The concepts of EC50 and IC50, albeit similar, are not quite identical. While EC50 measures the concentration of a drug inducing its half-maximal effective response, IC50 represents the concentration of an inhibitor at which 50% of inhibition in its activity is achieved. A good way to remember the difference is using the acronym ‘I’ in IC50, which stands for inhibition, unlike ‘E’ in EC50, which refers to effective.