What is a clinical trial?

A clinical trial may compare a new type of treatment to an older type of treatment, or it may compare a standard treatment to no treatment at all. Studies may also be done to gather information about a certain group of people or patients, their medical conditions, medical care, family support or feelings.

Types of clinical trials

  • Prevention: to look for new ways to prevent illness
  • Screening: to help detect diseases or conditions
  • Treatment: to test new types of treatments

Who conducts clinical studies?

Every clinical study is led by a Principal Investigator (PI), who is often a medical doctor. Clinical studies also have a research team that may include scientists, technicians, social workers, and a wide range of health care professionals.

The PI is the researcher in charge of the study and is responsible for the conduct of the study. This person agrees to conduct the study in compliance with the applicable regulations and is responsible for making sure that all members of the research team are qualified and properly trained to fulfill their roles in the study.

Many clinical trials may have a Clinical Research Coordinator.  This person works closely with the PI and manages the day to day activities of the study. Their role is to ensure participants are following the protocol. They also ensure participants understand their responsibilities, how to take the study drug or use a medical device and how to complete the trial questionnaires or diaries. They make sure trial visits, tests and procedures are scheduled on time. They also provide information about the clinical trial to staff and healthcare providers who may refer their patients to the study.

Clinical trials may be sponsored or paid for by the following:

  •  government agencies, such as the Canadian Institutes of Health Research;
  • pharmaceutical companies;
  • nongovernmental granting agencies;
  • hospitals and research institutes;
  • companies that develop medical devices or equipment; or
  • any combination of the above.

Reasons for conducting a clinical trial

In general, clinical trials are designed to add to medical knowledge related to the treatment, diagnosis, and prevention of diseases or conditions. Some common reasons for conducting clinical studies include:

  • Evaluating one or more interventions (for example, drugs, medical devices, approaches to surgery or radiation therapy) for treating a disease, syndrome, or condition.
  • Finding ways to prevent the initial development or recurrence of a disease or condition. These can include medicines, vaccines, or lifestyle changes, among other approaches.
  • Evaluating one or more interventions aimed at identifying or diagnosing a particular disease or condition.
  • Examining methods for identifying a condition or the risk factors for that condition.
  • Exploring and measuring ways to improve the comfort and quality of life through supportive care for people with a chronic illness.


Phase I: Is it safe?

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: Does it do what it's supposed to?

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: How does it compare?

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: What happens long-term?

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.