<s>[INST] My husband has an artificial heart valve and is on warfarin. He s got a cold or allergies resulting in runny nose, watery eyes and a headache. Is it safe to take a low dose of benadryl to see if he can get some relief. He only took Tylenol for the headache. [/INST] Hi, thanks for using healthcare magicThere are no known interactions between benadryl and warfarin.He can safely use the two of them together.I hope this helps </s>