Blood pressure response to the “second cup of coffee”.

Twenty young male coffee-drinkers consumed 150 mg of caffeine in decaffeinated coffee three times a day for 8 days. On days 3, 4, 7, and 8, caffeine or a placebo was administered in the laboratory at 11 A.M., 8 A.M., 11 A.M., and 8 A.M., respectively, in a randomized double-blind crossover design. There was a blood pressure increase relative to the placebo 45 min after taking caffeine at 8 A.M. (5.8/6.5 mm Hg). An increase of 2.4/5.2 mm Hg was seen with the second cup of coffee at 11 A.M. The lower the subject's pre-coffee serum caffeine level, the higher the systolic response, both at 8 A.M. (r = -0.60) and at 11 A.M. (r = -0.62). Because of the pressor effect resulting from habitual caffeine intake, the adverse implications of caffeine use should be considered.