Share:  
|
PAGE
MENU

What are the different phases of trials?

Clinical trials are done in four phases or stages. Each phase has a specific goal. The information gathered is used to build knowledge and support the next phase of the research process.

Phase I

A phase I ("phase one") trial is the first time that the treatment or intervention is tested in people. Phase I trials study the safety and side effects of different dosages of a treatment or intervention being studied. These trials are short, usually two to three months, and generally involve 20 to 80 participants. Often, the participants are healthy volunteers.

Phase II

A phase II ("phase two") trial finds the effects (good and bad) of a treatment or intervention under study in participants who have the disease or condition for which the treatment or intervention was developed. Phase II trials also gather information about side effects. These trials generally take one to two years to complete, and involve more participants (100 to 300).

Phase III

Phase III ("phase three") trials confirm the effects (good and bad) of the treatment or intervention under study, and compare it with the usual treatment for the disease or condition for which the treatment or intervention was developed. Phase III trials gather more information about the safety of the treatment or intervention. These trials vary in length, depending on the disease or condition being studied. They usually involve 1,000 to 3,000 participants from many centres within and outside Canada who have the disease or condition for which the treatment or intervention was developed.

Phase III trials are usually randomized. A randomized controlled trial (RCT) is an experiment in which researchers randomly (by chance) assign eligible participants (or other units of study such as classrooms, clinics or hospitals) into groups to receive or not receive one or more treatments or interventions that are being compared.

Phase IV

Phase IV ("phase four") trials are carried out after the treatment has received approval for use in Canada and is available to the public. Phase IV trials, also called post-marketing trials, may compare the treatment (e.g., a drug) to a competitor, explore additional patient populations not studied in earlier phases (e.g., the elderly), or further study any side effects. These studies usually involve the use of a treatment or intervention under real-life conditions.

Next: What are the risks and benefits of participating in clinical trials?
Previous: Why is the research study being done?