Health information to help you understand symptoms. It isn't a diagnosis.
Check symptoms

Propylthiouracil (PTU)

Brand names: PTU

Propylthiouracil lowers thyroid hormone production. It's used for overactive thyroid, mainly in the first trimester of pregnancy or thyroid storm.

Brand namesPTU
Type of medicineAntithyroid medicine
Prescription?Prescription
ImportantThis page is general information, not a prescription. Don't start, stop, or change a medicine without talking to your provider or pharmacist.

Overview

Methimazole is usually preferred because PTU carries a higher risk of liver damage.

What it's used for

  • Overactive thyroid in the first trimester of pregnancy
  • Thyroid storm
  • People who can't take methimazole

How to take it

  • Take it at evenly spaced times, usually several times a day.
  • Keep all blood test appointments.

Your dose depends on your health and other medicines. Always follow your prescription label, and ask your pharmacist if anything is unclear.

Side effects

Common side effects

  • Rash
  • Nausea
  • Joint pain
  • Change in taste
Call 911Fever, sore throat, or mouth sores (possible very low white blood cells)
Call your provider todayYellow skin or eyes, dark urine, loss of appetite, or upper right belly pain (liver damage)

Warnings

  • Boxed warning: severe liver injury, sometimes fatal.

Other medicines, foods, and alcohol

  • It can change how warfarin works.

Tell your provider and pharmacist about every medicine, vitamin, and supplement you take.

Pregnancy and breastfeeding

Preferred over methimazole in the first trimester; often switched afterward.

Missed doses, overdose, and storage

If you miss a dose

Take it as soon as you remember, unless it's almost time for your next dose. Then skip the missed dose. Don't take two doses at once.

If someone takes too much

Call Poison Control at 1-800-222-1222 or get help online at poison.org. Call 911 if the person collapses, has a seizure, has trouble breathing, or can't be woken.

Storing it

Store at room temperature, away from heat and moisture (not in the bathroom), and out of reach of children and pets.

Conditions it's used for

Sources

Last updated 2026-11-13.