Aim: to investigate the factors of bacterial virulence of oral microbiotopes against the background of long-term experimental action of an opioid analgesic. Materials and Methods: The study was performed on 72 white outbred rats, which were injected “Nalbuphine” with a gradual increase in dose for 12 weeks. The microbial composition and virulence factors of bacteria in the microbiotopes of the oral cavity were studied. Results: At the end of the 4th week of opioid exposure, the appearance of hemolytic escherichia was noted. At the end of the 8th week the appearance of capsular bacteria Klebsiella was registered, as a virulence factor. The production of staphylococcal virulence factors – lecithinase, was noted. At the end of the 12th week of opioid use, the appearance of phycomycete fungi was noted, Gram-negative diplococci, Klebsiella, Hemolytic Escherichia coli and Pseudomonas aureginosa. These changes indicated the development of dysbiotic changes, as well as the gradual formation of foci of the inflammatory process in the oral cavity. Conclusions: In the short-term stages of opioid exposure, changes in biocenoses were manifested in an increase in the contamination of certain types of microorganisms. In the long-term effects of the opioid, the activation of bacterial elements of the microbiocenosis was revealed, which were characterized by increased expression of virulence factors. At the later stages of opioid exposure, the predominance of gram-negative microflora and the activation of cytotoxic action against the background of suppressed activity of the body’s protective response were established.