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About Clinical Trials

The National Institutes of Health (NIH) identifies the following types of clinical trials:

  • Treatment: Test new treatments or devices, new combination of drugs, or new approaches to surgery or radiation therapy. Treatment trials are often categorized by phases. (See Phases of clinical trials.)
  • Natural History: Provides information about how health and disease progress over time.
  • Prevention: Evaluate the effectiveness of ways to reduce the risk of developing a disease or preventing a disease from returning.
  • Diagnostic: Develop better tests or procedures to identify/diagnose a particular disease or condition more accurately.
  • Screening: Assess new ways of detecting disease earlier in healthy people.
  • Quality of life (or supportive care): Evaluate measures to improve comfort of and quality of life for people with chronic illnesses through better therapies or psychosocial interventions.

Trials involving orphan or rare diseases may be awarded a special status that grants permission to run trials with much lower numbers of participants. Orphan designations include:

  • Rare disease -- defined as fewer than 200,000 people in the United States having the disease, with some diseases considered to be “ultra orphan.”
  • Awarded by FDA to drugs developed explicitly for serious and life-threatening rare diseases, for which there is no treatment.
  • Awarded to drugs that have shown promise of being effective to treat these diseases.
  • Incentives awarded to help get the drug through the FDA approval process.
  • Additional incentives gained once drug has FDA approval, again to encourage companies to help develop drugs for rare diseases.

Each clinical trial phase has a different purpose and helps answer different questions.

  • Phase I trials: Researchers test an experimental drug or treatment in a small group of people (20–80) for the first time, often using healthy volunteers to test drug metabolism, safety, and dose ranges. The purpose is to evaluate its safety and identify side effects.
  • Phase II trials: The experimental drug or treatment is administered to a larger group of people (100–300) to determine its effectiveness, optimal therapeutic dose, and to further evaluate its safety. This phase may be blinded (unknown if patient receives the study drug) or open label studies (known if patient receives study drug) in the target population. The target population encompasses the group for which the drug is ultimately intended. Any drug metabolism, safety, or dosing difference between the Phase I healthy individuals and the Phase II target population is also evaluated. Hints of efficacy may be obtained as well.
  • Phase III trials: The experimental drug or treatment is administered to large groups of people (1,000–3,000*) to confirm its effectiveness, monitor side effects, compare it with standard or equivalent treatments, and collect information that will allow the experimental drug or treatment to be used safely. Phase II studies are randomized, double-blind, placebo-controlled in target population for hard data on safety and efficacy. Phase II studies are needed to ensure that bias does not affect study results.
  • Phase IV trials: After a drug is approved by the FDA and made available to the public, researchers track its safety, seeking more information about a drug or side effects.