What Are the Different Phases of a Clinical Trial?

Remember to ask the clinical trial coordinator about the phase of the trial and the expected risks before giving your consent to participate.

While browsing through various clinical trials, you might often come across terms like “phase of the clinical trial” or phrases like “early stage clinical trial”, “advanced stage clinical trial”. If you are one of those people who is new to the concept of clinical trials and have no idea about what the phase of a clinical trial mean, then hopefully reading this post could answer some of your questions In this post, a part of Clinical Trials Primer Series, i will try to give a quick summary of the different phases of a clinical trial.

What do we mean by phase of a clinical trial?

Clinical trials are always conducted in stages, with each progressing step validating the effect of the study drug or procedure. These stages are known as phases of a clinical trial or medical research study. The purpose and protocol followed for each phase of the clinical trial is different from the other. Thus, each clinical trial phase can at times be considered as a separate study in itself.

What are these phases of clinical trials

Each clinical trial is conducted in 4 basic stages or phases; each of these is explained in detail below:

  • Phase 1 or Early stage Clinical trials: As the name indicates this is the first phase of a clinical trial. This is for the first time that a new drug or treatment procedure is tested on humans. The purpose of this phase of medical research is to determine the safety of the test procedure and also demonstrate that the results found in the pre-clinical trials (studies done on cell cultures and animals, for example) can be duplicated on humans. Phase 1 trials do have a some amount of risk involved due to the fact that not much is known about the effects of the drug on humans. Hence, these trials usually include a select few participants (usually 20-80 or less) and the inclusion/exclusion criteria for these studies are very strict. Usually studies prefer to include only healthy volunteers for such studies. Since the amount of risk involved is high, the compensation given to the trial participants too is high for phase 1 studies.
  • Phase 2 studies: Once a drug proves to be safe for human use it is moved to phase 2 studies. The purpose of the phase 2 clinical trial is to determine the right dosage of the drug and also establish the safety of the drug on the people actually showing the symptoms that the drug is purported to cure. The volume of trial participants is gradually increased (100-300) and the drug is tested on a larger group of people, preferably those who are actually suffering from the disease condition which the drug aims to treat.
  • Phase 3 Clinical trials: Once the drug proves effective and safe in the phase 2 trial it is moved further to the phase 3 trial. These are long term trials that include a large population of participants usually trying to include the various segments of the population (men, women, children, etc.)These clinical trials intend to confirm the effectiveness, efficacy, and safety of the study drug and monitor the side effects of the drug. The basic purpose of these studies is also to verify the benefits and risks involved in the use of the new drug as compared to that of the already established modes of treatment. A drug is moved to the next phase only if the drug proves to be significantly more beneficial than established means of treatment.
  • Phase 4 clinical trials or Advanced stage trials: Also known as post marketing studies, these studies are conducted on drugs or treatments that have already got approvals and are being prescribed by doctors. These studies are basically conducted to collect extra efficacy data and market the drug as a better means of treatment than the other available methods of treatment.

How does this information matter to you as a prospective participant…well, with each progressing phase of clinical trial, the risk involved reduces. Thus phase, 1 trials are the riskiest and also pay the most (for time) whereas phase 4 trials are the safest, with proven medical benefits, (but rarely have any monetary benefits involved).

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22 thoughts on “What Are the Different Phases of a Clinical Trial?

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  20. This is a good! read. I would participate in Phase one trials.

    Your blog referrs to different Drugs or Treatment for conditions,

    does treatment mean “Chiropractic” adjustment?

    A friend, high tech mgr for Abbott Res”, had shown a site “JALR”

    Is there more? I can travel anywhere. And I like telling stories on

    myself. I need new material! I’m very healthy. Do you have a

    current list of Phase one not in JALR.org? Thank you / Joe

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