The aim is to investigate changes in the microbiota of dental biofilm at the end of the eighth, tenth and twelfth weeks of experimental opioid exposure. Materials and methods: The study was performed on 36 white outbred adult male rats, which were injected with the opioid analgesic nalbuphine in increasing doses (0,212 – 0,3 mg / kg) during 8, 10 and 12 weeks. Qualitative and quantitative composition of microbiota of dental biofilm was studied using statistical analysis. Results: After eight weeks of opioid exposure, changes in microbiocenosis of dental biofilm of rats were caused by a significant increase in saprophytic and opportunistic microbiota and an appearance of pathogenic species of indicator microbiota with potential periodontopathogenic action. At the end of the tenth week, a significant increase in the quantitative indicators of certain species of opportunistic microbiota and increase in the quantitative composition of pathogenic bacteria were determined. After twelve week of opioid exposure, a significant increase in the quantitative indicators of pathogenic microbiota of dental biofilm was detected. Conclusions: Changes in the qualitative and quantitative composition of the microbiocenosis of the dental biofilm at the end of 8, 10 and 12 weeks of opioid exposure were established, they were manifested by a significant increase in the quantitative indicators of certain species of opportunistic microorganisms and a significant increase in pathogenic microbiota in the dynamics, which led to the progression of dysbiotic changes and purulent-inflammatory process in the oral cavity of rats.