The effects of 600 mg of slow release caffeine on mood and alertness.

Background: Caffeine is the most widely used psychostimulant.

Purpose: This study evaluated the pharmacokinetics and effects of mood and alertness of a single oral administration of 600 mg of a slow release caffeine (SRC) on a large group of healthy subjects.

Method: In this double-blind, parallel-group study, 120 young adult males were randomly assigned to either a caffeine group (CG, n = 100) or a placebo group (PC, n = 20). After a normal sleep, each subject took 600 mg of a SRC or a placebo. Circulating caffeine was determined by salivary caffeine assays after acetylation phenotype categorization. Mood, alertness and nocturnal sleep were evaluated by visual analog scales (VAS).

Results: This SRC was well tolerated probably due to its relative low plasmatic Cmax (10.37 micrograms.ml-1). Between CG and PG, there were no differences for alertness, contentedness and sleep quality of the night after treatment (N2) compared to the previous night (N1). VAS scores showed a decrease in calmness in the CG (p < 0.01). Sleep latency in N2 was significantly increased with caffeine (p < 0.01). Calmness, sleep onset latency, quality of sleep onset and overall rating of N2 compared to N1 were correlated with caffeine levels, which were only influenced by tobacco consumption.

Conclusions: Although a single oral dose of 600 mg of a SRC is well tolerated, further evaluation must be done on alertness and pharmacokinetics with fatigued subjects and with females using oral contraceptives.