The 4 Phases of Clinical Trials and How They Work

Clinical trials are studies that test new medical interventions, such as a new type of drug, surgery, or medical device, on human volunteers. They aim to determine whether the new treatment option is safe and effective. 

There are four stages of a clinical trial.

Clinical trials happen in phases. Researchers use each phase to determine if the treatment is safe and effective. If your healthcare team recommends that you participate in a clinical trial, they will explain the trial’s purpose and current phase. Most study volunteers participate in one phase rather than all four. 

Phase 1

Objective: To test a drug or treatment for the first time to learn if it’s safe and identify side effects

Number of participants: 20-80 people

How it works: Researchers usually conduct Phase 1 clinical trials on healthy volunteers. The goal is to learn how the new drug or treatment interacts with the body and determine if it is safe enough to progress to a Phase 2 trial. 

Length of time: Several months

Benefits of participating: Because most Phase 1 clinical trial participants are healthy volunteers, they may not personally benefit from the trial. Instead, they are helping advance medical research for future patients. If the clinical trial is testing a new cancer treatment, people with that specific type of cancer may also participate. This may allow them to receive new treatments before they are available to everyone. 

Risks of participating: There is a risk of side effects during Phase 1 clinical trials because researchers do not yet know which dose of treatment a person can tolerate without side effects. Study participants are monitored closely for any side effects during a Phase 1 trial. 

Treatments that make it past Phase 1: About 70%

Phase 2

Objective: To determine the efficacy of a drug or treatment, and to continue studying the safety

Number of participants: 100-300 people

How it works: Researchers administer the new medical treatment to people with the disease or condition the treatment is trying to target. The goals of a Phase 2 clinical trial are to determine if the treatment is effective and to gather more safety data. Researchers use the data from Phase 2 trials to refine their research questions and alter the treatment if needed. 

Length of time: Several months to two years 

Benefits of participating: If the treatment is successful, you may experience benefits to your condition. 

Risks of participating: A Phase 2 clinical trial is not large enough to determine whether the treatment is safe or effective, and there is still a risk of side effects. Researchers closely monitor participants for any side effects or health changes during a Phase 2 trial.

Treatments that make it past Phase 2: About 33%

Phase 3

Objective: To confirm the treatment’s effectiveness, evaluate for side effects, compare it with standard or similar treatments, and collect information that will allow it to be used safely

Number of participants: 1,000-3,000 people

How it works: A Phase 3 clinical trial is also known as a pivotal trial. During this stage, researchers will compare the new treatment with current treatments to determine if it is more effective or better tolerated in people with the disease or condition. If the treatment is found to be safer or more effective than other options, the United States Food and Drug Administration (FDA) can choose to approve the treatment. 

Length of time: 1-4 years

Benefits of participating: Study participants either receive the new treatment or an existing treatment option. Regardless of which treatment group you are placed in, you will receive a treatment developed specifically for your disease or condition. 

Risks of participating: There are risks to participating in a Phase 3 clinical trial because researchers may learn of new or rare side effects during the study. However, to reach Phase 3, a new treatment must be proven safe through the first two phases. Before joining a Phase 3 trial, ask the researchers what side effects they observed in the earlier phases. 

Treatments that make it past phase 3: About 25-30%

Phase 4

Objective: To track the drug or treatment’s safety and seek more information about its benefits and best uses

Number of participants: Available to the general population

How it works: Once approved, the FDA will continue to monitor the treatment in what is known as post-market safety monitoring. The goal is to determine if people receiving the treatment develop any new side effects over time. 

Length of time: Varies 

Benefits of participating: The new drug or treatment has already proven safe and effective for the general population.

Risks of participating: While there is a risk of side effects with any treatment, Phase 4 treatments are considered safe for most people since the safety was cleared in Phase 3.

People participate in clinical trials to help others and potentially receive the latest treatments for their health conditions. 

If you would like to learn about participating in a clinical trial, talk with your healthcare provider. Your treatment team can recommend specific trials and assist you with the application process.

When considering a clinical trial, keep in mind the following factors:

• Purpose: Ask questions to understand the trial’s purpose and how it will benefit the participants and future patients. 
• Time: Find out how much time, effort, and travel are expected to participate in the trial. Ask questions about the experience to understand the schedule, location, and requirements. 
• Discomfort: Some medical interventions cause pain or discomfort. Ask questions about what the treatment will feel like and determine how much discomfort you are willing or able to tolerate. 
• Risk: All medical treatments involve some risk. Before joining a trial, the researchers should explain the risks involved. 
• Oversight: In the U.S., an Institutional Review Board (IRB) monitors most clinical trials. The IRB is made up of medical doctors, researchers, statisticians, and other community members. Their goal is to ensure the safety of study participants. Before joining a clinical trial, ask the researchers if an IRB is monitoring the study. 
• Cost: Ask the research team if there is a cost to join the study. Health insurance may cover some or all of the cost. Request a written cost estimate, and talk with the hospital billing department and your insurance company to determine if you will be responsible for any of the charges. 

Once you have considered the clinical trial’s purpose, requirements, risks, and benefits, talk with your healthcare provider to determine if you would like to join the trial. Before participating, the researchers will ask you to sign an informed consent document, stating that you understand the trial and its possible risks.

Remember, participating in any phase of a clinical trial is voluntary. You can leave at any time. 

Clinical trials use human volunteers to evaluate new medical treatments. Clinical trials have four phases.

The first three phases determine if the treatment is safe and effective before it is available to the general public. The last phase studies the treatment once it’s approved and used by the general public.

If you are interested in participating in a clinical study, find out which phase the study is currently in. Each phase has different benefits, risks, and enrollment needs.