John Larsen

Intake of St John's wort improves the glucose tolerance in healthy subjects who ingest metformin compared with metformin alone

AIMS Our objective was to investigate the steady-state pharmacokinetic and pharmacodynamic interaction between the antidepressive herbal medicine St Johns wort and the antidiabetic drug metformin. METHODS We performed an open cross-over study in 20 healthy male subjects, who received 1 g of metformin twice daily for 1 week with and without 21 days of preceding and concomitant treatment with St Johns wort. The pharmacokinetics of metformin was determined, and a 2 h oral glucose tolerance test was performed. RESULTS St Johns wort decreased the renal clearance of metformin but did not affect any other metformin pharmacokinetic parameter. The addition of St Johns wort decreased the area under the glucose concentration-time curve [702 (95% confidence interval, 643-761) vs. 629 min*mmol/L (95% confidence interval, 568-690), P = 0.003], and this effect was caused by a statistically significant increase in the acute insulin response. CONCLUSIONS St Johns wort improves glucose tolerance by enhancing insulin secretion independently of insulin sensitivity in healthy male subjects taking metformin.