There are several phases of clinical trials, and it is useful to understand the process and progression. Here is a breakdown of the basics, although there are exceptions and overlap when it comes to final trial design:
Preclinical studies involve laboratory and/or animal investigations of a potential new drug or treatment. Mode of action and safety are tested extensively before a new drug is approved by the FDA to begin trials in humans.
Phase I trials involve the testing of a new drug or treatment in a small group of people (18-20) for the first time to evaluate safety, determine a safe dose range, and identify side effects. Participants in these studies are often healthy individuals. Phase I studies typically involve a lot of evaluations, tests and monitoring.
In phase II trials, the study drug or treatment is given to a larger group of people (100-300) to see if the therapy is effective, determine best dosing regimen, and to further evaluate safety. Often these are individuals with the particular diagnosis that the drug or treatment is targeting. Phase II trials continue with close monitoring and can also involve lab tests to measure how the investigational drug is metabolized over specific time periods.
Phase III trials are designed to enroll an even larger group of participants (1,000 to 3,000) to confirm effectiveness, monitor side effects, compare it to commonly used treatments, and collect data that will allow the drug or treatment to be used safely. These trials are often placebo-controlled and include patients with other medical problems and medications. Outcome studies typically involve many thousands of subjects over several years to evaluate the end results of a treatment in terms of illness or benefit to society.
After a drug or treatment has FDA-approval, Phase IV trials are conducted to collect additional information, including risks, benefits and optimal use. These are also known as Post-marketing trials.