Residual effects of daytime administration of melatonin on performance relevant to flight

There is a general consensus that melatonin possesses time-dependent hypnotic effects, but there is no information yet whether it has residual effects on neurobehavioral performance, especially after daytime administration. In the present study weinvestigated the possible residual effects of 3 mg melatonin on performance relevant to flight and on subjective feelings ofsleepiness, arousal, activation and affect after a daytime nap, as a function of nap length. Fifteen reserve pilots of the Israeli AirForce participated in the study. The experiment consisted of four sessions during which either melatonin or placebo wasadministered at 16:00 h. In two conditions, subjects were allowed to sleep for 2 h (17:00–19:00 h) whereas in the other two onlya 0.5-h nap was allowed. After the naps they started performing a flight simulator task every 2 h. Sleep efficiency significantlyincreased and sleep latency significantly decreased in both melatonin conditions compared to placebo. Flight performance wasonly mildly affected in the 0.5-h nap condition. Subjective assessment of sleepiness significantly differed between the two treatmentconditions, only in the 0.5-h nap condition. Subjects felt sleepier 2–4 h after melatonin administration. To conclude, our datasuggest that administration of melatonin before a brief daytime nap (about 0.5 h) may be associated with mild residual effects onpsychomotor performance and may significantly affect subjective feeling of sleepiness for 2–4 h. © 2002 Elsevier Science B.V. Allrights reserved.