In the present health care scenario most of the health care personnel assume that the drug-drug interactions are the only interactions with clinical importance and are basically unaware of the fact that there are more potentially harmful drug interactions than drug-drug interactions. The knowledge of drug interactions that are likely to occur in the case of cigarette smoking and alcohol ingestion can empower a physician to avoid drug interactions that lead to deleterious outcomes. Both smoking and alcoholism can have several stimulatory and inhibitory effects on the several pharmacokinetic and pharmacodynamic properties of a drug