The Effects of Modafinil and OTC Stimulants on Physical and Cognitive Performance

Performance effects due to insufficient sleep have been documented for decades. Given the prevalence of caffeine as a fatigue countermeasure among military personnel, and the availability of modafinil to select populations, commanders and medical staff have expressed concern over the safety of potentially combining the two alertness aids. The present study compared the combined effects of modafinil and caffeine with those of either substance alone during 35 h of continuous wakefulness. Participants were randomly assigned to one of four groups: modafinil (200mg), caffeine (200mg), modafinil-caffeine (200mg each), or placebo. Following training and baseline, participants received their respective treatment at 2300 (18 h awake). At midnight, participants walked 2 miles on the treadmill with a 30-lb back pack at 3 miles per hour. Cognitive performance, subjective mood, and vital signs were measured every 3 h starting at 0200 for a total of 5 test sessions. The results indicated that modafinil, whether alone or in combination with caffeine, increased alertness and performance across the 37-hour period of continuous wakefulness. When combined with caffeine, the effects were the same for most of the cognitive measures. The subjective side effects and vital signs did not increase with the combination of the two alertness aids, including those vital signs taken while walking on the treadmill. In this select group of study participants, the combination of caffeine with modafinil does not appear to improve or inhibit performance above that with modafinil alone.