What is a "phase" in a clinical trial, and which one am I in?

What is a "phase" in a clinical trial, and which one am I in?

Institutional Review Board (IRB) FAQs What is a "phase" in a clinical trial, and which one am I in?

What is a "phase" in a clinical trial, and which one am I in?

​Phase 1 trials include the initial introduction of an investigational new drug into humans. These studies are typically conducted with healthy volunteers; sometimes, where the drug is intended for use in patients with a particular disease, however, such patients may participate as subjects. Phase 1 trials are designed to determine the metabolic and pharmacological actions of the drug in humans, the side effects associated with increasing doses (to establish a safe dose range), and, if possible, to gain early evidence of effectiveness; they are typically closely monitored. The ultimate goal of Phase 1 trials is to obtain sufficient information about the drug's pharmacokinetics and pharmacological effects to permit the design of well-controlled, sufficiently valid Phase 2 studies. Other examples of Phase 1 studies include studies of drug metabolism, structure-activity relationships, and mechanisms of actions in humans, as well as studies in which investigational drugs are used as research tools to explore biological phenomena or disease processes. The total number of participants involved in Phase 1 investigations is generally in the range of 20-80.

PHASE 2 DRUG TRIAL Phase 2 trials include controlled clinical studies conducted to evaluate the drug's effectiveness for a particular indication in patients with the disease or condition under study, and to determine the common short-term side effects and risks associated with the drug. These studies are typically well-controlled, closely monitored, and conducted with a relatively small number of patients, usually involving no more than several hundred participants.

PHASE 3 DRUG TRIAL Phase 3 trials involve the administration of a new drug to a larger number of patients in different clinical settings to determine its safety, efficacy, and appropriate dosage. They are performed after preliminary evidence of effectiveness has been obtained, and are intended to gather necessary additional information about effectiveness and safety for evaluating the overall benefit-risk relationship of the drug, and to provide an adequate basis for physician labeling. In Phase 3 studies, the drug is used the way it would be administered when marketed. When these studies are completed and the sponsor believes that the drug is safe and effective under specific conditions, the sponsor applies to the FDA for approval to market the drug. Phase 3 trials usually involve several hundred to several thousand patient-subjects.

PHASE 4 DRUG TRIAL Concurrent with marketing approval, FDA may seek agreement from the sponsor to conduct certain postmarketing (Phase 4) studies to delineate additional information about the drug's risks, benefits, and optimal use. These studies could include, but would not be limited to, studying different doses or schedules of administration than were used in Phase 2 studies, use of the drug in other patient populations or other stages of the disease, or use of the drug over a longer period of time [21 CFR §312.85].

Related FAQs
  • What is a human subject?

    ​The definition of a "human subject" is contained in POL001: UAB Policy on the Protection of Human Subjects in Research.

    OHRP Human Subject Regulations Decision Charts.  Charts from the Office for Human Research Protections to determine whether research uses "human subjects"
  • What does minimal risk mean?

    ​The Common Rule defines minimum risk—for non-prisoners—as risk in which "the probability and magnitude of harm or discomfort anticipated in the research are not greater in and of themselves than those ordinarily encountered in daily life or during the performance of routine physical or psychological examinations or tests" (45 CFR 46.102).

    For prisoners, minimal risk is defined as risk in which "the probability and magnitude of physical or psychological harm that is normally encountered in the daily lives, or in the routine medical, dental, or psychological examination of healthy persons" (45 CFR 46.303).

  • For purposes of human subjects protection, how is research defined?

    ​Research is defined by the regulations as "a systematic investigation, including research development, testing and evaluation, designed to develop or contribute to generalizable knowledge." If you are conducting a study that you expect to publish or report in a public forum, you should consider it research and subject to IRB jurisdiction if it involves human subjects. If you are collecting data only for internal use, for example to improve customer service in your department, you are not doing research.


  • How do we assure someone is the participant’s “legally authorized representative?"

    ​Parents are legally authorized representatives for their children. If someone other than the parents asserts that he or she is the legally authorized representative, you should obtain a copy of the court documents naming the individual as guardian or conservator. 

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