Title: phase II clinical studies
Long Title: IUPAC Gold Book - phase II clinical studies
DOI: 10.1351/goldbook.12709
Status: current

Definition
Controlled clinical studies conducted in a limited number of individuals to obtain some preliminary data on the effectiveness of an investigational new drug for a particular indication or indications in patients with the disease or condition.

Note
Phase II clinical trials have two subclasses, IIa and IIb. Phase IIa trials are essentially pilot clinical trials designed to evaluate efficacy (and safety) in selected populations of patients with the disease or condition to be treated, diagnosed, or prevented. Phase IIb trials extend those of Phase IIa to well-controlled trials that evaluate the same parameters in similar patient populations.

Related Terms
- investigational new drug: https://goldbook.iupac.org/terms/view/12673
- phase 0: https://goldbook.iupac.org/terms/view/12707
- phase I: https://goldbook.iupac.org/terms/view/12708
- phase III: https://goldbook.iupac.org/terms/view/12710
- phase IV: https://goldbook.iupac.org/terms/view/12711

Source
- PAC, 2013, 85, 1725. 'Glossary of terms used in medicinal chemistry. Part II (IUPAC Recommendations 2013)' on page 1746 (https://doi.org/10.1351/PAC-REC-12-11-23)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/12709/html
- json: https://goldbook.iupac.org/terms/view/12709/json
- xml: https://goldbook.iupac.org/terms/view/12709/xml

Citation: Citation: 'phase II clinical studies' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.12709
License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.
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Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.
Accessed: 2026-06-27T11:01:58+00:00