A clinical trial is a research study in which volunteers receive investigational treatments under the supervision of a physician and other research professionals. These treatments are developed by pharmaceutical and biotechnology companies who select qualified physicians, also known as investigators, to conduct clinical trials to determine the benefits of investigational drugs.

Clinical trials are usually conducted in three pre-marketing phases (I, II, III) followed by a post-marketing phase (IV). Only a small number of people participate in phase I trials while the later phases involve a larger number of volunteers.

Phase I studies assess the safety of a drug or device. This initial phase of testing, which can take several months to complete, usually includes a small number of healthy volunteers (20 to 100), who are generally compensated for participating in the study. The study is designed to determine the effects of the drug or device on humans, including how it is absorbed, metabolized, and excreted. This phase also investigates the side effects that occur as dosage levels are increased. About 70% of experimental drugs pass this phase of testing.

Phase II studies test the efficacy of a drug or device. This second phase of testing can last from several months to two years, and involves up to several hundred patients. Most phase II studies are randomized trials where one group of patients receives the experimental drug, while a second "control" group receives a standard treatment or placebo.

Often these studies are "blinded" which means that neither the patients nor the researchers know who has received the experimental drug. Blinding allows investigators to provide the pharmaceutical company and the FDA with comparative information about the relative safety and effectiveness of the new drug. About one-third of experimental drugs successfully complete both Phase I and Phase II studies.

Phase III studies involve randomized and blind testing in several hundred to several thousand patients. This large-scale testing, which can last several years, provides the pharmaceutical company and the FDA with a more thorough understanding of the effectiveness of the drug or device, the benefits and the range of possible adverse reactions. Seventy to ninety percent of drugs that enter Phase III studies successfully complete this phase of testing. Once Phase III is complete, a pharmaceutical company can request FDA approval for marketing the drug.

Phase IV studies, often called Post Marketing Surveillance Trials, are conducted after a drug or device has been approved for consumer sale. Pharmaceutical companies have several objectives at this stage: (1) to compare a drug with other drugs already in the market; (2) to monitor a drug's long-term effectiveness and impact on a patient's quality of life; and (3) to determine the cost-effectiveness of a drug therapy relative to other traditional and new therapies. Phase IV studies can result in a drug or device being taken off the market or restrictions of use could be placed on the product depending on the findings in the study.

Funding for clinical research comes from both the federal government (through the National Institutes of Health) and private industry (pharmaceutical and biotech companies). The sponsor of the research hires physicians, who may work in a wide variety of health-care settings, to conduct the clinical trial.

Physicians are typically compensated on a per-patient basis. The medical care is often provided at no cost to the patient. Patients may also be compensated a small fee to participate in a clinical trial.

People participate in clinical research for a variety of reasons. People who volunteer for phase II and phase III trials can gain access to promising drugs long before these compounds are approved for the marketplace. They typically will get excellent care from the physicians during the course of the study. This care also may be provided at no cost.

The patient's rights and safety are protected in two important ways. First, any physician awarded a research grant by a pharmaceutical company or the NIH must obtain approval to conduct the study from an Institutional Review Board. The review board, which is usually composed of physicians and lay people, is charged with examining the study's protocol to ensure that the patient's rights are protected, and that the study does not present an undue or unnecessary risk to the patient.

Second, anyone participating in a clinical trial in the United States is required to sign an "informed consent" form. This form details the nature of the study, the risks involved, and what may happen to a patient in the study. The informed consent tells patients that they have a right to leave the study at any time.

Patients considering participating in clinical research should talk about it with their physicians and medical caregivers. They should also seek to understand the credentials and experience of the individuals and the facility involved in conducting the study.

The National Institutes of Allergy and Infectious Disease at the National Institutes of Health provides detailed information for patients considering participating in a clinical trial on their web site in the section entitled "The Clinical Trial Process."

How long will the trial last? What treatments will be used? What is the main purpose of the trial? How will patient safety be monitored? What are the risks? What are the possible benefits? Are there alternate treatments already available? What happens if I am harmed by the trial? Can I opt to remain on this treatment even after the study ends?