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Phase 2 trial

A Phase 2 trial is a stage of human testing designed to assess how well a drug works, while continuing the Phase I safety assessments in a larger group of volunteers and patients[1]. Once a dose or range of doses has been determined, the next goal is to evaluate whether the drug has any biological activity or effect[1].

Phase II trials are performed on larger groups than Phase I, typically 50–300 individuals[1]. Genetic testing is common, particularly when there is evidence of variation in metabolic rate[1].

Some Phase II trials are designed as case series, demonstrating a drug's safety and activity in a selected group of participants[2]. Others are designed as randomized controlled trials, where some patients receive the drug or device and others receive a placebo or standard treatment[2]. Randomized Phase II trials have far fewer patients than randomized Phase III trials[2].

In cancer research, the first stage of a Phase II study tries to rule out drugs that have no or little biologic activity[1]. A typical cancer Phase II study might include fewer than 30 people to estimate the response rate[1]. The design of a trial may be altered while it runs, usually during Phase II or III, to accommodate interim results, adjust the statistical analysis, or end an unsuccessful design early, which is called an adaptive design[3]. Phase II studies may cost as little as $7 million for cardiovascular projects and as much as $20 million for hematology trials[4].

Why it matters to investors

When the development of a new drug fails, this usually happens during Phase II trials, when the drug is discovered not to work as planned or to have toxic effects[5].

On this site

Related: Phase 1 trial, Phase 3 trial, Randomized controlled trial

Sources

  1. DeMets D, Friedman L, Furberg C (2010). Fundamentals of Clinical Trials (4th ed.). Springer. ISBN 978-1-4419-1585-6 . (via Wikipedia: Phases of clinical research)
  2. "The drug development process" . US Food and Drug Administration. 4 January 2018. Archived from the original on 26 August 2019 . Retrieved 17 August 2020 . web.archive.org (via Wikipedia: Phases of clinical research)
  3. Van Norman GA (June 2019). "Phase II trials in drug development and adaptive trial design" . JACC. Basic to Translational Science . 4 (3): 428– 437. doi : 10.1016/j.jacbts.2019.02.005 . PMC 6609997 . PMID 31312766 . ncbi.nlm.nih.gov; "Adaptive Designs for Clinical Trials of Drugs and Biologics: Guidance for Industry" (PDF) . U.S. Food and Drug Administration. 1 November 2019 . Retrieved 3 April 2020 . [ dead link ] fda.gov; Pallmann P, Bedding AW, Choodari-Oskooei B, Dimairo M, Flight L, Hampson LV, et al. (February 2018). "Adaptive designs in clinical trials: why use them, and how to run and report them" . BMC Medicine . 16 (1) 29. doi : 10.1186/s12916-018-1017-7 . PMC 5830330 . PMID 29490655 . {{ cite journal }} : CS1 maint: overridden setting ( link ) ncbi.nlm.nih.gov (via Wikipedia: Phases of clinical research)
  4. Sertkaya A, Wong HH, Jessup A, Beleche T (April 2016). "Key cost drivers of pharmaceutical clinical trials in the United States" . Clinical Trials . 13 (2): 117– 26. doi : 10.1177/1740774515625964 . PMID 26908540 . S2CID 24308679 . doi.org (via Wikipedia: Phases of clinical research)
  5. Sun D, Gao W, Hu H, Zhou S (July 2022). "Why 90% of clinical drug development fails and how to improve it?" . Acta Pharmaceutica Sinica. B . 12 (7): 3049– 3062. doi : 10.1016/j.apsb.2022.02.002 . PMC 9293739 . PMID 35865092 . ncbi.nlm.nih.gov (via Wikipedia: Phases of clinical research)

Checked 8 October 2026. How we check sources