Types of clinical trials

The U.S. National Institutes of Health (NIH) classify clinical trials into five types:

• Treatment trials are the most common type of trial, testing experimental treatments, new drug combinations or new approaches to surgery or radiotherapy.
• Prevention trials test new ways to prevent disease in people who have never had the disease or to prevent the disease from returning in those previously treated.
• Screening trials test the best way to detect a disease.
• Diagnostic trials are conducted to find better tests or procedures for diagnosing a disease.
• Quality of Life trials (or Supportive Care trials) explore ways to improve the comfort and quality of life for people with a disease.

Clinical trial phases

New treatments must go through three “phases” of trials before they can be considered for use;

• A Phase I trial is the first study of the experimental treatment that involves humans. Safety and dosage range are tested and side effects identified. Only a small number of people are involved.
• A Phase II trial involves a more detailed evaluation of effectiveness and safety. A larger number of people are required for a Phase II trial.
• A Phase III trial involves formal comparison of the experimental treatment with the current standard treatment to work out which is best.

People are randomly selected to receive the experimental treatment or the current standard treatment. A much larger group of people is involved.

In a Phase III trial, random treatment allocation is necessary so that each group has a similar mix of people to ensure the treatments can be compared without bias. Neither you nor the trial staff can choose which treatment you will receive. If the trial involves a new drug, it is possible that you and the trial staff might not be told which treatment group you are in; this is known as blinding and is used to prevent bias. In some trials experimental treatments are compared with a placebo, an inactive pill, liquid or powder that has no treatment value. You will be informed if the trial you are considering is blinded or placebo controlled.