BMA Concise Guide to Medicine & Drugs


Brand name None

Used in the following combined preparations None


Drug group Drug for thyroid disorders

Overdose danger rating Medium

Dependence rating Low

Prescription needed Yes

Available as generic Yes


Propylthiouracil is an antithyroid drug that suppresses formation of thyroid hormones and is used to manage overactivity of the thyroid gland (hyperthyroidism). In Graves’ disease (the most common cause of hyperthyroidism) a course of propylthiouracil alone or combined with thyroxine (so-called “block and replace” therapy) – usually given for 6–18 months – may cure the disorder. In other conditions, propylthiouracil is given until other treatments, such as surgery or radioiodine, take effect. If other treatments are not possible or are declined by the patient, propylthiouracil can be given long-term. It is the treatment of choice for hyperthyroidism in the first trimester of pregnancy. The full effect of the drug may take several weeks, and beta blockers may be given during this period to control symptoms.

The most important adverse effect is a reduction in white blood cells (agranulocytosis), increasing the risk of infection. Although this is rare, if you develop a sore throat, mouth ulcers, or a fever, you should see your doctor immediately to have your white blood cell count checked.


Your drug prescription is tailored for you. Do not alter dosage without consulting your doctor.

How taken/used Tablets.

Frequency and timing of doses 1–3 x daily.

Dosage range Initially 200–400mg daily. Usually the dose can be reduced to 50–150mg daily.

Onset of effect 10–20 days. Full beneficial effects may not be felt for 6–10 weeks.

Duration of action 6–8 hours.

Diet advice Your doctor may advise you to avoid foods that are high in iodine.

Storage Keep in original container at room temperature out of the reach of children. Protect from light.

Missed dose Take as soon as you remember. If your next dose is due within 3 hours, take a single dose now and skip the next.

Stopping the drug Do not stop the drug without consulting your doctor; stopping the drug may lead to a recurrence of hyperthyroidism.

Exceeding the dose An occasional unintentional extra dose is unlikely to cause problems. Large overdoses may cause nausea, vomiting, and headache. Notify your doctor.


The most common adverse effects of propylthiouracil are nausea, vomiting, joint pain, headache, rash, and itching. Discuss with your doctor if nausea and vomiting are severe or if any of these other symptoms occur. The most important side effects are jaundice and a rare life-threatening reduction in white blood cells (agranulocytosis), which may be indicated by sore throat, fever, or mouth ulcers. If you develop jaundice or any of these other symptoms, you should stop taking the drug and contact your doctor immediately.


Anticoagulants Propylthiouracil may reduce the effects of oral anticoagulants.


Be sure to tell your doctor if:

· You have long-term liver or kidney problems.

· You are pregnant.

· You are taking other medicines.

Pregnancy Prescribed with caution. Risk of goitre and thyroid hormone deficiency (hypothyroidism) in the newborn infant if too high a dose is used. Discuss with your doctor.

Breast-feeding The drug passes into the breast milk and may affect the baby. Discuss with your doctor.

Infants and children Not recommended under 6 years. Reduced dose necessary in older children.

Over 60 No special problems.

Driving and hazardous work No problems expected.

Alcohol No known problems.


Propylthiouracil may rarely cause a reduction in the number of white blood cells.

Monitoring Periodic tests of thyroid function are usually required. If you have a sore throat, fever, or mouth ulcers, your white blood cell count must be checked.