Clinical Trial Phases & Stages

When a new medication is developed, the process starts in a test tube and then progresses to animal studies. These early studies give researchers an idea of whether a medication may work and what kind of side effects it might have in humans. In the same way, when developing a new behavioral therapy, procedures delivered in the therapy are tested very early in the process to see if they are helpful. If the results of early studies look promising, clinical trials are conducted to test the medication or behavioral therapy treatment in people. Medication trials are divided into phases. Similarly, behavioral therapy trials are divided into stages.

Phases of Medication Trials

Phase I
Question: Is the treatment safe?
Risk: Riskiest—First trials in humans
Purpose: These studies determine safety of a drug in a healthy volunteer.
Length: Shortest—A few weeks to a few months
Number of Participants: Approximately 20—80 participants

Phase II
Question: Does the treatment work?
Risk: Moderate—Some safety information about the drug is already known.
Purpose: The purpose is to determine the efficacy of a medication.
Length: Medium—A few months to a year or more
Number of Participants: Approximately 100—300

Phase III
Question: What are the long-term results in lots of people?
Risk: Lowest—More information about safety and effectiveness is known.
Purpose: These studies are looking at efficacy and safety in a larger group over a longer period.
Length: Longest—Often a year or longer
Number of Participants: Approximately 1,000—3,000

Stages of Behavioral Trials

Stage II
Question: Does this behavioral therapy work?
Purpose: The purpose is to determine the efficacy of the behavioral therapy.

Stage III
Question: Can this behavioral therapy be widely used?
Purpose: These studies are looking at efficacy and safety in a larger group over a longer period.