by Wood D

research lab study After thoroughly investigating drugs or other treatments using laboratory animals, researchers design studies, called "clinical trials." The purpose of these trials is to test the treatments' safety and effectiveness in people. To receive approval from the United States Food and Drug Administration (FDA) for a new drug, manufacturers must prove that the agent works in humans and is not dangerous. They do this by submitting results from a series of clinical trials.

Many Phases of Study

Clinical trials involve a multiphase process, which usually follows this pattern:

The first phase typically lasts around 18 months. It tests the safety of using the drug in humans and only enrolls a small number of volunteers. Healthy people usually participate and can tell researchers if they experience side effects. Blood levels of the drug are often measured so that scientists can estimate a likely effective dosage.

If new drugs are deemed safe, they move on to Phase II. This phase helps give an early indication of whether a drug will be effective. It is designed to establish what test conditions will be needed in Phase III to ultimately demonstrate a treatment's effectiveness. By using drugs in various combinations of dosages, researchers decide on what the best dose and timing of the treatment will be for the final phase of testing. Phase II typically involves a relatively small number of patients and lasts about two years. Phase II studies may or may not involve a “control” group of patients who receive only a non-active placebo.

Drugs that pass Phase II move on to Phase III. In this phase, researchers compare the agent to the current standard of treatment or a placebo, an inactive ingredient. This phase lasts 1-4 years and will ultimately determine whether the treatment is effective. Depending on the disease studied, hundreds or even thousands of people may be enrolled.

Double-Blind Studies

In a double-blind study, neither the participants who are enrolled nor their doctors are told which drug or treatment the participant is receiving. Double-blind studies typically occur in Phase II and III trials.

Who Is Eligible for Clinical Trials?

Eligibility criteria for clinical trials are stringent so that scientists can measure results with fewer complicating factors, such as previous treatments or medications taken for unrelated conditions. But finding enough people who meet those requirements takes time, often several years.

Using the Internet to Recruit Participants

The National Institutes of Health (NIH) clinical trials website is a searchable database that aims to bring together scientists and potential trial participants. Patients, families, or physicians can easily hunt through thousands of trials to find ongoing or completed research related to a specific condition. You can browse through a list of diseases or trial locations, or let the site narrow it down through a focused search.

"The goal is to have people come to one site," says Alexa T. McCray, PhD, director of biomedical communications for the National Library of Medicine. "People were having trouble finding the information they needed."

Considering a Clinical Trial

Dr. McCray suggests you do the following when considering participating in a clinical trial:

  • Consult with your physician.
  • Review and fully understand everything contained in the informed consent, a document that outlines key facts and the potential benefits and risks.
  • Ask questions, such as:
    What procedures are involved?
    How long will the treatment take?
    How often must I go to the hospital or study site?
    What should I avoid while participating?
    Can I continue taking other prescription drugs during the trial?
    What will be expected of me overall?

Keep in mind that the medication or treatment being tested in a trial may have unexpected or unpleasant side effects. The regimen may also be complex and hard to follow. However, patients can withdraw at any time after enrolling.


AIDS Clinical Trials Information Service 

Cancer Trials National Cancer Institute 

United States Food and Drug Administration 


BC Cancer Agency 



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Joffe S, Weeks JC. Views of American oncologists about the purposes of clinical trials. J Natl Cancer Inst. 2002;94(24):1847-53.

Zivin JA. Understanding clinical trials. Scientific American. 2000:69-75.