The aim of this study was to evaluate the biological and sleep-promoting effects of combined γ-aminobutyric acid (GABA) and 5-hydroxytryptophan (5-HTP) using caffeine-induced sleepless fruit flies, ICR mice, and Sprague-Dawley rats.

Video-tracking analysis was applied to investigate behavioral changes of Drosophila melanogaster . Pentobarbital-induced sleep test and electroencephalogram (EEG) patterns were used for analysis of sleep latency, duration, and quantity and quality of sleep in vertebrate models.

Administration of combined GABA/5-HTP could significantly reverse the caffeine induced total distance of flies ( P < 0.001). Also, individually administered and combined GABA/5-HTP significantly increased the total sleeping time in the caffeine-induced sleepless ICR mice ( P < 0.001). In the caffeine-induced sleepless SD-rats, combined GABA/5-HTP showed significant differences in sleep quality between individual amino acid administrations ( P < 0.05).

Taken together, we identified inhibitory effects of combined GABA/5-HTP in locomotor activity, sleep quantity and quality in caffeine-induced sleepless models, indicating that combined GABA/5-HTP may be effective in patients with insomnia by providing sufficient sleep.