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The Four Phases Of Clinical Trials: Step By Step Information

Updated: Apr 20, 2018

Clinical trials are incredibly important parts of the development of medications, medical devices, and similar products. These trials are conducted to make sure that these medical inventions are safe and effective. The are four phases of clinical trials, and each of them involves different things. This post covers every step in a simple, easy-to-understand way.


Phase One or Phase I of a clinical trial is when a product or medication is tested on humans. During this trial, only a small number of research participants are used. The number is typically somewhere between 20 and 100 people. These volunteers consent to test medication and medical products. In many cases, volunteers for these trials must be healthy individuals.


Phase I clinical trials are used to test the safety of the medicine or product. The tolerability of the drug is observed during this time, too. Research participants are often required to stay within a clinic during the research period. This is so that they can be monitored on a full-time basis. In most cases, participants are given different dosages of the same medication.


Phase Two or Phase II studies often contain two parts - Phase IIA and Phase IIB. Phase IIA is used to determine what dosing requirements should be used for a drug. Phase IIB is used to determine how effective a drug is in the different dosages from Phase IIA. Not all Phase Two trials are broken into two parts; some of them combine dosage and efficacy tests.


Phase Two trials use volunteers with certain illnesses or disorders to determine efficacy. For example, cancer patients may volunteer to test a new drug to treat a specific type of cancer. Many Phase Two trials do not go past this second stage. In 2008, reports stated that only 18 percent of Phase Two trials continued on to Phase Three trials.


Phase Three or Phase III often occur while a submission for the drug is pending at a regulatory agency such as the FDA. Trials are performed at this stage so that patient volunteers can continue receiving the drug. Additionally, this phase of trials is used for something known as label expansion. Label expansion shows whether or not the drug can treat additional illnesses or disorders aside from the original purpose.

Phase Three clinical trials use much larger groups of people than the other stages. In many cases, several hundred patients and research participants will take the drug. The clinical trials may be spread across the country in different research clinics. This helps researchers get the most accurate data possible.


Phase Four or Phase IV is often referred to as the trial for postmarketing surveillance. It is the last of the phases of clinical trials. This phase occurs to survey the safety of the drug once the FDA or a similar agency gives permission for the drug to be sold. This part of the clinical trial is also used to discover any potential rare or long-term side effects among a broad pool of patients. In most cases, this final trial may last two years.

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