title: The psychopharmacological and electrophysiological effects of single doses of caffeine in healthy human subjects.
abstract: The effects of single doses of anhydrous caffeine (250 mg and 500 mg) and placebo on physiological, psychological measures and subjective feelings were studied in a double-blind, cross-over study in nine healthy subjects who had abstained from caffeine-containing beverages for 24 h before each occasion. Caffeine and caffeine metabolites in plasma and urine were assayed. Peak plasma concentrations were observed at 1 to 2 h with an approximate half-life of 5 h. The concentrations of the metabolite 1,7-dimethylxanthine increased during the 5 h. The major urine metabolite was 1-methyluric acid. The EEG showed a dose-related decrease in log 'theta' power and a decrease in log 'alpha' power. Other dose-related effects were an increase in skin conductance level (sweat-gland activity) and self rating of alertness. Ratings of headache and tiredness were decreased by the caffeine. The study illustrates the complexities of studying a drug which is widely taken and which is often associated with withdrawal effects.
mesh_terms: D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D001794:Blood Pressure / Q000187:drug effects; D002110:Caffeine / Q000378:metabolism / Q000494:pharmacology*; D004311:Double-Blind Method; D004569:Electroencephalography; D004644:Emotions / Q000187:drug effects; D005260:Female; D005425:Flicker Fusion / Q000187:drug effects; D005712:Galvanic Skin Response / Q000187:drug effects; D006207:Half-Life; D006801:Humans; D008297:Male; D011597:Psychomotor Performance / Q000187:drug effects; D014202:Tremor / Q000139:chemically induced; D014970:Xanthines / Q000378:metabolism
chemical_list: D014970:Xanthines; C008514:methylxanthine; D002110:Caffeine