The effect of licorice root drink (aqueous extract of Glycyrrhiza glabra Fabaceae) on plasma concentration of verapamil, using rabbits as animal model, was investigated. Two groups of locally inbred New Zealand male rabbits were used. The first group was given a single dose of licorice drink (4 ml/kg body weight) concomitantly with 30 mg/kg verapamil, and the second group was given a daily dose of licorice drink (4 ml/kg body weight) for two weeks, with single doses of verapamil on days, 7 and 14. Single dose treatment resulted in a nonsignificant decrease in mean C(max) by 33.2% (P = 0.41), but in a significant decrease of AUC(0-24) and AUC(0-infinity) by 60.5% and 63.6%, respectively (P = 0.01). First period of multiple dose treatment study (7 days), resulted in a significant reduction in mean C(max), AUC(0-24) and AUC(0-infinity) by 55.0%, 47.0% and 45.7%, respectively (P = 0.02, 0.03 and 0.03, respectively). A more pronounced effect was seen at second period of multiple dose treatment study (14 days), where the corresponding decrease was, 85.4%, 76.8% and 73.3%, respectively (P < 0.01). Mean T(max) was significantly increased 4.2-fold over control period at day 14 of multiple dose study (P = 0.02). In conclusion, licorice root drink decreased verapamil systemic exposure both after single dose and after daily doses for 14 days.