The textbook is devoted to the practical aspects of clinical pharmacology of drugs and modern principles of rational pharmacology. Based on a large amount of factual material, the main principles of rational selection of drugs, application and dosage, analysis of side effects are summarized. Special attention has been paid to drug interactions, which are the most common cause of problems during drug treatment. Situations when it is necessary to adjust the prescription of drugs or to carry out therapeutic drug monitoring have also considered. The manual is intended for students of higher medical educational institutions, pharmaceutical institutes and faculties. It may also be useful for clinical pharmacologists and practicing professionals in the field of healthcare.