the ic50 is a measure of how effective a drug is. it indicates how much of a particular drug or other substance is needed to inhibit a given biological process (or component of a process, i.e. an enzyme, cell, cell receptor or microorganism) by half. in other words, it is the half minimal (50%) inhibitory concentration (ic) of a substance (50% ic, or ic50). it is commonly used as a measure of antagonist drug potency in pharmacological research. sometimes, it is also converted to the pic50 scale (-log ic50), in which higher values indicate exponentially greater potency. according to the fda, ic50 represents the concentration of a drug that is required for 50% inhibition "in vitro".