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Propylthiouracil (PTU) is an oral antithyroid tablet used to treat hyperthyroidism, including Graves' disease and toxic multinodular goiter. It lowers thyroid hormone levels by blocking hormone production in the thyroid and reducing the conversion of T4 to the more active T3.
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Propylthiouracil (PTU) is a thionamide antithyroid medication used to treat hyperthyroidism caused by Graves' disease or toxic multinodular goiter in patients who cannot take methimazole or who are not candidates for surgery or radioactive iodine. It is often the preferred antithyroid drug during the first trimester of pregnancy and is also used in thyroid storm. PTU works by inhibiting thyroid peroxidase to block production of thyroxine (T4) and triiodothyronine (T3), and it also reduces the conversion of T4 to T3 in the body. Initial doses typically range from 300 to 400 mg per day divided every 8 hours, with maintenance doses of 100 to 150 mg per day. Common side effects include rash, itching, nausea, stomach upset, joint pain, and changes in taste. PTU carries a boxed warning for severe liver injury, so patients should contact their doctor right away if they develop fatigue, loss of appetite, dark urine, yellowing of the skin or eyes, or pain in the upper right abdomen. Fever, sore throat, or other signs of infection should also be reported promptly, as PTU can rarely lower white blood cell counts.
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Propylthiouracil (PTU) is used to treat hyperthyroidism from Graves' disease or toxic multinodular goiter, most often when methimazole is not tolerated, during the first trimester of pregnancy, or in thyroid storm. Treatment usually starts at 300 to 400 mg per day divided every 8 hours, then is lowered to a maintenance dose of 100 to 150 mg per day once thyroid levels normalize. Your doctor will check thyroid blood tests regularly to adjust the dose.
Common side effects include rash, itching, hives, nausea, vomiting, upset stomach, joint pain, headache, and a change in taste.
Important safety warning: PTU carries a boxed warning for severe liver injury and acute liver failure, which can occur at any time during treatment. Stop taking PTU and contact your doctor right away if you notice fatigue, weakness, loss of appetite, itching, dark urine, pale stools, yellowing of the skin or eyes, or pain in the upper right abdomen. PTU can also rarely cause agranulocytosis, a serious drop in white blood cells, so report fever, sore throat, or mouth sores promptly.
Because of the liver risk, PTU is generally reserved for patients who cannot take methimazole, and many doctors switch pregnant patients to methimazole after the first trimester. PTU may increase the effect of blood thinners such as warfarin, so share a full list of your medications with your doctor and pharmacist.
Thyroid Disorder Treatment
Propylthiouracil (PTU) is an antithyroid medication used to treat hyperthyroidism, a thyroid disorder where the gland makes too much thyroid hormone. It is most often caused by Graves' disease or toxic multinodular goiter. PTU lowers hormone production so symptoms like a racing heart, weight loss, and heat intolerance can improve.
Hyperthyroidism means the thyroid is overactive and makes too much hormone, which can cause a fast heartbeat, weight loss, anxiety, and sweating. Hypothyroidism means the thyroid is underactive, which can cause fatigue, weight gain, and feeling cold. PTU treats hyperthyroidism only. If the dose is too high, thyroid levels can drop too low, so your provider will monitor your blood work.
PTU can ease symptoms of an overactive thyroid, including a rapid or irregular heartbeat, shakiness, nervousness, trouble sleeping, unexplained weight loss, frequent bowel movements, and feeling too warm. Eye symptoms linked to Graves' disease, such as bulging or irritated eyes, may need separate treatment from an eye specialist.
Thyroid disorders are diagnosed with blood tests that measure TSH, free T4, and sometimes T3. Antibody tests can confirm an autoimmune cause like Graves' disease, and an uptake scan or ultrasound may be used in some cases. These same blood tests are repeated during treatment to adjust your PTU dose.
Yes. Graves' disease is the most common autoimmune thyroid disorder that causes hyperthyroidism. The immune system makes antibodies that overstimulate the thyroid. Hashimoto's thyroiditis is the other common autoimmune thyroid disorder, but it causes hypothyroidism instead. Antithyroid medications like PTU and methimazole are used for Graves' disease.
Administration & Dosage
PTU is usually taken by mouth three times a day, about every 8 hours, because it leaves the body quickly. Take it at the same times each day, with or without food. Do not stop taking it unless your provider tells you to.
Treatment often starts at 300 to 400 mg per day, divided into doses every 8 hours. Once thyroid levels return to normal, the dose is usually lowered to a maintenance dose of about 100 to 150 mg per day. Your provider will adjust the dose based on your thyroid blood tests.
Many people start to feel better within a few weeks, but it usually takes about 4 to 8 weeks for thyroid hormone levels to return to normal. Treatment often continues for 12 to 18 months or longer.
Uses & Mechanism of Action
Propylthiouracil, often called PTU, is a prescription antithyroid medication that comes as a 50 mg tablet. It belongs to the same drug class as methimazole.
PTU blocks the thyroid gland from using iodine to make new thyroid hormone. It also reduces the conversion of T4 into T3, the more active form of thyroid hormone, which is one reason it is used in severe cases like thyroid storm.
Methimazole is usually the first choice, but PTU is preferred during the first trimester of pregnancy, in thyroid storm, and for people who cannot tolerate methimazole. Many women switch from PTU to methimazole after the first trimester.
Side Effects & Safety
Common side effects include rash, itching, hives, nausea, upset stomach, joint pain, headache, and a change in taste. Tell your provider if these are bothersome or do not go away.
Yes. PTU has an FDA boxed warning for severe liver injury and acute liver failure, which can happen at any time during treatment. Stop taking PTU and call your provider right away if you notice fatigue, loss of appetite, dark urine, pale stools, yellowing of the skin or eyes, or pain in the upper right abdomen.
PTU can rarely cause agranulocytosis, a serious drop in white blood cells that makes it hard to fight infection. Contact your provider right away if you develop a fever, sore throat, mouth sores, or other signs of infection.
Yes. If the dose is higher than you need, thyroid hormone levels can fall too low. Symptoms of hypothyroidism include fatigue, weight gain, feeling cold, and constipation. Regular blood tests help your provider keep your dose in the right range.
Interactions & Contraindications
PTU may increase the effect of warfarin and raise the risk of bleeding. If you take warfarin, your provider may check your INR more often when starting or changing PTU.
Possibly. As hyperthyroidism improves, doses of medications such as beta blockers, digoxin, and theophylline may need to be lowered. Tell your provider about all medications and supplements you take.
People who have had a serious allergic reaction to PTU should not take it. It is used with extra caution in people with liver disease or those taking other medications that can affect the liver. It is generally not recommended for children because of the liver risk.
Generic & Alternatives
PTU is available as a generic medication. It is commonly referred to by its abbreviation, PTU.
Both are antithyroid medications for hyperthyroidism. Methimazole is taken once daily and has a lower risk of liver injury, so it is usually preferred. PTU is taken every 8 hours and is mainly used in the first trimester of pregnancy, in thyroid storm, or when methimazole is not tolerated.