Randomized, Double-blind, Placebo-controlled Trial of the Efficacy and Safety of Tianeptine in the Treatment of Covid Fog Symptoms in Patients After COVID-19.

Inclusion Criteria: * Written informed consent from the patient to participate in the clinical trial. * Age ≥ 18 years. * History of COVID-19 infection confirmed by a positive SARS-CoV-2 test result by RT- PCR or positive antigen test. * Subjective patient-reported cognitive decline after COVID-19 infection at Screening. * Cognitive dysfunction found at Screening, defined by the Montreal Scale for the Assessment of Cognitive Function (MoCA) as a score of less than 26. * Use of effective contraception by women of childbearing potential. Exclusion Criteria: * Hypersensitivity to tianeptine. * Hypersensitivity to fluorodesoxyglucose (FDG). * History of allergy to drugs or other substances, which, in the Investigator's opinion, is a contraindication to participation in the study. * History of stroke. * Ever undergone and planned brain surgery at the time of the study. * Previously diagnosed organic damage to the central nervous system. * Diagnosed organic mental disorder. * Diagnosed bipolar affective disorder. * Diagnosed psychotic disorder. * History of active depressive episode, including those diagnosed at the time of study eligibility, requiring antidepressant treatment. * Diagnosed mental retardation. * Bipolar affective disorder in a first-degree relative. * Uncontrolled diabetes mellitus. * Severe renal failure with eGFR \< 30ml/min/1.73 m2. * cirrhosis of liver Severe liver cirrhosis (Child-Pugh class C ). * Claustrophobia. * Diagnosed chronic diseases that significantly worsen the patient's prognosis and quality of life, which, in the Investigator's opinion, may adversely affect the patient's participation in the study. * Active or past malignancy within the past 5 years, except for basal cell carcinoma of the skin and cervical cancer in situ in patients who have received radical treatment. * Active viral, bacterial, fungal, tuberculous, or parasitic infection. * History or presence of other relevant diseases which, in the Investigator's opinion, is a contraindication to participation in the study. * Positive pregnancy test performed on women of childbearing potential at screening or Visit 1. * Taking medications: 1. Non-selective MAO inhibitors within 14 days prior to screening, 2. Mianserin during screening. * Significant difficulty with peripheral venous cannulation. * Positive history of alcohol, drug, and psychoactive abuse/dependence. * Pregnancy or planning a pregnancy during the study period. * Breastfeeding or planning to breastfeed during the study period. * Current participation in another clinical trial. * Lack of patient compliance.