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[[File:IC50 determination illustration.png|thumb|Graphical representation of the IC50 determination of the inhibition of an enzyme's activity by a small molecule ("drug"). Four different concentrations of the small molecule (ranging from 30 to 300 μM) were tested.]]'''Half maximal inhibitory concentration (IC<sub>50</sub>)''' is a measure of the potency of a substance in inhibiting a specific biological or biochemical function. IC<sub>50</sub> is a quantitative measure that indicates how much of a particular inhibitory substance (e.g. drug) is needed to inhibit, ''in vitro'', a given biological process or biological component by 50%. The biological component could be an enzyme, cell, cell receptor or microorganism. IC<sub>50</sub> values are typically expressed as molar concentration.

IC<sub>50</sub> is commonly used as a measure of antagonist drug potency in pharmacological research. IC<sub>50</sub> is comparable to other measures of potency, such as [[EC50|EC<sub>50</sub>]] for excitatory drugs. EC<sub>50</sub> represents the dose or plasma concentration required for obtaining 50% of a maximum effect ''in vivo''.

IC<sub>50</sub> can be determined with functional assays or with competition binding assays.

Sometimes, IC<sub>50</sub> values are converted to the '''pIC<sub>50</sub>''' scale.
:<math chem="">\ce{pIC_{50}} = -\log_{10} \ce{(IC_{50})}</math>
Due to the minus sign, higher values of pIC<sub>50</sub> indicate exponentially more potent inhibitors. pIC<sub>50</sub> is usually given in terms of molar concentration (mol/L, or M), thus requiring IC<sub>50</sub> in units of M.{{pmid|6882621}}

== See Also ==
* [[EC50|EC<sub>50</sub>]]
* {{SeeWikipedia|IC50}}

== References ==
<references />
[[Category:Pharmacokinetics]]