Background and aims This article reviews the published literature on the mechanisms by which drugs alter nutrient intake and the interactions between drugs and nutrients. We aimed to examine evidence of nutrient deficiencies caused by drug therapy, to indicate groups of ‘at-risk’ patients and suggestions made for practical methods of detection and intervention. Methods Information was retrieved from a MEDLINE search of English language literature from 1963 to January 1999. Search terms included nutrient, deficiencies and interactions. Additional references were obtained from cross-referencing related review articles and from pharmacology textbooks relating to interactions and side-effects of drugs. All drugs are referred to by their generic names. Results Drugs can reduce nutrient intake in several ways and can be broadly classified as: (i) drugs that reduce oral intake; (ii) drugs that alter nutrient absorption and (iii) drugs that affect nutrient metabolism. In this review the mechanisms by which drugs can alter nutritional status are discussed, with specific examples of drug therapy and associated symptoms of deficiencies. Conclusions Patients at high risk of experiencing the effects of drug-induced nutrient deficiencies are the elderly and chronically ill. Recommendations made for methods of intervention include counselling and annotations on drug prescriptions.