Title: inhibitory concentration at 50%
Long Title: IUPAC Gold Book - inhibitory concentration at 50%
DOI: 10.1351/goldbook.12669
Status: current

Definition
The concentration of an enzyme inhibitor or receptor antagonist that reduces the enzyme activity or agonist response by \(\pu{50\%}\).

Note
\(\pu{IC_{50}}\) values are influenced by experimental conditions (e.g., substrate or agonist concentration, which should be specified).

Related Term
- inhibition constant: https://goldbook.iupac.org//terms/view/12670

Source
- PAC, 2013, 85, 1725. 'Glossary of terms used in medicinal chemistry. Part II (IUPAC Recommendations 2013)' on page 1737 (https://doi.org/10.1351/PAC-REC-12-11-23)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/12669/html
- json: https://goldbook.iupac.org/terms/view/12669/json
- xml: https://goldbook.iupac.org/terms/view/12669/xml

Citation: Citation: 'inhibitory concentration at 50%' 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.12669
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: 2026-07-16T01:20:20+00:00