12709 IUPAC Gold Book - phase II clinical studies 10.1351/goldbook.12709 12709 current 1 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. 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. 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 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) https://goldbook.iupac.org/terms/view/12709/html https://goldbook.iupac.org/terms/view/12709/json https://goldbook.iupac.org/terms/view/12709/plain 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 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. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . 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. 2026-06-27T11:00:06+00:00