Two medicines, side by side
Levothyroxine vs propylthiouracil
Levothyroxine is labeled for hypothyroidism; propylthiouracil has no indication this site maps. Their labels share no use, so they are not alternatives to each other. Drugs@FDA records approvals of levothyroxine since 2000 and of propylthiouracil since 1947. Pharmacies paid $0.0588 per levothyroxine 112 mcg tablet and $0.269 per propylthiouracil 50 mg tablet (NADAC, October 7, 2026); the strengths differ, so the two prices are not like for like. In FDA's classes, levothyroxine is a l-thyroxine and propylthiouracil a thyroid hormone synthesis inhibitor.
Check it at the source: the levothyroxine FDA label on DailyMed (effective February 20, 2024); the propylthiouracil FDA label on DailyMed (effective August 27, 2026).
Highlights of the levothyroxine record
Levothyroxine (Synthroid) · label of February 20, 2024
NOT FOR TREATMENT OF OBESITY OR FOR WEIGHT LOSS Thyroid hormones, including SYNTHROID, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction.
Used for
From the label: indicationsHypothyroidism SYNTHROID is indicated in adult and pediatric patients, including neonates, as a replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism. […]
On the market
- Earliest approval on file
- August 21, 2000
- Generic labelers
- 36 labelers
- Pharmacy cost
- $0.0588 per tablet
Supply and safety
- Shortage
- No current entry
- Recalls
- 128
Highlights of the propylthiouracil record
Propylthiouracil · label of August 27, 2026
Severe liver injury and acute liver failure, in some cases fatal, have been reported in patients treated with propylthiouracil. These reports of hepatic reactions include cases requiring liver transplantation in adult and pediatric patients. Propylthiouracil should be reserved for patients who cannot tolerate methimazole and in whom radioactive iodine therapy or surgery are not appropriate treatments for the management of hyperthyroidism.
Used for
From the label: indicationsPropylthiouracil is indicated: in patients with Graves’ disease with hyperthyroidism or toxic multinodular goiter who are intolerant of methimazole and for whom surgery or radioactive iodine therapy is not an appropriate treatment option to ameliorate symptoms of hyperthyroidism in preparation for thyroidectomy or radioactive iodine therapy in patients who are intolerant of methimazole
On the market
- Earliest approval on file
- July 28, 1947
- Generic labelers
- 5 labelers
- Pharmacy cost
- $0.269 per tablet
Supply and safety
- Shortage
- No current entry
- Recalls
- 1
Source: FDA drug labels via openFDA (Levothyroxine label of February 20, 2024, Propylthiouracil label of August 27, 2026); NDC Directory, Drugs@FDA, NADAC, FDA shortages and recalls (October 8, 2026)
How do levothyroxine and propylthiouracil differ on the record?
In FDA's classes, levothyroxine is a l-thyroxine and propylthiouracil a thyroid hormone synthesis inhibitor.
Both labels carry a boxed warning; the records quote them.
Generics: levothyroxine since 2002; propylthiouracil since 1970 (Drugs@FDA).
| Levothyroxine | Propylthiouracil | |
|---|---|---|
| Labeled for | Hypothyroidism | n/a |
| Pharmacologic class | l-Thyroxine | Thyroid Hormone Synthesis Inhibitor |
| How it works (label) | Thyroid hormones exert their physiologic actions through control of DNA transcription and protein synthesis. Triiodothyronine (T3) and L-thyroxine (T4) diffuse into the cell nucleus and bind to thyroid receptor proteins attached to DNA. | n/a |
| Half-life (label) | n/a | n/a |
| Earliest approval on file (Drugs@FDA) | August 21, 2000 | July 28, 1947 |
| First generic approved | June 5, 2002 | July 24, 1970 |
| Generic labelers (NDC) | 36 labelers | 5 labelers |
| Pharmacy cost (NADAC, each one's most listed form; strengths differ) | $0.0588 per tablet (Levothyroxine 112 mcg tablet) | $0.269 per tablet (Propylthiouracil 50 mg tablet) |
| 12-month price change | -12% | -12% |
| Boxed warning | Yes | Yes |
| Shortage now | No current entry | No current entry |
| Recalls recorded | 128 | 1 |
| FAERS reports (a report is not proof of cause; counts follow how widely a medicine is used) | 300,456 | 2,050 |
| DEA schedule | none | none |
Source: Drugs@FDA, FDA NDC Directory, CMS NADAC of October 7, 2026, FDA shortages and recalls, FAERS via openFDA (FDA files October 8, 2026)
Do their labels mention each other?
Levothyroxine label, drug interactionsDrug or Drug Class: Amiodarone Beta-adrenergic antagonists - (e.g., Propranolol > 160 mg/day) Glucocorticoids -(e.g., Dexamethasone ≥ 4 mg/day) Propylthiouracil (PTU); Effect: Administration of these enzyme inhibitors decrease the peripheral conversion of T 4 to T 3, leading to decreased T 3 levels. However, serum T 4 levels are usually normal but may occasionally be slightly increased. …
Source: FDA drug labels via openFDA
What next?
- Alternatives to levothyroxine
- every medicine labeled for the same conditions