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
All medicines have side effects. But many people don't feel the side effects, or they are able to deal with them. Ask your pharmacist about the side effects of each medicine you take. Side effects are also listed in the information that comes with your medicine.
Here are some important things to think about:
Usually the benefits of the medicine are more important than any minor side effects.
Side effects may go away after you take the medicine for a while.
If side effects still bother you and you wonder if you should keep taking the medicine, call your doctor. He or she may be able to lower your dose or change your medicine. Do not suddenly quit taking your medicine unless your doctor tells you to.
Call 911 or other emergency services right away if you have:
Swelling of your face, lips, tongue, or throat.
Call your doctor if you have:
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.
Common side effects of this medicine include:
Changes in taste.
See Drug Reference for a full list of side
effects. (Drug Reference is not available in all systems.)
What To Think About
It is very important to take antithyroid
medicine at the same time every day.
If the hyperthyroidism comes back, it is most likely to come back within 6 months. Be sure to have regular check-ups with your doctor.
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.
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.
Medicine is one of the many tools your doctor has to treat a health problem. Taking medicine as your doctor suggests will improve your health and may prevent future problems. If you don't take your medicines properly, you may be putting your health (and perhaps your life) at risk.
There are many reasons why people have trouble taking their medicine. But in most cases, there is something you can do. For suggestions on how to work around common problems, see the topic Taking Medicines as Prescribed.
Advice for women
If you are pregnant, breast-feeding, or planning to get pregnant, do not use any medicines unless your doctor tells you to. Some medicines can harm your baby. This includes prescription and over-the-counter medicines, vitamins, herbs, and supplements. And make sure that all your doctors know that you are pregnant, breast-feeding, or planning to get pregnant.
If you take this medicine while you are
pregnant, your doctor will recommend that you take the smallest effective dose. After your baby is born, you can safely breast-feed
while taking antithyroid medicine.
Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.
How this information was developed to help you make better health decisions.