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What are the Phases of Clinical Trials?

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While preclinical lab research provides a solid foundation of information about how a drug may work and its safety, it is not a substitute for studies that show how the drug will interact with the human body.


"Clinical research" and "clinical trials" are studies conducted in people. They follow a rigorous series of testing from early, small-scale, Phase 1 studies to late-stage, large scale, Phase 3 studies. If a treatment is successful in one phase, it moves on to the next phase. A successful clinical trial process continues until the developer files an application with the U.S. Food and Drug Administration (FDA) or a regulatory agency for the medication to be approved and prescribed to humans.


Below is information on the specific phases of clinical trial research.

Trial Phase Details

Phases of clinical trials

Phase I: Tested on healthy participants to find out whether a medical approach (e.g., drug, diagnostic test, device) is safe, identify side effects, and figure out appropriate doses.

Number of people: Typically fewer than 100


Phase II: Start testing on participants with the disease or condition to see whether a medical approach works. Continue monitoring for side effects; get information that goes into designing a large, phase III trial.

Number of people: Typically 100-300


Phase III: Tested on participants from patient populations for which the medicine is eventually intended to be used. They are assigned to receive either the medication being evaluated, a current standard of care treatment or a placebo to prove whether a medical approach works; continue monitoring side effects.

Number of people: As many as needed or able to enroll—can be 1,000 or more


Phase IV: When a medical approach or drug is being marketed, continue gathering information on its effects.

Number of people: Thousands


Insight Clinical Trials is one of the leading independent medical research institutes in Northern Ohio. With our patients and their families as our first priority, we are dedicated to safe research specializing in mental health conditions such as depression, anxiety, ADHD, Alzheimer’s disease, dementia and other neurological disorders. Our team of medical experts stands ready to help participants access the latest medical interventions and healthcare.

Contact us today to learn more about what our clinical trials are, and any questions you may have.


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