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What is a clinical trial?

A good definition of a clinical trial comes from the National Library of Medicine, which is part of the National Institutes of Health. A clinical trial is a research study in human volunteers to answer specific health questions. Carefully conducted clinical trials are the fastest and safest ways to find treatments that work in people and ways to improve health.

To learn more about clinical trials, watch the below videos or click the boxes below.

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Find a clinical trial

ClinicalTrials.gov is a registry and results database of publicly and privately supported clinical studies of human participants conducted around the world. To find a clinical trial at UCLA CTSI institutions (UCLA-Westwood, Cedars-Sinai Medical Center, Los Angeles Biomedical Institute at Harbor-UCLA Medical Center, Charles R. Drew University of Medicine and Science) or other locations, go to www.clinicaltrials.gov.

Find a UC-wide clinical trial

UC-wide Clinical Trials gives you information about the trials going on at the UC medical campuses (UC Davis, UC Irvine, UC Los Angeles, UC San Diego, and UC San Francisco). This site includes data from our university, ClinicalTrials.gov (details), and other sources., go to http://clinicaltrials.ucbraid.org


Are there different kinds of clinical trials?

The National Library of Medicine explains that clinical trials fall into two general categories. Interventional trials determine whether experimental treatments or new ways of using approved therapies are safe and effective under controlled conditions. For example, doctors may give an experimental drug to breast cancer patients to see whether their health improves. Observational trials study health issues in large groups of people in natural settings. For example, an observational trial might follow a group of older adults to learn about the effect of different lifestyles on heart disease.

How do I register for a clinical trial?

To search for a clinical trial at UCLA CTSI institutions (UCLA-Westwood, Cedars-Sinai Medical Center, Los Angeles Biomedical Institute at Harbor-UCLA Medical Center, Charles R. Drew University of Medicine and Science) go to www.clinicaltrials.gov.

What sorts of things are tested in clinical trials?

The technologies and measurements tested in clinical trials fall into five main categories.

  • Treatment trials test the safety and efficacy of experimental drugs, devices, and treatment methods, such as surgical techniques, psychiatric therapy or radiotherapy, in people with specific diseases or health conditions.
  • Prevention trials study ways to reduce the risk of getting a disease or specific medical problem. Examples include studies that look at the effects of vaccines, exercise or sleep.
  • Diagnostic trials test the accuracy of experimental technologies designed to identify a specific disease or health condition in its early stages.
  • Screening trials test the accuracy of experimental technologies to detect disease before symptoms occur.
  • Supportive care trials test ways to improve the well-being people with people with life-threatening disease or chronic health conditions. Supportive care interventions may be aimed at increasing comfort or reducing side effects. They are not intended to treat or cure disease.

What are the phases of a clinical trial?

The Food and Drug Administration (FDA) typically requires that experimental drugs be tested in three phases in stepwise fashion to determine if the experimental drugs are safe and effective.

  • Phase I clinical trials test the safety and determine the side effects of experimental drugs in small numbers of healthy people. Phase I studies also help find the correct dosage.
  • Phase II clinical trials test the effectiveness of experimental drugs in people with specific diseases or health conditions. These trials also collect information about safety and side effects.
  • Phase III clinical trials gather information about the safety and effectiveness of experimental drugs in different populations and at different dosages. If the results are positive, the FDA may approve the drug for sale.

The FDA may also require Phase IV studies. A phase IV study monitors the long-term safety and effectiveness of a drug after it is on the market.

What protections exist for people who participate in clinical trials?

Every clinical trial in the United States must be approved and monitored by an Institutional Review Board (IRB) to make sure the risks are as low as possible and are worth the potential benefits of the experimental therapy. The IRB is charged wit\ h ensuring a study is ethical and that the participants are not likely to be harmed.

The IRB-a committed of physicians, statisticians, patient advocates and others-can stop a study if the experimental treatment causes unexpected harm. The IRB can also stop a study if there is clear evidence that the experimental treatment is effe\ ctive.

Follow this link for information about IRBs at UCLA.

What are the benefits and risks of participating in a clinical trial?

The National Institutes of Health provides the following summary of the benefits and risks of clinical trial participation.


  • Your participation may help others get a better treatment for their disease in the future and allow researchers to learn more about how diseases can be prevented, identified, or managed.
  • If the treatment being studied is more effective than the standard treatment, you may be among the first to benefit.
  • Researchers, doctors, and other health care professionals may check your physical condition frequently, giving you regular, careful medical attention, because they need data to make comparisons in a trial.
  • It may be a way to get an experimental treatment for a life threatening illness that is not available to people outside of a clinical trial.


  • You may experience unpleasant, serious, or even life-threatening side effects.
  • You may not get the experimental treatment, but a standard treatment or a placebo instead.
  • The experimental may not work or it may not be better or even as good as the standard treatment for your condition.
  • You may be required to make more visits to the doctor than if you were receiving standard treatment. You may have extra expenses related to these extra visits, such as travel and childcare costs.
  • You may need extra tests. Some of the tests could be uncomfortable or time consuming.
  • Even if a new treatment has benefits in some patients, it may not work for you.
  • Health insurance may not cover all patient care costs in a trial.

Remember, it is always good to ask questions so you can understand the benefits and risks of entering a specific clinical trial.

Questions to ask before participating in a clinical trial

The National Cancer Institute, which is part of NIH, recommends asking your doctor these questions before entering a clinical trial.

About the trial:

  • What is the purpose of the trial?
  • Why do the researchers believe that the treatment being studied may be better than the one being used now? Why may it not be better?
  • How long will I be in the trial?
  • What kinds of tests and treatments are involved?
  • How will the doctor know if the treatment is working?
  • How will I be told about the trial's results?
  • How long do I have to make up my mind about joining this trial?
  • Who can I speak with about questions I have during and after the trial?
  • Who will be in charge of my care?
  • Is there someone I can talk to who has been in the trial?

Risks and benefits:

  • What are the possible side effects or risks of the new treatment?
  • What are the possible benefits?
  • How do the possible risks and benefits of this trial compare to those of the standard treatment?

Patient rights:

  • How will my health information be kept private?
  • What happens if I decide to leave the trial?


  • Will I have to pay for any of the treatments or tests?
  • What costs will my health insurance cover?
  • Who pays if I'm injured in the trial?
  • Who can help answer any questions from my insurance company?

Daily life:

  • How could the trial affect my daily life?
  • How often will I have to come to the hospital or clinic?
  • Will I have to stay in the hospital during the clinical trial? If so, how often and for how long?
  • Will I have to travel long distances?
  • Will I have check-ups after the trial?

Comparing choices:

  • What are my other treatment choices, including standard treatments?
  • How does the treatment I would receive in this trial compare with the other treatment choices?
  • What will happen to my cancer without treatment?

Where can I find more information about clinical trials?

NIH Senior Health has clinical trial information, a catalog of short videos, FAQs and other useful information.

Medline, a service of the National Library of Medicine, has interactive tutorials, and links to information about specific health conditions. An English-language tutorial can be found here; a Spa\ nish-language tutorial can be found here.

The National Cancer Institute provides information on participating and paying for care in clinical trials.

The Food and Drug Administration has FAQs about clinical trials in English and Spanish.

Research terms glossary

Just like any field of work, medical science comes with a host of words and phrases that can be difficult to understand in the context of a clinical trial. Sifting through the information and explanations can be time consuming and occasionally difficult. ClinicalTrials.gov has created a glossary of frequently used research terms. For volunteers interested in participating in a cancer clinical trial, UCLA's Jonsson Comprehensive Cancer Center has created a more specific glossary of terms often use\ d with cancer research.