The author describes a clinical symptom complex which appears in some patients as a central nervous system side-effect of conventional doses of glaucine, a non-narcotic antitussive preparation, used in outpatients; the symptom complex is described by the author as acute glaucine syndrome (AGS). Clinical manifestations of AGS are the following: 1) very prominent fatigue, which occurs acutely after taking a conventional dose of glaucine and making any kind of professional activity impossible at the moment; 2) very prominent sleepiness, which occurs acutely together with fatigue and is always combined with it; 3) unusual clear but somewhat estranged perception of the environment: the patient sees and understands everything and is oriented well enough, but cannot take a clear and adequate action, 4) full recovery of the impaired functions after the drug is discontinued; 5) AGS recurrence after the drug is taken again. The hallucination-like effect of glaucine, described earlier by the author of this article, which is manifested by bright and colorful visual images, may be considered a facultative AGS component. The author stresses a potential danger of AGS development in persons who control moving mechanisms or vehicles and adduces some clinical observations.