The aim of the study was to assess the quality of sleep, cognitive functions and the effect of insomnia on work and social adaptation in young patients suffering from primary insomnia (in accordance with the DSM-5 and ICD-10 criteria for insomnia) and their dynamics under the influence of Sonmelate forte.Materials and methods. The study involved 23 patients (mean age – 41,3±2,8 years) with chronic primary insomnia and a duration of insomnia disorders of 7,79±2,4 months. The control group consisted of 20 healthy individuals (mean age 40,6±2,3 years) with no insomnia. In order to treat insomnia, patients took Sonmelate Forte (combination of 5 mg of melatonin immediate and 5 mg of melatonin sustained release) 1 tablet 30 minutes before sleep for 30 days.Results of the study. Chronic primary insomnia in young patients contributes to the development of mild manifestations of cognitive dysfunction in the form of impaired short-term visual and auditory memory, decreased concentration, stability and increased attention depletion, and also contributes to the development of emotional disturbances (anxiety, depression), work and socialmaladjustment. Sonmelat Forte is an effective and safe means of treating chronic primary insomnia in young patients, helping to reduce sleep latency, night and early awakenings, increase night sleep duration and decrease daytime sleepiness, promotes regression of mild cognitive dysfunction in young patients (improvement in short-term visual and auditory memory, attention span), improves the patient’s emotional state and daytime functioning by decreasing daytime oh sleepiness and general fatigue, contributing, thus, to increase the level of social and work adaptation.