 [ Symptoms ] does taking coumadin in lead to thyroid problems [ Disease ] you ask a really interesting question i am going to try to give a brief overview of the curious interaction between anticoagulant drugs like warfarin coumadin and the thyroid for reasons that remain unclear elevated thyroid activity increases the effect of certain oral anticoagulant drugs let is use the inaccurate term blood thinner to illustrate this concept if you are taking warfarin your blood gets thinner  if your thyroid gland also starts cranking out higher levels of hormones or if you increase your dosage of thyroid pills then your blood will become even thinner this can have negative consequences because we obviously do not want a person is blood to be too thin  blood that is too anticoagulated can ooze out of the blood vessels into surrounding tissue like the brain not good however it is probably an overstatement to say that using warfarin can cause thyroid issues i do not believe this is the case but you would be better off to ask an endocrinologist if you are taking warfarin your doctor may want to monitor your thyroid levels some docs do not think the thyroid effect on anticoagulants is a big deal at all while others might be more concerned if you have questions about this you definitely should ask your doctor for an explanation wishing you well