Clinical Trials: A Guide

Medically Reviewed by Brunilda Nazario, MD on October 24, 2023
5 min read

It’s when a team of scientists and doctors tries a new medical treatment, drug, device, or method on a group of people to test how well it works. The purpose of a clinical trial is to find a new and improved way to treat, prevent, or diagnose different types of illness.

In many cases the trial might be for something that is not yet available to the general population of people with an illness. Special allowances are made so doctors can learn more about how well a new approach works. They test the results against the best available current treatments with the goal of finding something better.

This could be especially useful if you have a serious illness and have run out of effective standard treatments.

Scientists first test these new treatments with laboratory experiments. Next, they try them on laboratory animals. Only when they deem them safe and useful enough in these early stages does a clinical trial start on people -- first in small groups and then in larger ones.

Clinical trials help doctors discover the answers to these questions:

  • Is the treatment safe and effective?
  • How well does the treatment work?
  • Is the treatment potentially better than the treatments we have now?
  • What are the side effects and risks of the treatment?


There are several stages, or “phases,” of a clinical trial. Each new phase builds on information from previous stages.

You might qualify for a certain phase of a trial because of the state of your health or the seriousness of your particular illness. People who take part usually do it in phase III or IV of the trial.


  1. Phase I: Doctors give a new treatment to a small number of people to test safety. The researchers find out the best way to give the new treatment, any possible side effects, and safe dosage.
  2. Phase II: The research team tries to figure out how well the treatment works for a particular illness.
  3. Phase III: The team compares the new treatment with the standard treatment and tries to examine the effects of different dosages and combinations of treatments on different populations (e.g., men, women, young, old, and various ethnic groups).
  4. Phase IV: Here, the treatment is tried on average patients who agree to it. The goal is to look for side effects not found in prior phases and to figure out how well the treatment works over the long term. The FDA allows drugmakers to market the treatment during this phase.



  • You could receive a new treatment before it is widely available to the public.
  • You provide researchers with information that helps them come up with better treatments.
  • Your treatment costs might decrease because the agency that sponsors the study typically pays for tests and doctor visits related to the trial. It’s a good idea to discuss these costs with your medical team before you start.


Almost all treatments carry some risk. The amount will depend on the type of treatment and on your general health.

In general, scientists don’t know as much about how clinical trial treatments affect your body. So there may be more risk of unknown side effects than with already established treatments.


  • You may have more exams and tests than usual. These help the research team follow your progress and collect information.
  • You may need to stop or change your current medications as well as your diet. Always discuss these changes with your medical team first.
  • In some cases you won’t know if you get the new medication or something else that looks just like it (double-blind, placebo-control study). This helps the team test how well the drug works.
  • Your medical team will ask you to sign documents giving them permission to try the new treatment on you (informed consent).


The doctors and nurses doing the trial will explain the treatment to you, including its possible benefits and risks, and then ask you to sign a release form that gives your consent to take part. This is your “informed consent.”

Keep in mind that your signature does not bind you to the study. You can decide to leave the trial at any time and for any reason.

In addition, the informed consent process is ongoing. After you agree to a clinical trial, your medical team should continue to update you with any new information about your treatment that might affect your willingness to stay in the trial.

A trial is typically for a certain condition, and each phase might require a different level of symptoms. If you fit the guidelines for a trial, you may be able to participate. Sometimes you might need certain tests to confirm that you’re a good candidate.

Your personal information is confidential and not attached to your name in the study.

If you are thinking about taking part in a clinical trial, find out as much as possible about the study before you decide to join. Here are some important questions to ask:

  1. What is the purpose of the clinical trial?
  2. What kinds of tests and treatments does the clinical trial involve, and how are these tests given?
  3. What is likely to happen in my case with, or without, this new research treatment? (Are there standard treatments for my case, and how does the study compare with them?)
  4. How could the clinical trial affect my daily life?
  5. What side effects can I expect from the clinical trial? (Note: There can also be side effects from standard treatments and unpleasant effects from the disease itself.)
  6. How long will the clinical trial last?
  7. Will the clinical trial require extra time on my part?
  8. Will I have to be hospitalized? If so, how often and for how long?
  9. If I agree to withdraw from the clinical trial, will my care be affected? Will I need to change doctors?