Objective — to study changes in the parameters of endogenous intoxication using the level of substances of low and medium molecular weight in the oral fluid in patients with catarrhal stomatitis, which got developed after the acute drug poisoning. Material and methods. To determine the degree of intoxication, we studied the concentrations of low and medium molecular weight substances (SLMMW) in the oral fluid of patients. We studied the saliva of 20 patients (13 men and 7 women, average age 39 years). The control was done against the oral fluid of 10 healthy individuals. The studies were conducted in a control group consisting of 10 healthy individuals with intact oral mucosa and two groups of patients (20 patients in total) with drug poisoning. The first of these two groups of patients included 8 individuals without pathological changes in the oral mucosa, while the second group consisted of 12 patients diagnosed with catarrhal stomatitis that developed after acute drug poisoning. Results. It became known that endogenous intoxication develops in the oral fluid of patients with acute drug poisoning, which is manifested by a statistically significant increase in the content of SLMMW in comparison with practically healthy individuals (15.3%). And the total level of SLMMW in the oral fluid of patients with acute drug stomatitis and catarrhal stomatitis has increased by 42.3% relative to the data of practically healthy individuals. Conclusion. Studies have shown the need for monitoring the oral cavity in patients with acute drug poisoning, with the aim of timely detection of pathologies of the oral mucosa in them and the appointment of complex treatment.