Antithyroid medicines cause your
thyroid gland to make less thyroid hormone.
Why It Is Used
Antithyroid medicine works more
quickly than radioactive iodine therapy. It also does not permanently damage
your thyroid gland.
You may take antithyroid medicine before
you have radioactive iodine treatment or surgery in order to bring your
metabolism to normal, to make you feel better, or to
reduce the chances of more serious problems.
You may also take
antithyroid medicine if you have
Graves' ophthalmopathy and are going to be treated
with radioactive iodine therapy. If you take antithyroid medicine before you
have radioactive iodine treatment, it may prevent your Graves' ophthalmopathy
from getting worse.
How Well It Works
Antithyroid medicines do not
always start working right away. Symptoms usually get better or go away 1 to 8
weeks after you start taking the medicine. It may take as long as 6 months for
your thyroid hormone levels to become normal.
medicines work best if you have mild
hyperthyroidism, if this is the first time you are
being treated for
Graves' disease, if you are younger than 50, or if
your thyroid gland is only swollen a little bit (small goiter).
If your hyperthyroidism comes back after you
have stopped taking the medicine, you can try taking antithyroid medicine
again. But your doctor may recommend radioactive iodine treatment, because
radioactive iodine is more likely to permanently cure your
In some cases, one type of antithyroid medicine
works better than the other.
Methimazole is chosen most often because it can
be given once a day, has fewer side effects, and costs less.
If you are pregnant, propylthiouracil may be safer than
Side effects of antithyroid medicines
Rash and itching.
Liver problems (hepatitis).
Signs of liver problems are yellow eyes or skin, dark urine, severe tiredness,
or pain in your belly.
Low white blood cell count, which can make
it hard for your body to fight infection. If you have a low white blood cell
count, you may become sick easily and have symptoms such as fever,
chills, and a sore throat.
Call your doctor right away if you have any signs of side
effects. Side effects can be serious. But they usually go away after you stop
taking the medicine.
See Drug Reference for a full list of side
effects. (Drug Reference is not available in all systems.)
What To Think About
If you take antithyroid
medicine for a long time, you may develop
hypothyroidism, which means your body is making too
little thyroid hormone.
It is very important to take antithyroid
medicine at the same time every day.
Your doctor will have to
check your thyroid hormone levels frequently to make sure you are taking the
right amount of medicine. If your thyroid hormone levels are too low, your
doctor may prescribe a small amount of thyroid medicine to take along with
your antithyroid medicine.
Your hyperthyroidism is most likely
to come back (relapse) within 6 months after you stop taking medicine. But it can
also come back years later. Be sure to have regular check-ups with your doctor.
If you are
pregnant, your doctor will recommend that you take the smallest effective dose
of antithyroid medicine. After your baby is born, you can safely breast-feed
while taking antithyroid medicine.
Children may be hard to
treat with antithyroid medicine, because they grow so fast and it is hard to
know how much medicine to give them.
How this information was developed to help you make better health decisions.