Participating in Clinical Trials

About Clinical Trials

A Research Study With Human Subjects

A clinical trial is a research study that involves human subjects. The purpose of a clinical trial is to find out if an experimental drug, therapy, medical device, lifestyle change, or test will help treat, find, or prevent a disease. A clinical trial may compare experimental products or tests to those already available or may compare existing treatments with each other in order to determine which one is safer or more effective.

The five main types of clinical trials are treatment, screening, diagnostic, prevention, and supportive care trials.

Treatment Trials

In treatment trials, researchers may

  • gather information about experimental treatments, their risks, and how well they work
  • compare existing therapies to decide which one, or a combination of them, is the best treatment for a disease
  • evaluate treatment methods such as surgical techniques, psychiatric therapy, or radiotherapy.

Scientists usually do years of experiments in the laboratory and in animals before they even consider testing an experimental treatment in people. Most of this early research occurs at universities and medical centers across the country. The National Institutes of Health funds much of this basic research.

Screening Trials

In screening trials, researchers study ways of finding a disease before symptoms occur. 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.

Diagnostic Trials

In diagnostic trials, researchers evaluate 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.

Prevention Trials

In prevention trials, researchers study ways to reduce the risk of getting a disease or a specific medical problem. These trials 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, or vitamins, or getting vaccines will prevent a disease in people who have never had the disease or prevent a disease from returning.

Supportive Care Trials

In supportive care trials, researchers look for ways to make life better for people living with a life threatening disease or chronic health problem. The goal may be to maximize comfort or to manage side effects of treatment. Researchers may study the role of caregivers, support groups, and various types of social interventions. Supportive care interventions are not intended to treat or cure a disease.

Phases of Clinical Trials

Clinical trials of drugs are usually described based on their phase. The U.S. Food and Drug Administration typically requires Phase 1, 2 and 3 trials to be conducted to determine if the drug can be approved for use.

  • A Phase I trial tests an experimental treatment on a small group of often healthy people (20 to 80), to judge its safety and side effects, and to find the correct drug dosage.
  • A Phase II trial uses more people (100 to 300). While the emphasis in Phase 1 is on safety, the emphasis in Phase 2 is on effectiveness. This phase aims to obtain preliminary data on whether the drug works in people who have a certain disease or condition. These trials also continue to study safety, including short-term side effects. This phase can last several years.
  • A Phase III trial gathers more information about safety and effectiveness, studying different populations and different dosages and using the drug in combination with other drugs. The number of subjects usually ranges from several hundred to about 3,000 people. 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.