The Phases of Clinical Research

Phases of Clinical Research

Clinical research is vital to understanding how a treatment will interact with the human body. However, even after years of education and regulations, research still gets a bad rap. Why? Many people equate participation to mad scientists, dark rooms and lab rats (oh my!); but this couldn’t be further from the truth! Before any treatment is made available to the public, they go through several phases of testing. Keep reading to learn more about the 4 phases of human testing.


The 4 Phases of Clinical Research

Every phase of clinical research is regulated by the FDA, with checkpoints at each step to ensure patient safety all the way. The Four phases vary in duration, number of volunteers needed, and objective.

Phase 1

This phase consists of 20-100 healthy volunteers, or 20-100 volunteers that are in good general health but have been diagnosed with the condition being studied. The phase lasts several months and tests the safety of the intervention. The main objective here is to find the best dosage level, as well as how the treatment should be given (i.e. infusion, injection, oral, topical, etc.). How the drug is processed, metabolized, and excreted is also investigated here. Phase 1 is the smallest phase since it is the first time it is being tested in humans, and it is estimated that 70% of the medications will move on to the next phase.

Phase 2

Phase 2 consists of several hundred volunteers who have been diagnosed with the condition being studied. This phase can last anywhere from several months to two years. The main objective of a phase 2 study is to test the effectiveness of the intervention. To do this, most phase 2 studies will have a control (placebo) group in which subjects are randomized, or randomly assigned. This allows researchers to gather unbiased data on whether the intervention is working or not. From here, it is estimated that only 33% of the interventions will move on.

Phase 3

This is the last phase before an intervention can be eligible for FDA approval. Phase 3 is a large-scale test consisting of 300-2,000 volunteers who have been diagnosed with the condition being studied. These studies are conducted over 1-4 years and provide the researchers and FDA a better understanding of the safety and effectiveness of the intervention over a longer period of time. This is also where the intervention will be monitored for side effects and serious adverse events. As with phase 2, these studies are also randomized and blinded to prevent data biases. It is estimated that about 25-30% of interventions pass this phase of testing. Once an intervention passes this phase, the pharmaceutical company can then apply for market approval.

Phase 4

This phase encompasses several thousand volunteers who are diagnosed with the condition being studied. Often called post marketing surveillance trials, these studies continue to evaluate the safety and effectiveness of the intervention, and long-term effects on the lives of those taking it. The cost of the intervention is also compared to other similar therapies for cost effectiveness. These findings can result in restrictions being placed on the medication, or even being taken off the market.

Volunteers at Centex Studies


Clinical research provides the knowledge on how treatments, medications, and medical devices affect the human body. Most studies at Centex are either phase 2 or 3 studies.

We realize clinical research participation is not for everyone, but safe and effective medical advancements would not be possible without volunteers like you!

If you are interested in learning more about our currently enrolling studies and how to get involved, click HERE.


Leave a Comment