Drug interactions and warfarin

What should I know about drug interactions?

Warfarin interacts with many prescriptions and over-the-counter (OTC) medicines. OTC medicines can be found in the aisles at a pharmacy. This includes vitamins, herbal and natural products. Bring a list of all 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 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.

The following is a list of some OTC medicines you should not take, unless told by your doctor. These lists do not have 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.

Common OTC medicines that affect warfarin:

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

Some common prescription medicines that affect warfarin:

  • Antibiotics, such as sulfamethoxazole/trimethoprim (Bactrim®), ciprofloxacin, moxifloxacin (Avelox®), metronidazole (Flagyl®), rifampin, nafcillin, 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: 
December 2021

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