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About Clinical Trials

Clinical trials are research studies that explore whether a medical device, treatment or strategy is safe and effective for humans.

Clinical trials are essential for the development of safe and effective treatments

A clinical trial is a research study designed to answer specific questions about a new treatment or a new way of using a current treatment. They help researchers and doctors build their knowledge, better understand human diseases, conditions and injuries and establish whether potential treatments are safe and effective. 

In this section:

Clinical trials are a critical part of clinical translation, the process by which science becomes medicine. Learn more about clinical translation here.


How clinical trials work

Clinical trials are designed to help researchers answer specific questions. The fact that a procedure is experimental does not automatically mean that it is part of a research study or clinical trial. Trials typically begin with the development of a clinical protocol, which outlines how the trial will be conducted, including the objectives, design, methodology and organization. The design looks to eliminate bias on the part of the participating researchers and doctors.

A clinical trial often includes a comparison to determine whether or not the treatment is having an effect. Participants in the experimental arm, or test arm, of a trial receive the treatment, and those in the control arm receive no treatment, a placebo or the standard of care.

Participation in a clinical trial may be randomized, meaning participants are randomly assigned to either the experimental or the control arm. In an open label trial, both the participants and the investigators know who is in the experimental and control arms. In a single-blind trial, participants don’t know whether they are getting the test treatment or not but the investigator does know. In a double-blind trial, neither the participants nor the investigators know who is in the test or the control arm. This helps to reduce bias on the parts of those conducting the trial and double-blind trials are therefore considered the most reliable.

Sometimes, in attempting new surgical techniques or where a disease or condition is rare, test treatments may be tried on just one or two people outside the confines of a clinical trial. In these cases, standard patient protections should still apply.


The phases of clinical trials

Clinical trials typically start with a small number of people and are focused on testing safety. As the procedures are perfected and the risks evaluated, the number of participants is gradually increased and the effectiveness of the treatment is more closely examined. The steps through which trials progress are called phases. While the terminology might vary between countries, the idea of a progressive building of knowledge remains consistent.

  • Phase 1: Is it safe?
    Researchers test a new drug or treatment in a small group of people for the first time to evaluate its safety, determine a safe dosage range and identify the most frequent side effects.

  • Phase 2: Is it safe enough to continue testing and does it work?
    The drug or treatment is given to a larger group of people to see if it is effective and to further evaluate its safety.

  • Phase 3: Does it work for an even larger group of people?
    The drug or treatment is given to large groups of people to confirm its effectiveness, monitor side effects, compare it to commonly used treatments and collect information that will allow the drug or treatment to be used safely.

  • Phase 4, Long-term follow up: What are the long-term benefits and risks?
    Studies are done after the drug or treatment has been marketed to gather information on the drug's effectiveness in various populations and any side effects associated with long-term use.


Variations by country

The structure of the clinical trial process varies from country to country, as do the laws and regulations governing trials and the standards of proof required for the approval of new treatments. However, reputable clinical trials follow a process similar to that illustrated above and generally have these things in common:

  • Respect for participants’ rights and protection for their well being
  • Evidence-based treatment supported by lab research with cells, tissues and animals
  • Approval, review and oversight by an independent committee, board or agency
  • Compliance with appropriate laws and regulations concerning research on human subjects
If you are considering participating in a clinical trial, these are things to consider.