Pharmaceutical trials are divided into four phases.
Phase 1 trials
In Phase 1 clinical trials, researchers test a new drug in a small group of people (20 - 80) for the first time to evaluate its safety, determine a safe dosage range and identify side effects. This research is often conducted initially with healthy adult volunteers.
Phase 2 trials
If a new treatment is determined safe after a Phase 1 trial, it will continue to Phase 2. In Phase 2 clinical trials, the drug is given to a larger group of people (40 - 100) to determine effectiveness and safety.
Taking part in a Phase 2 study has fewer risks than Phase 1. By this point, researchers will know a lot more about the effects of the drug on humans and will be ready to test it on a larger group of patients or healthy volunteers.
During a Phase 2 study, the researcher will be looking at:
Minor side effects of the drug
How well the drug works
And possibly, alternative ways of giving the drug (i.e. injection versus tablets)
Phase 3 trials
In Phase 3 studies, the drug is given to large groups of people (more than 200) to further determine its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug to be used safely. Much more is now known about the new drug. For this reason, these trials involve a larger number of subjects - often hundreds or even thousands - from many different hospitals.
The main purpose of Phase 3 studies is to compare the new drug with the most commonly used existing treatment.
Researchers may want to find out:
Whether the experimental drug is more effective than the existing treatment
Whether the experimental drug has more or fewer side effects than the existing treatment
The long-term benefit of the experimental drug to a subject
Whether a subject's quality of life is changed by the experimental drug
Phase 3 studies are always randomized. This means splitting patients into two or more groups, each of which will receive a different intervention. The purpose is to compare the new drug to existing treatments for the same condition.
Phase 4 trials
Phase 4 studies are conducted after the drug has been approved to be marketed by the Food and Drug Administration (FDA). These studies continue testing the drug to collect information about its effect in various populations and any side effects associated with long-term use.
Once the three phases of a clinical trial are complete, the FDA reviews information from all the studies to see if the drug can be approved.
If the FDA approves it, the new medication will go on sale. At this point the pharmaceutical company might fund a Phase 4 trial. The main purpose of this type of trial is to promote the drug and bring it to the attention of more doctors. There are few risks involved in a phase 4 trial because much is already known about the treatment. This kind of trial is of less scientific importance than earlier phases.