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. It is comparable to an EC50 for agonist drugs. EC50 also represents the plasma concentration required for obtaining 50% of a maximum effect "in vivo".