Some pharmacological interactions between herbal preparations and prescribed medication

Reported pharmacological interactions of common herbal preparations with prescription medication from Medical Journal of Australia Feb 2017


St John’s Wort

  • interferes with cyclosporine used to maintain transplants leading to rejection
  • causes intermenstrual bleeding  for women using the oral contraceptive
  • reduces effectiveness of warfarin
  • reduces bioavailability of theophylline , amitriptyline,, methadone, digoxin
  • potentiates side effects of tricyclic and SSRI antidepressants


Asian Ginseng

  • reduces effectiveness of immunosuppressive drugs
  • increases effects of oral hypoglycaemic ( diabetes ) drugs
  • increases side effects of MAOI antidepressants
  • has accumulative effect on benzodiazepines ( Valium, Serepax)



  • increases liver toxicity of paracetamol
  • increases effects of oral hypoglycaemic ( diabetes ) drugs
  • increases incidence of bleeding in users of anticoagulant medication


Evening Primrose  Oil

  • lowers the seizure threshold  for  epileptics
  • interferes with the action of  some anticonvulsants  including phenytoin ( Dilantin)

Dong Quai

  • potentiates   warfarin