Caffeine, the most widely used central nervous system stimulant, is ingested in coffee, tea, chocolate or some non-alcoholic drinks. The aim of this study was to investigate the effect of caffeine intake on cerebral blood flow (CBF) using transcranial Doppler ultrasonography. Twenty adult volunteers had their heart rate, blood pressure,end-tidalCO2,and cerebral blood flow velocities in both middle cerebral arteries measured before and 30 minutes after caffeine intake (300 mg). CBF decreased by 19.3 % from baseline. Cerebral blood flow corrected to et-CO2 = 40mmHg decreased 10 to 19.3 %. Caffeine is a potent cerebral vasoconstrictor due to its antagonism at adenosine receptors.

        Key words: caffeine, transcranial Doppler ultrasonography, cerebral blood flow, adenosine