Clinical Trial Phases: What are Clinical Trial Phases?

What are Clinical Trial Phases?

In order to reach patients, every drug must make its way through four clinical trial phases. Each clinical trial phase has a different goal and separate hurdles to clear before a potential new treatment can move forward.

The process begins when researchers develop new treatments in the lab. When they're ready to try to bring the treatment to market, researchers submit data to the FDA for approval to continue research. The preclinical research stage may involve testing to see if a drug is safe to use in animals before human testing begins. Once approved, researchers or a pharmaceutical company can begin enrolling volunteers in a phase I trial.

What are the Phases of Clinical Trials?

Phase I

Phase I clinical trials test whether drugs are safe to use in humans.

This trial phase can last anywhere from several months to a year. These trials are typically small -- just 20 to 100 volunteers. Some phase I clinical trials only look for healthy volunteers, who may be compensated for participating. Others accept those with the condition the drug aims to target. While the drug may help symptoms, a phase I trial’s goal is only to prove safety.

Doctors start the trial by administering a very small dose of the drug and measuring how it's absorbed, metabolized and excreted in the body. Researchers also check for side effects. As researchers increase dosage, they continue to measure side effects. If researchers find the drug to be safe enough, it then moves forward to phase II. Around 70% of experimental drugs move past this stage.

Phase II

Phase II clinical trials test the effectiveness of a drug or medical device. This stage can last from several months to a few years, and generally involves several hundred participants.

Most phase II clinical trials are randomized, which means one group of participants receives the study drug, while the other group receives a placebo or an existing, standard treatment.

Many phase II studies are "blinded," which means that neither the researchers nor the participants know who received the study drug.

In this phase, the drug has to be found effective in order to move forward to the largest phase, phase III.

Phase III

Phase III clinical trials are typically the largest. They involve anywhere from several hundred to several thousand participants in a randomized, blind study. This testing phase can last several years as the FDA gathers thorough data about the drug's effectiveness and potential side effects.

Once a treatment or device makes it through this stage, a pharmaceutical company can request FDA approval to start marketing the drug. That request is called a New Drug Application (NDA).

The FDA decides whether or not to approve the drug based on their review of clinical trial results. Sometimes, it may require that additional studies be done or that a hearing be held to decide whether a drug’s benefits outweigh its risks. If all looks good, the drug is approved and the pharmaceutical company can bring it to market.

Phase IV

Also known as Post Marketing Surveillance Trials, Phase IV trials take place after a drug or device has been approved. In this phase, pharmaceutical companies monitor a drug's long-term effectiveness and impact, compare it to existing trials in the market, and determine the cost effectiveness of the new treatment.

This phase is important because it may take a few years for longer-term side effects to appear.

How Do I Join a Clinical Trial?

There are thousands of clinical trials looking for volunteers across disease areas. Search for a trial in your area to find one that's a match for you.