Drug interactions and warfarin

What should I know about drug interactions?

Warfarin interacts with many prescription and over-the-counter (OTC) medicines. This also includes certain herbal and natural products. Bring a list of all of the medicines you take to your appointments so they can be checked for drug interactions.

It is very important for you to check with your health-care provider before starting, changing, or stopping any medicine. You may need more frequent INRs or changes in your warfarin dose if you have changes in medicines.

Common OTC medicines that affect warfarin:

The following is a list of some OTC medicines you should not take, unless told by your doctor. These lists are not everything that may interact with warfarin.

It is very important to check with your pharmacist if there are any changes to your medicine while on warfarin.

  • Aspirin
  • Aspirin containing ointments and skin creams (Aspercreme)
  • Pepto-Bismol and Alka-Seltzer
  • Nonsteroidal anti-inflammatory drugs such as ibuprofen (Motrin or Advil) or naproxen (Aleve)
  • Vitamin supplements containing vitamin K

Some common prescription medicines that affect warfarin:

  • Antibiotics, such as sulfamethoxazole/trimethoprim (Bactrim), ciprofloxacin, moxifloxacin (Avelox), metronidazole (Flagyl), rifampin, nafcillin, or erythromycin
  • Yeast or fungal medicines, such as fluconazole
  • Thyroid medicines, such as levothyroxine (Synthroid®)
  • Amiodarone (a heart medicine)
  • Carbamazepine (a seizure medicine)

Some common herbs that can affect warfarin:

  • Coenzyme Q10
  • Garlic
  • Ginkgo biloba
  • St. John’s wort
Last reviewed: 
August 2017

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