The Five Phases of Human Clinical Trials

The Five Phases of Human Clinical Trials
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  • 1:45 Phase 0
  • 2:30 Phase 1
  • 3:25 Phase 2
  • 4:40 Phase 3
  • 5:30 Phase 4
  • 6:15 Lesson Summary
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Lesson Transcript
Instructor: Dana Dance-Schissel

Dana teaches social sciences at the college level and English and psychology at the high school level. She has master's degrees in applied, clinical and community psychology.

Human clinical trials help us understand the effectiveness of a treatment. This lesson will discuss the five phases of human clinical trials and will end with a brief quiz to test what you have learned.

What Is a Clinical Trial?

How many times in your life have you had a cold? Probably at least a few, right? We all know the annoying symptoms that we sometimes feel when we have a cold such as a stuffy nose, sore throat, and body aches. Do you use medication or other treatments when you get a cold? Most people do seek relief from the symptoms of a cold with some sort of treatment to help them feel better. How do we know which treatments work? We can thank clinical trials for this knowledge.

Researchers use clinical trials to test out new treatment options. Clinical trials help researchers understand which treatments work and the risks that may be associated with their use. Human clinical trials test these potential treatments on human beings who agree to participate in the research. There are five phases of human clinical trials. The earliest phases of human clinical trials usually focus on potential side effects of a given treatment while later phases aim to assess efficacy of the new treatment compared to current treatment options.

Not all phases of a human clinical trial will necessarily be carried out if a potential treatment presents unexpected outcomes. It is important to understand that while the overall clinical trial focuses on testing just one treatment, each individual phase is essentially a separate study with different participants. Therefore, the phases described below usually take place over a long period of time and each phase builds upon the information learned from the previous phase.

Phase 0

The first phase of a human clinical trial is Phase 0. This is the earliest point of testing out a potential treatment on people. During phase 0, researchers are trying to figure out if the treatment acts the way they expect it to. For example, to use our earlier example of cold medicine, if the treatment they are testing out was designed to clear a stuffy nose and fails to do so during phase 0, the researchers might decide to try to something else. Usually, there are very few participants in phase 0 of a human clinical trial and they typically don't receive a therapeutic dose of the potential treatment. Again, the goal in this phases of a human clinical trial is to make sure that the treatment is doing what it was designed to do.

Phase 1

Phase 1 of a human clinical trial takes place after the researchers are sure that the treatment behaves as they expect it to in human beings. This phase usually has a few more participants than phase 0 and may occur in stages. For example, if the first group of phase 1 participants does well with the treatment, the researchers may add a few more people. In addition, as with phase 0, the starting dose or amount of the potential treatment is usually small. Participants are closely monitored for potential side effects and unexpected outcomes. The dose is slowly increased with future groups in this phase to work toward a safe and therapeutic dose.

Let's go back to the cold medicine. Once we know that a given treatment works, how do we know how much to take? Chances are, this was determined during a phase 1 human clinical trial.

Phase 2

Phase 2 in a human clinical trial is usually made up of a much larger group of participants. In this phase, researchers are still playing with the dose a bit and looking for potential side effects. Researchers may also compare the new treatment to another treatment that has been used effectively in the past. This comparison helps them learn more about how the new treatment works and if it is more effective than other treatments.

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