This study was carried out in order to establish the scientific basis of the reported ethno-medicinal use of Stachytarpheta cayennensis
(Verbanaceae) as sedative drug. The acute toxicity and barbituric-hypnotic test of the total aqueous (TASC), 50% ethanol (SCCR) and butanol (SCBT), ethylacetate (SCEA) fractions of dried leaves of S. cayennensis
were studied in male rats and mice. The effect of systemic administration of TASC on sleep architecture in rats was also evaluated in Sprague-Dawley rats that were chronically implanted with electrodes for electroencephalogram (EEG) and electromyogram (EMG) recording. The acute toxicity test revealed no lethal effect with doses of SCCR (up to 2000 mg/kg) per oral in rats and doses of TASC (up to 1000 mg/kg and 95 mg/kg) systemically in rats and mice respectively. The extracts significantly (p<0.01) potentiated phenobarbital-induced hypnosis by reducing sleep latency and increasing sleeping time in a dose-dependent manner. Systemic nocturnal administration of single doses (250 and 500 mg/kg) 30 minutes before the onset of dark period of TASC significantly (p<0.05) increased total sleep time, time spent in non-rapid eye movement (NREM) sleep during the 6-h recording period while its effect on REM sleep was biphasic with the higher dose administered. The aqueous extract of Stachytarpheta cayennensis
showed profound effects on sleep-wake stages suggesting the potential sedative effects.