Abstract

Fourteen men from twenty to twenty-five years of age received caffeine or coffee (dosage, 3 or 4 mgm. caffeine per kilogram body weight) once or twice a week and decaffeinated coffee on the intervening days. In certain studies, bouillon was administered as a control beverage.

The blood pressure and the pulse rate after decaffeinated coffee were essentially the same as the blood pressure and the pulse rate after bouillon. After coffee or caffeine, the blood pressure and the pulse rate were altered, although the changes were small and often uncertain. One or two hours after the drugs, the blood pressure was usually increased (5 to 10 mm. Hg), the pulse rate decreased (5 per minute) in certain individuals and increased in others. Twenty-five hours after the drugs, the blood pressure was not changed, but the pulse rate was at times increased.

Motor function was changed by coffee or caffeine, the response to single doses being relatively uniform throughout the two months of experimentation. The performance of a simple movement (target test), was usually improved one or two hours after coffee or caffeine, but impaired in certain individuals particularly twenty-five hours after the drugs. Caffeine exerted a sustained, deleterious influence upon the men's performance of an acquired motor skill. Decaffeinated coffee did not affect performance of this skill. In the target test, the effect of caffeine or coffee upon performance was not apparent later than twenty-five hours after the drugs, but in the acquired motor skill each dose exerted an influence for several days.