The paper highlights the features of drug use in the legal aspect. It analyzes instructions for medical use of proton pump inhibitors (PPIs) and gastric protective agents. Taking into account the characteristics of indications registered in the instruction, the authors discuss the possibility of using various PPIs. The instruction for medical application is an official document approved by the Ministry of Health, the basis of which is the data of trials carried out by a manufacturer, and it should be a key or fundamental source for a physician in choosing a medication. The use of a drug with no indications given in the manual (the so-called “off-label” use in foreign practice), is a clinical trial of a sort conducted by a physician individually, by taking upon himself/herself a legal liability. If arguments break out over the correct choice of this or that drug in treating the specific patient, the instruction containing the indications for use of specific medications to treat a specific disease is one of the proofs that the physician has correctly chosen the drug or a criterion for skilled medical care. The inclusion of chronic gastritis as a primary and only diagnosis into the primary documentation substantially limits the possibilities of using PPIs. When a PPI is indicated for therapy of erosive gastritis, a formal rationale is contained only in the instruction for use of Controloc. There are no registered indications for PPI use to treat chronic non-erosive gastritis; the gastric protective agent Rebagit is indicated.