The article presents and analyzes the results of the pilot study, at which opioid nalbuphine was daily administered in white rats-males of reproductive age (1,5–3,5 – month) for six weeks and one week after discontinuation of therapy. The drug “nalbuphine” was injected intraperitoneally daily 1 per day over 42 days. The data were compared with a control group of intact animals. The study was conducted on 52 animals, which were divided into eight groups.Morphometric study was performed using a system of visual analysis of histological preparations. Dynamics of changes in the external and internal diameters of medium caliber arteries thymus, media and lumen area, Vohenvorta ratio was studied.The increase of the external diameter and reduction of the internal diameter of the medium caliber arteries, increase of the area of media, increase of the area of the lumen, increase of the Vohenvortaratio.The blood vessels are dilated, gaps filled elements of the blood vessels around the swelling, the process of vascular sclerosis.