Combined effects of tobacco and caffeine on the components of choice reaction-time heart rate, and hand steadiness.

Eight male smokers were tested under 6 conditions comprising the combinations of 200 mg. caffeine or no caffeine, with no cigarette, one 0.3-mg. nicotine cigarette or one 1.3-mg. nicotine cigarette, for decision time and motor time scores on a choice reaction-time task. Heart rate was monitored from a pretest period throughout the session, and hand steadiness measured on repeated occasions. Decision-time scores were significantly decreased by both caffeine and nicotine, but no interaction was found. The high-nicotine cigarette had the greatest effect. Motor time scores were improved by caffeine only. Both caffeine alone and nicotine alone accelerated the heart rate but in combination appeared to have antagonistic effects. Hand steadiness was significantly impaired by both drugs but with no interaction.