Two medicines, side by side
Levothyroxine vs liothyronine
Levothyroxine and liothyronine are both labeled for hypothyroidism. Drugs@FDA records approvals of levothyroxine since 2000 and of liothyronine since 1956. Pharmacies paid $0.0588 per levothyroxine 112 mcg tablet and $0.294 per liothyronine sod 25 mcg 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 liothyronine a l-triiodothyronine.
Check it at the source: the levothyroxine FDA label on DailyMed (effective February 20, 2024); the liothyronine FDA label on DailyMed (effective June 4, 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 liothyronine record
Liothyronine (Cytomel) · label of June 4, 2026
NOT FOR TREATMENT OF OBESITY OR FOR WEIGHT LOSS
Thyroid hormones, including LIOTHYRONINE SODIUM, 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: indicationsLiothyronine sodium is an L-triiodothyronine (T3) indicated for: • Hypothyroidism: As replacement in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism ( 1.1 ) • Pituitary Thyroid-Stimulating Hormone (TSH) Suppression: As an adjunct to surgery and radioiodine therapy in the management of well-differentiated thyroid cancer ( 1.2 ) • Thyroid Suppression Test: […]
On the market
- Earliest approval on file
- May 8, 1956
- Generic labelers
- 17 labelers
- Pharmacy cost
- $0.294 per tablet
Supply and safety
- Shortage
- No current entry
- Recalls
- 11
Source: FDA drug labels via openFDA (Levothyroxine label of February 20, 2024, Liothyronine label of June 4, 2026); NDC Directory, Drugs@FDA, NADAC, FDA shortages and recalls (October 8, 2026)
How do levothyroxine and liothyronine differ on the record?
In FDA's classes, levothyroxine is a l-thyroxine and liothyronine a l-triiodothyronine.
Both labels carry a boxed warning; the records quote them.
Generics: levothyroxine since 2002; liothyronine since 1982 (Drugs@FDA).
| Levothyroxine | Liothyronine | |
|---|---|---|
| Labeled for | Hypothyroidism | Hypothyroidism |
| Pharmacologic class | l-Thyroxine | l-Triiodothyronine |
| 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. | 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. |
| Half-life (label) | n/a | The biological half-life is about 2-1/2 days. |
| Earliest approval on file (Drugs@FDA) | August 21, 2000 | May 8, 1956 |
| First generic approved | June 5, 2002 | January 25, 1982 |
| Generic labelers (NDC) | 36 labelers | 17 labelers |
| Pharmacy cost (NADAC, each one's most listed form; strengths differ) | $0.0588 per tablet (Levothyroxine 112 mcg tablet) | $0.294 per tablet (Liothyronine sod 25 mcg tablet) |
| 12-month price change | -12% | -14% |
| Boxed warning | Yes | Yes |
| Shortage now | No current entry | No current entry |
| Recalls recorded | 128 | 11 |
| FAERS reports (a report is not proof of cause; counts follow how widely a medicine is used) | 300,456 | 8,659 |
| 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?
Liothyronine label, drug interactionsOther drugs: Amiodarone; Amiodarone inhibits peripheral conversion of levothyroxine (T4) to triiodothyronine (T3) and may cause isolated biochemical changes (increase in serum free-T4, and decreased or normal free-T3) in clinically euthyroid patients.
Source: FDA drug labels via openFDA
What next?
- Alternatives to levothyroxine
- every medicine labeled for the same conditions