methimazole vs propylthiouracil
Side-by-side comparison of methimazole and propylthiouracil Data from FDA drug databases (Orange Book, NDC Directory, recalls, shortages) covering 20,000+ approved drugs, plus CMS pricing; see our methodology.
Tapazole
PTU
Methimazole (Tapazole) is a medicine that lowers the amount of thyroid hormone your body makes. It helps treat hyperthyroidism (overactive thyroid).
Propylthiouracil (PTU) is a medicine that treats an overactive thyroid. It helps to lower the amount of thyroid hormone your body makes.
This medicine treats hyperthyroidism, a condition where your thyroid gland makes too much thyroid hormone. Too much thyroid hormone can cause weight loss, fast heartbeat, sweating, and feeling nervous or irritable. Methimazole helps to reduce these symptoms by lowering the amount of thyroid hormone in your body.
PTU treats hyperthyroidism, which is when your thyroid gland makes too much thyroid hormone. It is used for Graves’ disease or toxic multinodular goiter when you cannot take methimazole, or when surgery or radioactive iodine is not a good option for you. PTU can also help control hyperthyroidism symptoms before thyroid surgery or radioactive iodine treatment.
Methimazole stops the thyroid gland from making thyroid hormone. It does this by blocking an enzyme needed to produce the hormones T3 and T4. This helps to bring thyroid hormone levels back to normal.
PTU works by stopping your thyroid gland from making too much thyroid hormone. It does this by interfering with the process that creates these hormones. This helps to reduce the symptoms of hyperthyroidism.
- • Nausea
- • Headache
- • Fatigue
- • Rash
- • Joint pain
- • Skin rash
- • Hives
- • Nausea
- • Vomiting
- • Stomach upset
- Medicine not working 607
- Using medicine for unapproved purpose 463
- Tiredness 426
- Overactive thyroid 384
- Feeling sick to your stomach 372
- The drug is not working 189
- Using the drug for a condition it's not approved for 149
- Overactive thyroid 135
- Baby exposed to the drug during pregnancy 113
- Feeling sick to your stomach 87
Methimazole can cause serious side effects. Talk to your doctor right away if you develop a fever, sore throat, or mouth sores, as these could be signs of a serious blood problem. This medicine may also harm your liver.
PTU can cause severe liver problems, including liver failure, which can be fatal. You should only use PTU if you cannot take methimazole and surgery or radioactive iodine are not right for you. PTU may be the best choice if you need an antithyroid drug during or just before the first 3 months of pregnancy.
Talk to your doctor if you are pregnant or plan to become pregnant. Methimazole can harm your unborn baby. It is also important to discuss breastfeeding with your doctor while taking this medicine.
PTU may be used during the first 3 months of pregnancy if an antithyroid drug is needed. Talk to your doctor about the risks and benefits of taking PTU while pregnant or breastfeeding.
How to Read This methimazole vs propylthiouracil Comparison
methimazole is classified in the Anti-Thyroid Agent drug class, while propylthiouracil sits within the Anti-Thyroid Agent class. Because both drugs share the same classification, they are often considered interchangeable in theory — but clinical outcomes rarely track that cleanly. Both drugs are prescription-only, so a licensed provider must authorize use.
Adverse event totals above are pulled from the FDA's Adverse Event Reporting System (FAERS). For these top-ranked reactions alone, methimazole has 2,252 submissions while propylthiouracil has 673. Those figures reflect cumulative reporting volume — not per-patient risk — so older, widely dispensed drugs typically look worse on count alone. No direct interaction between these two drugs is listed in our FDA-derived dataset, though co-prescription still warrants pharmacist review. Serious warnings, pregnancy guidance, and contraindications can differ even when indications overlap.
A table cannot substitute for clinical judgment. Effectiveness, tolerability, drug-drug interactions with your other medications, kidney and liver function, pregnancy status, insurance formulary, and price all feed into a decision that only a licensed prescriber can make responsibly. Data here is sourced from FDA Structured Product Labels (SPL) and FAERS, both of which update as manufacturers and clinicians submit new information. This page is for educational purposes only, is not medical advice, and should not be used to self-switch between methimazole and propylthiouracil — always consult your physician or pharmacist first.
Important: This comparison is for informational purposes only. Drug effects vary between individuals. Always consult your doctor or pharmacist for personalized medical advice.