What could happen if one takes acetaminophen with codeine while on coumadin?

Acetaminophen (Tylenol) can increase the effect of Coumadin, so it should be discussed with your doctor or pharmacist before taking it. There a many, many drugs that should not be taken with Coumadin, including many herbal medicines/supplements, such as garlic, ginko biloba, chamomile and ginseng. You need to tell your doctor and your pharmacist every med you are taking, including all OTC (over the counter) meds and herbal supplements.