What is a clinical trial?

Written by: Jennifer He

You have recently been told by your primary care provider or specialist that you qualify for a clinical trial. After browsing through some studies, you realize that the process can be quite confusing. You might be asking yourself, “What, exactly is the purpose of a clinical trial?”, “What are all of these ‘phases’?” and “Why must I meet these ‘inclusion criteria’ to be able to participate?”

Simply put, a clinical trial is a study that compares the effects and value of a new or repurposed intervention (e.g., medical treatment or device) against a control (e.g., current standard-of-care) in human subjects. Evaluating an intervention is a lengthy, resource-intensive process that is usually done in phases. Using a novel drug as our example, the four phases commonly seen in clinical trials will be explained.

Phase I — At what dosage is this drug considered safe?

Purpose: To examine how the body processes and interacts with the drug, as well as how much the body can safely tolerate.

Participants: Usually, a small number of healthy volunteers, but may also involve patients who have tried and failed on existing standard therapies.

Phase II — Does this drug work under ideal conditions?

Purpose: To evaluate the effects of various drug doses on patient disease under a strictly controlled environment. This is done by looking at a patient’s less definitive clinical outcomes, like tumor shrinkage rather than survival, and on minor safety signals, like minor bleeding.

Participants: A larger number of patients than phase I, but not quite large enough to provide strong, conclusive evidence for the drug. These participants are carefully selected with narrow inclusion criteria.

Phase III — Does this drug work under ‘real-world’ conditions?

Purpose: To look at the value of an intervention in clinical practice. In this phase, the drug will typically be compared against the current standard-of-care.

Participants: Hundreds or even thousands of patients. The inclusion criteria that needs to be met is broader than in phase II. Participants are usually randomly placed in either the treatment or control group.

Phase IV — Does this drug have long-term adverse side effects?

Purpose: To study the long-term safety, effectiveness, and benefits after the drug has been approved and available on the market.

Participants: Large populations of the general public, special patient populations (e.g., pregnant women) or long-term follow-up of phase III trial participants.

Though each step is necessary, it is important to note that not all studies you come across will fit neatly into these categories. Many will combine aspects of different phases and can be thought of more broadly as early phase studies and late phase studies.

For more information on clinical trials available to treat, diagnose and manage disease, click on our website link: www.healmary.com

The content on this site is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Please seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

References

Friedman, L. M., Furberg, C. D., DeMets, D. L., Reboussin, D. M., & Granger, C. B. (2015). Fundamentals of Clinical Trials (5th ed.). Cham: Springer.