Background: Although peppermint oil and caraway oil are frequently used in herbal drugs for abdominal discomfort and pain, the pharmacological insights into their effects on the gastrointestinal tract are poor.
Methods: The pharmacodynamic effects of 90 mg peppermint oil (WS 1340) and 50 mg caraway oil (WS 1520) on the motility of the stomach and gall-bladder, and on the orocaecal transit time, in comparison with placebo, 10 mg cisapride and 10 mg n-butylscopolamine, were studied in 12 healthy volunteers. The study involved simultaneous ultrasonic determination of gastric and gall-bladder emptying, together with assessment of the orocaecal transit time using the lactulose H2 breath test. The combination of these methods allows three gastrointestinal organs to be studied in one subject simultaneously.
Results: The antral filling time was comparable with placebo, peppermint oil, caraway oil and cisapride, whereas it was significantly shortened (P = 0.04, two-sided paired t-test) with n-butylscopolamine. The gastric emptying time did not differ significantly between placebo, peppermint oil, caraway oil and cisapride, but was significantly prolonged by n-butylscopolamine (P = 0.04, two-sided paired t-test). Complete inhibition of gall-bladder emptying was caused by both oils and n-butylscopolamine. Cisapride significantly shortened gall-bladder emptying compared with placebo (P = 0.02, two-sided signed rank test). The orocaecal transit time was significantly prolonged by peppermint oil (P = 0.004) and n-butylscopolamine (P = 0.002), but not significantly prolonged by caraway oil (P = 0.06); it was significantly shortened by cisapride (P = 0.04, all two-sided paired t-test).
Conclusions: Peppermint oil and caraway oil show a relaxing effect on the gall-bladder and the former slows small intestinal transit. Further studies should investigate the effects of both oils on a maximal contraction stimulus on the gall-bladder, and in patients suffering from motility disorders.