The effects of chronic use of alcohol on drug metabolism are dependent on many variables, which determine the final outcome. The degree of liver injury, the inducing effect of long-term alcohol use and also macromorphological changes connected with advanced stages of alcohol-induced liver injury are of importance. Alcohol may also affect the toxification of foreign chemicals by the liver, thus rendering an individual more susceptible to chemical-induced toxic reactions. It is not possible to predict drug-metabolizing capacity of an alcoholic from clinical history, liver histology or serum biochemistry, although generally correlations among these parameters and hepatic drug-metabolizing enzymes are statistically significant. Consequently, direct assays for drug metabolism, e.g. the elimination of a test drug (e.g. antipyrine) or the drug under study itself, or enzyme measurements in biopsy samples, are needed if one wants to pursue "tailor-made" drug therapy for an alcoholic.