In this article, the application of high resolution NMR spectroscopy to study the effect of therapeutic compounds on cells, tissues and organisms is reviewed. To illustrate how these NMR methods can provide useful information for a better understanding about the mechanism of action of drugs and their interactions with metabolic pathways, the emphasis is placed on most recent work about drug therapeutic intervention in biological models of diseases and in humans. Specifically, the application of NMR spectroscopy to investigate the effect of drugs on the treatment of neurological disorders, cancer, infectious diseases and diabetes is illustrated. In addition, NMR studies of drug-induced toxicity and multinuclear NMR for monitoring drug delivery and catabolism are described. Current progress in NMR instrumentation and methods will continue to improve the sensitivity and maintain this very versatile technique as powerful tool for research in the field of medicinal chemistry.