At any particular moment there are over 80,000 clinical trials occurring across the country and around the world. Clinical trials are health-related research studies that involve human beings. These studies can be either "interventional" studies, which focus on a treatment for a disease or condition, or "observational" studies, which focus on observing and studying individual subjects.

Before an interventional research project reaches the human clinical trial stage it has generally been rigorously evaluated in various non-human settings, such as "test tubes" and other laboratory studies, and then possibly animal studies. If a project appears to be useful and beneficial, it must eventually be tested on actual human volunteers to see whether what looked good in the laboratory will actually work as predicted.

The most familiar kind of clinical trial is a study in which the research subjects are assigned by the investigator to a treatment or other intervention, and the results are measured. Many of these trials are "blind." In a blind study, neither the person being studied nor the clinician administering the study know whether the subject is receiving the investigational product. This keeps the results of the study from being accidentaly or unconsciously influenced by either the subject or the administrator.

Choosing whether or not to participate in a clinical trial is an important personal decision. The following information may be helpful when making the decision.

The Kinds of Clinical Trials

Treatment Trials test experimental treatments, new combinations of drugs, or new approaches to surgery or radiation therapy.

Prevention Trials look for better ways to prevent disease in people who have never had the disease or to prevent a disease from returning. These approaches may include medicines, vaccines, vitamins, minerals, or lifestyle changes.

Diagnostic Trials are conducted to find better tests or procedures for diagnosing a particular disease or condition.

Screening Trials test the best way to detect certain diseases or health conditions.

Quality of Life Trials (or Supportive Care trials) explore ways to improve comfort and the quality of life for individuals with a chronic illness.


Clinical trials are conducted in phases. Each phase has a unique purpose and focus:

Phase I Trials: Researchers test an experimental drug or treatment in a small group of 20 to 80 volunteers to evaluate its safety, determine a safe dosage range, and identify side effects.

Phase II Trials: The experimental substance or treatment is studied in a larger group of 100 to 300 individuals to see if it is effective and to further evaluate its safety.

Phase III Trials: The experimental treatment or study drug is given to a large group of 1,000 to 3,000 subjects to further confirm its effectiveness, monitor side effects, compare it to existing commonly used treatments, and collect additional information that will allow the experimental drug or treatment to be used safely.

Phase IV Trials: After the drug has come to market researchers continue to study risks, benefits and best use.

Risks and Benefits of Participating in a Clinical Trial

Clinical trials that are well-designed and well-executed are the best approach for eligible participants to:

Have the opportunity to access to new research treatments before they are widely available;

Obtain expert medical care at leading health care facilities during the trial;

Play an active role in their own health care;

Help others by contributing to medical research.

Risks of clinical trials:

Possible unpleasant, serious or even life-threatening side effects to experimental treatment;

The experimental treatment may not be effective;

Participating may entail more time and attention than not participating, including trips to the study site, more treatments, hospital stays or complex dosage requirements.

What Questions Should You Ask Before Participating in a Clinical Trial?

Anyone considering participation in a clinical trial should know as much as possible before volunteering. Most clinical trials provide short-term treatments related to a designated illness or condition, but do not provide extended or complete primary health care.

What is the purpose of the study?

Who is going to be in the study?

Why do researchers believe the experimental treatment being tested may be effective? Has it been tested before?

What kinds of tests and experimental treatments are involved?

How do the possible risks, side effects, and benefits in the study compare with my current treatment?

How might this trial affect my daily life?

How long will the trial last?

Will hospitalization be required?

Who will pay for the experimental treatment?

Will I be reimbursed for other expenses?

What type of long-term follow up care is part of this study?

How will I know that the experimental treatment is working? Will results of the trials be provided to me?

Who will be in charge of my care?

At any particular moment there are over 80,000 clinical trials occurring across the United States and around the world. If you might have an interest in participating in one, there is an extensive list of current trials in all phases on the ClinicalTrials.gov website with information about each trial's purpose, who may participate, locations, and phone numbers for more details. Some of these trials are small and geographically very limited. Others are very large and geographically diverse. You can search by several criteria, including by illness or condition, by a particular drug intervention in which you might have an interest, by study sponsor, or by location.

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