Drug Interactions and Alcohol - Encyclopedia of Drugs, Alcohol & Addictive Behavior (Vol. 2. 3rd ed.)The term alcohol-drug interaction refers to the possibility that alcohol may alter the intensity of the pharmacological effect of a drug, so that the overall actions of the combination of alcohol plus drug are additive, potentiated, or antagonistic. Such interactions can be divided into two broad categories—pharmacokinetic and pharmacodynamic. Pharmacokinetics are concerned with the extent and rate of absorption of the drugs, their distribution within the body, binding to tissues, biotransformation (metabolism), and excretion. Pharmacokinetic interactions refer to the ability of alcohol to alter the plasma and tissue concentration of the drug and/or the drug metabolites, such that the effective concentration of the drug at its target site of action is significantly decreased or increased. Pharmacodynamics are concerned with the biochemical and physiological effects of drugs and their mechanisms of action. Pharmacodynamic interactions refer to the combined actions of alcohol and the drug at the target site of action, for example, binding to enzyme, receptor, carrier, or macromolecules. Pharmacodynamic interactions may occur with or without a pharmacokinetic component. For many drugs acting on the central nervous system that exhibit cross-tolerance (a similar tolerance level) with alcohol, pharmacodynamic interactions with alcohol are especially important.