FIELD : medicine.SUBSTANCE : invention relates to medicine, namely to dentistry and dermatology, and can be used for the treatment of oral lichen planus. To do this, inject a solution of photoditazin prepared based on 1.4 mg/kg of body weight of a patient and dissolved in 200 ml of 0.9?% sodium chloride solution, which is administered by an intravenous injection through 30 minutes in a darkened room, then 2 hours after the photosensitizer is injected, a laser irradiation session of the pathologically changed oral tissues is performed with a laser medical apparatus with a wavelength of 661–668 nm, a power of 350–400 mW for 10–15 minutes, while the course is 2–3 procedures with an interval of 4 to 7 days.EFFECT : method allows to increase the effectiveness of treatment of severe forms (erosive-ulcerative and bullous) of lichen planus, reduce the frequency of relapses while reducing the drug load on patients and improve the quality of life of patients.1 cl, 5 dwg