Clinical trials are experiments that use human subjects to answer a scientific question. Uses of clinical trials include testing if a new therapy is safe to use or if it is more effective than the standard treatment for a disease. It is important to note that there are risks associated with all new medical treatments, so clinical trials are carefully designed and are very carefully regulated by government agencies to ensure that the health and welfare of patients are protected. In Canada, this regulation is overseen by Health Canada; in the United States, the regulating body is the Food and Drug Administration (FDA).

Clinical trials that are used in the development of new treatments are generally divided into stages or phases:

• Phase I – Usually involve a small number of patients to test the feasibility and safety of a new therapy or treatment.
• Phase II – Continue to test a therapy’s safety but also begin testing the effectiveness of the therapy. Phase II trials are usually only slightly larger than Phase I trials.
• Phase III – At this stage the number of patients in the trial is increased and the main focus is understanding how effective a new therapy is as a treatment for the disease.
• Phase IV – Once a therapy has been approved by the health regulator, such as Health Canada, and is available through commercial means, this phase can be used to perform a longer-term study of the treatment risks and benefits in a much larger group of patients.

Many potential new treatments do not advance beyond Phase I or II for a variety of reasons, including identified safety concerns, lack of efficacy compared with currently approved options, or costs associated with the trial and/or treatment itself.

Participating in a Phase I, II or III clinical trial is not a way to receive treatment as it is uncertain whether the intervention being tested in the trial is effective, and it is not guaranteed that you will receive the new therapy or intervention, specifically in Phases II and III (i,e., you may be given the placebo). Only about 1 in 10 interventions brought to a phase I trial become a commercial product. Rather, clinical trial participation offers patients a more active role in research and permits patients to make a valuable contribution to the development of potential new therapies.