Abstract

Very large individual differences in the degree of wakefulness (delay of sleep onset) produced by caffeine were demonstrated unequivocally in a group of 20 subjects given caffeine (300 mg) or placebo before bedtime on 10 successive weeknights. Differences in the extent to which caffeine disturbed the soundness of sleep were also observed.

Subjects who habitually drink most coffee tended to report sleeping more soundly than usual on placebo nights and less soundly after caffeine, indicating some chronic disturbance of sleep by caffeine in these individuals.

Absorption of caffeine (300-mg dose) was essentially complete in most subjects, so that no major differences in plasma levels occurred. Plasma levels declined at comparable rates in all subjects. Individual differences in sensitivity presumably arise primarily from intrinsic differences in responsiveness to caffeine at sites of action in the brain, rather than from differences in absorption, distribution, or metabolism of the drug.