This review highlights the state of cognitive functions in patients with metabolic syndrome, diabetes mellitus at the stage of detection of the underlying disease and after COVID-19. The main links in the pathogenesis of cognitive dysfunction in patients with diabetes are explained, and based on previous studies of SARS-CoV-1 and MERS-CoV, possible mechanisms of cognitive impairment in patients infected with COVID-19 are revealed. Methods for the correction of cognitive disorders with the use of modern nootropics, such as phenibut, are proposed.