Anxiolytic and sedative effects of extracts of Hibiscus sabdariffa Linn (family Malvaceae).

Aqueous (A), hydroalcoholic (AE) and ethanolic (E) extracts and fractions of dried calyxes of Hibiscus sabdariffa were evaluated for anxiolytic property using elevated-plus maze (EPM), and sedative properties using ketamine-induced sleep in animal models. The extracts exhibited a dose-dependent increase in the time spent in the open arm with ethanol extracts having the best anxiolytic activity. The extracts at A 5 mg/kg, AE 5 mg/kg and A 50 mg/kg did not cause an increase in time spent in the open arms (p < 0.05) but other doses significantly did when compared with the vehicle control. The fractions of the hydroalcoholic extracts showed no significant anxiolytic activity. Neither the extracts nor the fractions significantly reduced or increased latency to sleep after a single dose except AE 300 (p < 0.01). There was significant reduction in onset of sleep, and increase in sleeping time with A and AE extracts with multiple doses at A 300, AE 50 and AE 300 mg/kg dose groups (p < 0.001, p < 0.01 and p < 0.05 respectively). A reduction in sleeping time after several daily doses of ethanol extracts doses was observed. A single dose of one of the fractions (EAC at 50 mg/kg) caused a significant reduction (p < 0.05) in sleep duration. The study showed that extracts of Hibiscus sabdariffa possess anxiolytic and sedative effects which become more pronounced with administration of repeated doses of the extracts.