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Learn About Clinical Trials

If you’re thinking of joining a clinical trial, find out about the different types of trials, the benefits and risks, and what to expect when you participate. 

What are clinical trials for?

Clinical trials are how researchers test the safety and effectiveness of new:

  • Medicines
  • Procedures, like surgeries
  • Tests for diseases
  • Strategies to prevent diseases, like vaccines or special diets

In many cases, clinical trials are conducted to see if one treatment strategy is better than another one. The U.S. Food and Drug Administration also requires a series of clinical trials to be conducted to make sure a new medicine or device is safe and effective before approving or clearing it for use.

What are the types of clinical trials?

There are 4 types of clinical trials, called phases. Most new treatments go through 3 phases of clinical trials before the FDA approves them.

  • Phase I (phase 1) clinical trials test a new treatment in a small group of people to see if it’s safe and if it causes any side effects.
  • Phase II (phase 2) clinical trials test the treatment in a larger group to see if it works (if it’s an effective way to discover, treat, or prevent the disease).
  • Phase III (phase 3) clinical trials test the treatment in a very large group to see if it works better than what doctors are already using. Treatments need to pass phase III trials to get FDA approval.
  • Phase IV (phase 4) clinical trials help researchers continue to learn about a treatment after the FDA approves it.

What happens during a clinical trial?

First, researchers find a certain number of volunteers who meet the trial’s eligibility criteria — the guidelines for who can and can’t participate in the trial. For example, a trial might need volunteers who are a certain age or have a certain disease or health condition.

The volunteers sign a document called an informed consent. It explains the details of the trial and makes sure that volunteers understand the risks and agree to all the rules.

The gold standard for research is a randomized clinical trial (RCT). In an RCT, researchers randomly assign volunteers into 2 or more groups:

  • The treatment group gets the new treatment, test, or preventive care. Sometimes there is more than 1 treatment group in an RCT.
  • The control group can get no treatment, the standard treatment that doctors already use, or a placebo (a fake treatment that’s harmless but doesn’t work).

When possible, researchers make the trial double-blinded. This means that the volunteers don’t know whether they’re in the treatment or control group, and neither do the researchers. That way, the results won’t be affected by what the volunteers or researchers think or feel about the treatment.

Depending on the trial, volunteers may need to do different things, like take pills or get eye exams. Volunteers usually need to come back for follow-up visits over several months or years, so researchers can see how the treatment, test, or preventive care works over time.

What are the benefits of joining a clinical trial?

By joining a clinical trial, you can be one of the first people to get a new treatment. If the treatment works, it could make your vision clearer, help treat your eye disease, or help prevent other people from getting your eye disease.

You can also help improve care for countless people in the future. If you have an eye condition that runs in your family, the trial could help find better treatments for your family members.

What are the risks of joining a clinical trial?

Because the treatment, test, or preventive care in a clinical trial is new, researchers don’t know exactly what the risks are. The treatment itself may harm you, or you may get side effects.

A team of doctors, nurses, and support staff will give you checkups to find any side effects and make sure you’re healthy enough to stay in the trial.

An independent group of experts will also monitor the trial. If the experts find that the risks of the new treatment outweigh the benefits, they stop the trial right away. For example, if volunteers get severe and unexpected side effects, this group of experts may recommend stopping the trial.

What if I want to leave a clinical trial?

Volunteers have the right to leave a trial at any time, for any reason. But if too many people leave a trial, the researchers may not be able to get any results — so it’s important to only join a clinical trial if you think you’ll be able to stay in it until the end.

If you get serious side effects or develop a new health problem during the trial, the researchers may recommend that you leave the trial. Your health always comes first.

What does it cost to join a clinical trial?

Volunteers who join clinical trials at the NEI Eye Clinic in Bethesda, Maryland pay nothing for their participation, and they may qualify for support with travel expenses and other related costs. Other sponsors may include:

  • Other U.S. Federal agencies
  • The company that makes the treatment or test
  • Individuals
  • Universities
  • Organizations

Sponsors cover the costs of the clinical trial. But before you join a trial, ask the trial staff about costs for you. Then check with your health insurance company to see if your plan will cover any costs that the sponsor doesn’t cover.

A warning about stem cell clinics

Every day, researchers are learning new things about how stem cell treatments can help with eye health and vision loss. But some stem cell clinics are already advertising these treatments as “miracle cures” — without knowing if they work or if they’re safe. And they may charge thousands of dollars for these unproven treatments, which aren’t covered by insurance.

If you’re interested in getting stem cell treatment, talk to your doctor about it. They can help you understand if the treatment could be right for you. And they can find out if the treatment is FDA-approved or if there’s a clinical trial you can join.

What rights do volunteers have?

People who volunteer to participate in clinical trials have the right to:

  • Ask questions about the trial
  • Leave the trial at any time
  • Keep their medical information private and stay anonymous in reports about the trial

Volunteers also have the right to know things about the trial, including:

  • Risks, benefits, and costs of the trial
  • What they will need to do during the trial
  • Where the trial will happen and how long it will last
  • How researchers will use volunteers’ private medical information
  • Any new information about the treatment that researchers find during the trial

After the trial is over, volunteers also have the right to know whether they were in the treatment group or the control group.

How do I know if a clinical trial is right for me?

Joining a clinical trial is a big decision. Talk with your doctor about the risks and benefits. Together, you can decide if a clinical trial is right for you.

It’s also important to ask questions and make sure you understand what’s expected of you before you volunteer.

Clinical Trials in Vision Research: Information for Volunteers

If you're thinking about taking part in a clinical trial, this Clinical Trials in Vision Research booklet will help answer your questions. This booklet has information about clinical trials at NEI and questions to ask before participating in a trial.

Download the Clinical Trials booklet:

Last updated: June 29, 2023