Cyclosporine -- This drug, which is usually taken to prevent rejection of a transplanted organ, suppresses the immune system. Peppermint oil may slow down the rate at which the body breaks down cyclosporine, meaning more if it stays in your bloodstream. Do not take peppermint oil if you take cyclosporine.

Drugs that reduce stomach acid -- If peppermint capsules are taken at the same time as drugs that lower the amount of stomach acid, then the enteric-coated peppermint capsules may dissolve in the stomach instead of the intestines. This could mean the effects of peppermint are lessened. Take peppermint at least 2 hours before or after an acid-reducing drug. Antacids include:

• Famotidine (Pepcid)
• Cimetidine (Tagamet)
• Ranitidine (Zantac)
• Esomeprazole (Nexium)
• Lansoprazole (Prevacid)
• Omeprazole (Prilosec)