Background and aim The effects of analgesic drugs on sleep are poorly understood. We investigated short- and medium-term effects of tramadol on sleep structure.

Methods Eight healthy volunteers received a placebo (predrug placebo-night), then, in a randomized, double-blind, cross-over fashion a single oral dose of tramadol 50 mg or 100mg (drug-night), and finally, again a placebo (postdrug placebo-night). Standardized polysomnography (electroencephalogram, electro-oculogram, submental electromyogram) was continuously recorded during placebo- and drug-nights

Results During drug-nights both doses of tramadol significantly increased the duration of stage 2 sleep, and significantly decreased the duration of slow-wave sleep (stage 4). Tramadol 100mg but not 50 mg significantly decreased the duration of paradoxical (rapid eye movement) sleep. In the placebo-night after tramadol 100mg (but not after 50 mg) duration of stage 2 sleep was significantly shorter, and duration of stage 4 sleep was significantly longer compared with the predrug placebo-night. Conclusion In healthy volunteers, a single dose of tramadol 50 mg disturbs sleep in the night of drug application. With 100mg, sleep is disturbed in both the night of drug application and in the subsequent night.