Ethanol is a small molecule that readily distributes into highly perfused tissues such as the brain. Peak levels of ethanol are attained approximately 30 minutes after ingestion of an alcoholic drink. A single drink of ethanol produces a biphasic effect with a rapid stimulatory phase associated with an increase in blood ethanol concentrations followed by a depressant phase as the blood concentration diminishes. Although the ethanol from a single drink is readily metabolized in two steps involving the enzymes alcohol dehydrogenase and aldehyde dehydrogenase, this process follows zero-order kinetics. Accordingly, there is a decrease in the percentage of ethanol metabolized per given unit of time, as the dose of this agent is increased.