What medications can interact with warfarin (Coumadin)?

Foods containing vitamin K affect how Coumadin works. Green leafy vegetables contain a high level of vitamin K. Increased consumption of vitamin K containing foods decrease the blood thinning effect of Coumadin. Reducing the consumption of vitamin K containing foods will increase the effect of Coumadin. To avoid a yo-yo effect in the action of Coumadin, healthcare providers suggest that vitamin K consumption should not vary widely while on Coumadin treatment.

Mohammad Mortada, MD
Cardiology (Cardiovascular Disease)
It is important to keep in mind that several medications can change the effect of warfarin (Coumadin).

Medications or substances that increase INR and risk of bleeding include:
  • Antiarrhythmic medications: amiodarone, propafenone
  • Antibiotics: azithromycin (Zmax, Zithromax), cefazolin (Ancef,
           Kefzol), erythromycin (E-mycin, Ery-Tab, Eryc, E.E.S.,
           Erythrocin), aspirin
  • Alcohol in beverages or cough medicines
  • Beta-adrenergic blockers: propranolol (Inderal)
  • Diabetic agents
  • Herbal supplements
  • Thyroid drugs
Medications that decrease INR and increase the risk of stroke include:
  • Antacids
  • Antianxiety agents
  • Antibiotics: dicloxacillin (Dynapen), nafcillin
  • Cortisone (Cortef)
  • Oral contraceptives
  • Spironolactone (Aldactone)
  • Vitamin C (high dose)
  • Vitamin K (green, leafy vegetables)
Medications or substances that have unpredictable effects:
  • Alcohol
  • Antidepressants
  • Gastric acidity and peptic ulcer agents

Continue Learning about Anticoagulant

Is it safe to stop taking blood thinners for afib before hip surgery?
Dr. Rishi G. Anand, MDDr. Rishi G. Anand, MD
If you suffer from atrial fibrillation (afib) and are taking blood thinners (anticoagulants), you wi...
More Answers
What precautions should I follow when taking blood thinners?
Grant Cooper, MDGrant Cooper, MD
If you are taking warfarin (Coumadin), you already should be having a test regularly to make sure th...
More Answers
What is Praxbind?
Praxbind (idarucizumab) is a medication used to reverse the effects of another medication, Pradaxa (...
More Answers
What does it mean if my child's PT/INR test result is too low?
Stacy Wiegman, PharmDStacy Wiegman, PharmD
If your child's PT/INR test result is too low, it means that her dose of warfarin may not be eno...
More Answers

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.