An inhibitor can be a drug or chemical that binds typically to some manner of enzyme and generally acts to decrease or diminish the activity of the enzyme. Such inhibitors can elicit their actions in a variety of ways, including binding to and physically blocking the active site of an enzyme that usually receives and binds a natural substrate. Depending on the specific inhibitor it may inhibit the activity of certain enzymes strongly, moderately, or only weakly. Moreover, inhibitors may bind enzymes reversibly or irreversibly.