How does this medication work? What will it do for me?

Propylthiouracil belongs to the class of medications called antithyroid medications. It is used to treat an overactive thyroid gland that is producing too much thyroid hormone (sometimes referred to as hyperthyroidism). It works by decreasing the production of thyroid hormone.

Signs of improvement should be seen within 3 weeks of the start of treatment. Propylthiouracil usually needs to be taken for a period lasting between 6 months and 3 years.

Your doctor may have suggested this medication for conditions other than the ones listed in these drug information articles. As well, some forms of this medication may not be used for all of the conditions discussed here. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

What form(s) does this medication come in?

50 mg
Each white, phi-marked, scored tablet contains propylthiouracil 50 mg. This medication does not contain gluten, lactose, or tartrazine.

100 mg
Each white, phi-marked, scored tablet contains propylthiouracil 100 mg. This medication does not contain gluten, lactose, or tartrazine.

How should I use this medication?

The usual adult starting dose of propylthiouracil is 50 mg to 100 mg every 8 hours, with increases as necessary up to a maximum of 500 mg daily or as directed by your doctor. When doses larger than 300 mg per day are needed, the medication should be taken every 4 to 6 hours. Children's doses are based on their body weight.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose or schedule different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. This medication should not be stopped suddenly but should be withdrawn over a period of 1 to 2 months under the direction of your doctor.

If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

Who should NOT take this medication?

Do not take propylthiouracil if you:

  • are allergic to propylthiouracil or any ingredient of the medication
  • are breast-feeding

What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

  • dizziness
  • nausea
  • stomach pain
  • vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

  • backache
  • black, tarry stools
  • blood in urine or stools
  • increase in bleeding or bruising
  • increase or decrease in urination
  • numbness or tingling of fingers, toes, or face
  • pain, swelling, or redness in joints
  • pinpoint-sized red spots on skin
  • skin rash
  • swelling of feet or lower legs
  • swollen lymph nodes
  • swollen salivary glands
  • symptoms of liver problems (such as yellow eyes or skin, abdominal pain, pale stools, dark urine, itching, nausea, or fatigue)

Stop taking the medication and seek immediate medical attention if any of the following occur:

  • cough
  • fever or chills
  • general feeling of discomfort, illness, or weakness
  • hoarseness
  • mouth sores
  • shortness of breath
  • throat infection

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Hypothyroidism: Your dose of propylthiouracil will be reduced or temporarily discontinued by your doctor if signs of hypothyroidism (such as weight gain, clumsiness, and intolerance of cold temperatures) occur during treatment.

Kidney problems: If you have kidney problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Medical symptoms: Contact your doctor if fever, sore throat, unusual bleeding or bruising, or skin rash occur while using this medication.

Size of thyroid gland: Tell your doctor if the size of your thyroid gland increases during treatment with propylthiouracil. You may need a lower dose of the medication.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication passes into breast milk. If you are a breast-feeding mother and are taking propylthiouracil, it may affect your baby. Women who take propylthiouracil should not breast-feed.

What other drugs could interact with this medication?

There may be an interaction between propylthiouracil and any of the following:

  • beta-blockers (e.g., atenolol, metoprolol, propranolol)
  • digoxin
  • medications that contain iodine
  • theophyllines (e.g., aminophylline, oxtriphylline, theophylline)
  • warfarin

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.