Introduction. The problem of pathology of internal organs comorbidity with obesity has become particularly relevant in recent years. The association of obesity with gastrointestinal pathology, in particular, irritable bowel syndrome has not been studied enough. The role of melatonin in the development of these diseases and the possibility of using its synthetic forms in their treatment has drawn the attention of researchers in recent years. Objective-to study the effect of synthetic melatonin on blood pressure, autonomic status, sleep quality, the level of ghrelin and serotonin in patients suffering from obesity combined with arterial hypertension and irritable bowel syndrome with constipation. Material and methods. The study involved 78 patients, of which 34 were diagnosed with irritable bowel syndrome with constipation combined with obesity, and 54 of those who suffered obesity, irritable bowel syndrome combined with arterial hypertension. Patients of each group were divided into two subgroups depending on the treatment complex, one of which received standard therapy, and in the case of combination with arterial hypertension, they also received three component antihypertensive therapy, while the other two received synthetic melatonin before the standard therapy. Results. There was a more significant decrease in average daily systolic and diastolic blood pressure values under the influence of therapy with the inclusion of vitae-melatonin and a significant decrease in the number of patients with a non-dipper and night-picker blood pressure profile. The more positive influence of comprehensive therapy with the inclusion of melatonin on parameters of heart rate variability and its quality was noted. The administration of melatonin combined with a standard therapy led to an increase in the frequency of the bowel movement, approaching serotonin in the serum to normal rates and a decrease in the postprandial level of ghrelin without changes in its fasting concentration. Conclusions. The obtained results are indicative of the positive effect of melatonin on obesity combined with irritable bowel syndrome with constipation and arterial hypertension.