Previous human pharmacological and toxicological studies demonstrated advantages of the combination drug Somnium® [SOM, lorazepam (LOR) 1 mg plus diphenhydramine 25 mg] over 1 mg LOR alone, as it showed synergistic effects in hypnotic properties and antagonistic effects in regard to toxicity. In the present double-blind, parallel-group study, hypnotic and anxiolytic effects of SOM were studied in 44 patients with non-organic insomnia related to mild generalized anxiety disorder (GAD), as compared with LOR alone. After a placebo run-in phase of 1 week, they received active treatment (1 tablet SOM or LOR 1 mg) for 4 weeks and thereafter placebo again for 1 week. Clinical evaluations included the physician’s general assessment of efficacy, tolerance and adverse effects, the Hamilton anxiety rating scale (HAMA), the Zung self-rating anxiety scale (SAS) and depression scale, the withdrawal symptom scale (WSS), hematology and blood chemistry. Sleep laboratory evaluations included objective and subjective sleep and awakening quality, measured by polysomnography, self-rating of sleep and awakening quality (SSA) and a psychometric test battery in the morning, as well as measurement of daytime brain function, objectivated by EEG mapping. Physicians’ global evaluation of insomnia demonstrated no changes in the pre-drug placebo period, moderate improvement under both drugs, with a marginal advantage of SOM over LOR in the first 2 weeks, and a return to pre-drug values in the post-drug placebo period. Anxiety improved in observer ratings (HAMA) under both drugs, in self-rating (SAS) under the combination drug only, with the scores returning to pre-drug placebo values after post-drug placebo substitution. There were no significant findings in the self-rating depression scale and the WSS, with the exception of an improvement in the WSS score 4 weeks after SOM, as compared with pre-drug placebo. There were no rebound phenomena. Both drugs were well tolerated – in regard to both adverse effects and laboratory findings. Confirmatory statistics on the polysomnographically recorded target variable latency to sleep onset stage 2 demonstrated a significant shortening of sleep latency after SOM and a significant superiority of the combination drug SOM over LOR after acute dosing, as compared with pre-drug placebo. Descriptive statistics demonstrated further a significant improvement of sleep efficiency and total sleep time after SOM and of wakefulness time and number of awakenings during the total sleep period after both drugs, but no interdrug differences. Sleep architecture remained unchanged. Subjective sleep quality improved with both drugs, morning drowsiness and the total SSA score only with SOM, while LOR was superior to SOM regarding morning somatic complaints. There were neither changes nor interdrug differences in the morning noopsyche. In psychophysiology, critical flicker frequency decreased more under SOM than LOR. After 4 weeks therapy, no significant findings in polysomnography and subjective sleep and awakening were seen, except for an increase in movement time under LOR (tolerance development). In objective awakening quality, psychometry revealed an improvement of reaction time under SOM and a decrease of attention variability and an increase in fine-motor activity under LOR, with an interdrug comparison showing a significant superiority of SOM over LOR in regard to reaction time, reaction time variability and reaction time performance. After placebo substitution, rebound phenomena were seen in polysomnography and subjective sleep and awakening in the 1st night of the SOM group only, which were gone in the 7th placebo night, however. Noopsychic performance remained improved in both groups, with a superiority of SOM to LOR in regard to reaction time and reaction time variability. With a decrease of total power, of absolute delta/theta and alpha power, an increase of absolute beta power, further with an increase of relative delta/theta and beta and decrease of alpha power, as well as a slowing of the DT centroid (C) and acceleration of the alpha, beta and total C, EEG mapping demonstrated changes typical for anxiolytic drugs, which were significantly more pronounced after the combination drug than after LOR only. It is of interest that the drug-induced changes were exactly opposite to the differences measured between GAD patients and normal controls, which suggests a normalization of brain function by the anxiolytics at the receptor