only require visits every few months, for example. Other trials may require more frequent visits, or for participants to make entries in an e-diary or paper diary in between visits. You'll want to weigh the potential benefits of participation against the time it may require of you.

If you choose to join a clinical trial, you're free to leave at any time for any reason, even before the trial is completed. Some trials also end early, if researchers aren't seeing the results they were hoping for.

The clinical trial process is long – and it's set up that way so that by the time drugs reach the public, they have been thoroughly evaluated. But the length of the process is one reason why it's so important for volunteers to take part. Without enough volunteers, up to 80% of clinical trials are delayed. Start looking for a clinical trial near you and help research move forward below.