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Phases of Clinical Trials

Clinical trials are conducted in successive phases each phase being designed to answer different questions. The ultimate goal is to develop a new drug that is effective and safe.


Phase 1 : Is it safe?

Phase 1 trials are the first to involve human subjects. They are conducted with utmost vigilance to establish the basic safety and dose of the experimental drug. Although the drug has already been tested in the lab and in animals, doctors don't know yet what the side effects are in people with cancer.

These trials are carried out in specialized units in hospitals. Phase 1 clinical trials usually include a small number of people. Participants These people often have advanced cancer and have usually received all available existing treatments.


Phase 2 : Is it showing any signs of efficacy?

If an experimental treatment is found to be safe in Phase 1 clinical trials, then Phase 2 clinical trials are initiated. Phase 2 trials assess the potential efficacy of the experimental treatment. Usually, participants receive the dose set in the Phase 1 clinical trials.  At this stage, doctors are looking for a signal of efficacy. For example, does the experimental treatment help control tumour growth?

  Phase 2 clinical trials are usually conducted with a few dozen to a few hundred people.


Phase 3: Is it better than what already exists?

Experimental treatments that have shown signs of efficacy in Phase 2 clinical trials must go through a final phase before being approved (or not) by Health Canada. Phase 3 trials compare an experimental treatment to a treatment that is normally used (standard treatment). For example, doctors may want to know if the experimental treatment is more effective and safer than the standard treatment. 

Participants are randomly assigned to receive either the standard treatment or the experimental treatment. That means that neither the doctor nor the participant knows which of the two treatments the participant is receiving. A placebo may be used in some Phase 3 trials, but it is never used alone if there is an effective treatment already approved.

Most Phase 3 clinical trials involve a large number of participants. These trials are often conducted simultaneously in many sites across the country and even around the world.