A clinical trial is a study that uses human subjects to find out if a drug, therapy, medical device, or test will find, prevent, or help treat a disease.

Researchers also use trials to find out if experimental treatments or tests are safer or more effective than what is already available.

There are several different types of clinical trials.

• Treatment trials
• Screening trials
• diagnostic trials
• Prevention trials
• Quality of life trials

The most common trial is the treatment trial. In treatment trials, researchers gather information about how well an experimental drug, medical device, or medical procedure works. Sometimes they compare different treatments to see which one works best.

In a screening trial, researchers learn about new ways of finding a disease before symptoms show up. These methods, often called screening tests, can include

• imaging tests that produce pictures of what is inside the body
• laboratory tests that check samples of blood, urine, or other body tissues
• genetic tests that look for genes linked to some types of disease.

Prevention trials study ways to reduce the risk of getting a disease. These trials attempt to find out if

• lifestyle changes, such as exercising more, getting more sleep, keeping mentally active, or eating nutritious foods, can prevent a problem
• taking certain medicines, vitamins, or getting vaccines will prevent diseases.

Diagnostic trials find new tests that could identify a disease in its early stages. Usually, trial participants must show signs of the disease or condition before they can join this type of trial.

Quality of life trials find ways to make life better for people living with a life threatening disease or chronic health problem. For example, they may study the role of caregivers, support groups, and various types of social interventions.

Here are ways you may benefit from taking part in a clinical trial.

• You may get an experimental treatment for a life threatening illness before it is approved and available to the public.
• You may get more health checkups because the researchers need data to make comparisons in the trial.
• You may help others get a better treatment for their disease in the future.

Here are some possible risks of taking part in a clinical trial.

• You may experience serious side effects.
• You may get the standard treatment or placebo instead of the experimental treatment.
• The experimental treatment may not be better or even as good as the standard treatment for your condition.
• Even if a new procedure works for other people, it may not work for you.

Since older adults take more medicine than any other group, it is important to find out how they might respond to new medications, especially those that target diseases and conditions of aging.

Older adults should take part in clinical trials because the trial results can lead to new treatments for many diseases and conditions that affect older adults such as Alzheimer's disease, heart disease, various types of cancers, stroke, and diabetes.

Researchers also need to know how potential new drugs, therapies, medical devices or tests may work in older people. As people age, their bodies absorb drugs differently. They may need to take different dosages of drugs than younger people, and they may have different side effects.

For more on older adults and medicines go to Taking Medicines at http://nihseniorhealth.gov/takingmedicines/toc.html

Clinical trials need older participants so that researchers can better learn how potential new drugs, therapies, medical devices, or tests work in older people.

When older adults participate in greater numbers, researchers will have better information about ways to diagnose, prevent, treat, and cure diseases and conditions of aging.

Researchers may not include older people in trials because of worries that the treatment won't work as well for them, or there may be severe side effects that could have an effect on their quality of life.

Older adults may not join trials because of a lack of support by friends and family, the costs of care, or difficulty getting to health care centers where many trials take place.

Also, many times older people may have several health problems at the same time such as diabetes, high blood pressure or heart disease which might affect trial results.

A clinical trial usually includes three phases. In some cases, four phases may be required.

A Phase I trial tests an experimental treatment on a small group of often healthy people, to judge its safety and side effects, and to find the correct drug dosage.

A Phase II trial is similar to a Phase I trial but uses more people to find out if the experimental treatment is effective and safe. This phase can last several years.

A Phase III trial is a large study using several hundred or more participants. This phase compares the experimental drug or procedure to a placebo or standard treatment, to make sure it is safe and works well. Some side effects that didn't show up in Phase II may show up in a Phase III trial because many more people are tested.

If the U.S. Food and Drug Administration agrees that the trial results are positive, they will approve the experimental drug or device.

A Phase IV trial for drugs or devices takes place after the U.S. Food and Drug Administration approves their use. A device or drug's effectiveness and safety are monitored in large, diverse populations. Sometimes the side effects of a drug may not become clear until more people have taken it over a longer period of time.

Federal agencies like the National Institutes of Health, drug companies, universities, disease support groups, foundations, and other groups fund clinical trial research.

Clinical trials take place in doctors' offices, community medical centers, university clinics or medical centers, hospitals and clinics, and veterans or military hospitals. They take place in the USA and other countries. One trial may be held in many locations or just one place.

Your healthcare provider may know about trials that you can join. Newspapers in large cities and disease support groups often have lists of trials. The National Institutes of Health has a database called ClinicalTrials.gov that you or your doctor can search at http://clinicaltrials.gov.

Yes. Healthy people of all ages are needed, especially for prevention or screening trials.

A protocol is the detailed study plan that will be followed to answer specific research questions and protect the trial participants. It describes

• what type of people are needed in the trial
• the schedule of tests, procedures, drugs, and dosages
• how long the study will last.

Inclusion and exclusion criteria are the set of qualifications listed in the protocol that allow or prevent someone from taking part in a clinical trial. These may include age, gender, the type and stage of a disease, previous treatments, and other medical conditions.

A standard treatment is a therapy that is effective for a specific disease or condition, currently in wide use, and usually has been approved by the U.S. Food and Drug Administration.

A placebo, sometimes called a sugar pill, is a substance that looks like the experimental drug but has no active ingredients.

Researchers compare experimental drugs with placebos to measure the effectiveness of a treatment.

The control group is the group of trial participants that do not get the experimental drug or procedure. They get a standard treatment for the disease or condition, a placebo, or no treatment at all.

No. Participants in a large drug trial are randomly assigned to an experimental treatment group or a control group. Participants are not supposed to know what they are getting because that might affect the results. In a "double-blind" trial, neither the participants nor the researchers know who is getting the experimental therapy.

Side effects or adverse reactions are unwanted or unexpected negative effects, such as a headache or skin irritation, caused by taking a drug or treatment procedures. Adverse reactions are more serious side effects that can even be life-threatening. [Editor's note: this definition of adverse reactions is wrong. Adverse reactions are side effects that can reasonably be related to the use of the study drug. "Serious adverse events" is the more correct term for side effects that result in hospitalization, may be life-threatening, or result in death, disability, or congenital anomalies.]

Informed consent is an ongoing process that helps you decide whether to enroll in a trial after you have been told all about the study. The informed consent document is an agreement to take part in a trial.

During the first meeting, and in follow-up meetings, the research team will tell you about

• tests or treatments that you may get if you are assigned to the treatment group
• possible risks and benefits of these tests or treatments
• standard tests and treatments available now
• what you need to do, such as take medications at a certain time.

Once you agree to participate in the trial, you must sign the informed consent document. However, it is not a contract. You can leave the trial at any time for any reason.

If you have concerns about your safety being protected by someone other than the research team, there are outside organizations that protect trial participants. They will stop a trial if they find that the experimental treatment is harming the participants or not having any effect. These organizations include Institutional Review Boards and Data and Safety Monitoring Committees.

Before starting a trial, researchers must get permission from their organization's Institutional Review Board or IRB. IRB members are independent of the study and do not have an interest in how it turns out. The IRB reviews the trial's protocol, or study plan, to look for possible benefits and risks to human subjects.

Data and Safety Monitoring Committees are independent of the study and look at data collected during studies comparing different drugs. They pay special attention to treatment trials for life threatening diseases. If a committee finds the experimental treatment is harming participants or is not working, it will stop the study.

Yes. You may leave a clinical trial at any time, for any reason. Signing an informed consent document is not like signing a contract.

Your health insurance coverage may not include all the patient care costs related to a clinical trial. You may have to pay for care which is not a part of the routine tests or procedures that your insurance normally covers.

Medicare does cover some trial costs. You may get some payment from the researchers to cover expenses like transportation. Each trial is different, so be sure to ask the trial administrator about costs.

Clinical trials can be stopped any time in any phase of testing for several reasons.

• Early results may show that the experimental treatment works much better than the others. In these cases, researchers would offer the experimental treatment to the control group.
• The study may find no difference between the control group and treatment group, so further testing is useless.
• The IRB or the Data and Safety Monitoring Committee may find a problem with the way the researchers are running the trial.
• There may be too many dangerous side effects.