Clinical Trial Phases: The Steps in Medical Research & Drug Trials

In order for a new medical intervention (medication or treatment) to be approved for use in humans it must undergo a series of steps to assure its safety and efficacy. In order to be approved by the FDA new treatments must go through this series of steps in order. This process is expensive and time consuming. Additionally, a huge majority of potential interventions will not pass all phases of the clinical trial.


“Pre-Clinical” Research = basic science research done before there is any testing on human subjects. This can include in vitro bench work (study treatment in test tubes or on cell cultures) or in vivo (in animals).


Phase 1 Clinical Trial = Researchers give the treatment to a few dozen at multiple different dosages individuals and monitor side effects. Basically you are just making sure the drug isn’t super dangerous before you give it to more people in the next phase. Participants in this type of study often don’t even have the disease of interest.


Phase 2 Clinical Trial = Researchers give the treatment to a small group (usually a couple hundred) of people with the disease of interest to determine if the drug might work and/or what the best dose might be. There is no randomization or control group in this phase so conclusions are tentative at best.


Phase 3 Clinical Trial = Researchers give the treatment to a large group (usually 1000s) of people with the disease to determine “definitely” if the drug works. This step includes a control group, randomization and blinding.


Phase 4 Clinical Trial (AKA Post Marketing Surveillance) = After the drug has been approved by the FDA and released on the market the occurrence of side effects continue to be monitored. When a drug is released to the public it is often given to hundreds of thousands of patients. Therefore, this phase of the trial allows for the detection of rare complications that may be missed in the smaller phase III trial. Phase IV trials can also better identify long term complications, because they are longer than Phase III trials. Unlike the other phases of clinical trials, Phase IV Trials are carried out by community physicians rather than researchers. Rather than a small number of dedicated researchers organizing this phase, all providers who prescribe the treatment should be on the lookout for complications and report any side effects that may be attributable to the intervention.

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