Liothyronine Sodium / Levothyroxine Sodium
Levothyroxine sodium is a synthetic bioidentical form of T4 that the body converts into active T3 as needed, while liothyronine sodium is a synthetic bioidentical form of T3 that provides the active thyroid hormone.
Common dosage forms
Capsule
Oral Tablet
What is Liothyronine Sodium / Levothyroxine Sodium?
Levothyroxine sodium (T4) and liothyronine sodium (T3) are synthetic forms of the two main thyroid hormones, thyroxine and triiodothyronine, used together in thyroid support therapy that may help the body replicate normal thyroid function. Levothyroxine sodium provides a stable source of T4, the inactive hormone that the body converts into T3 as needed, that may support metabolism, energy use, growth, and development. Liothyronine sodium is the active T3 hormone and may act more quickly, directly influencing cellular activity through effects on gene expression, protein synthesis, and metabolic rate.
Combining T4 and T3 may be helpful for patients whose bodies do not adequately convert T4 to T3 or who do not achieve symptom management with T4 alone. This combination may allow providers to tailor the ratio and dosage to match a patient’s hormone levels, symptoms, and metabolic needs. Using both hormones together may offer a more personalized approach to managing hypothyroidism and supporting balanced thyroid activity.
Who May Benefit from Liothyronine Sodium / Levothyroxine Sodium Therapy?
Hypothyroidism
Those who may benefit from thyroid support therapy are those with hypothyroidism, where the thyroid does not produce enough T4 or T3, leading to symptoms such as fatigue, cold intolerance, dry skin, constipation, or slowed metabolism. It may also help those with conditions that impair hormone production—such as Hashimoto’s disease (an autoimmune hypothyroid condition), thyroid surgery, radioactive iodine treatment, or pituitary disorders—who need replacement hormones to maintain normal metabolic function. Additionally, those whose symptoms significantly improve thyroid hormone replacement may benefit from ongoing, monitored therapy to support energy, temperature regulation, and overall well‑being.
Access clinical studies on Liothyronine Sodium / Levothyroxine Sodium
- Schwartz E, Morelli V, Holtorf K. Hormone replacement therapy in the geriatric patient: current state of the evidence and questions for the future–estrogen, progesterone, testosterone, and thyroid hormone augmentation in geriatric clinical practice: part 2. Clin Geriatr Med. 2011 Nov;27(4):561-75. doi: 10.1016/j.cger.2011.07.004. PMID: 22062441.
- Vargas-Uricoechea H, Wartofsky L. LT4/LT3 Combination Therapy vs. Monotherapy with LT4 for Persistent Symptoms of Hypothyroidism: A Systematic Review. Int J Mol Sci. 2024 Aug 25;25(17):9218. doi: 10.3390/ijms25179218.
- Shakir MKM, Brooks DI, McAninch EA, Fonseca TL, Mai VQ, Bianco AC, Hoang TD. Comparative Effectiveness of Levothyroxine, Desiccated Thyroid Extract, and Levothyroxine+Liothyronine in Hypothyroidism. J Clin Endocrinol Metab. 2021 Oct 21;106(11):e4400-e4413. doi: 10.1210/clinem/dgab478. PMID: 34185829; PMCID: PMC8530721.
- Jonklaas J. Optimal Thyroid Hormone Replacement. Endocr Rev. 2022 Mar 9;43(2):366-404.
Access package inserts for Liothyronine Sodium / Levothyroxine Sodium
Commonly Asked Questions
Liothyronine is the synthetic bioidentical form of T3 (triiodothyronine), the body’s active thyroid hormone that works quickly at the cellular level, while levothyroxine sodium is the synthetic bioidentical form of T4 (thyroxine), a storage hormone that the body must convert into T3 before it becomes active. Liothyronine is typically shorter acting than levothyroxine.
Never underestimate the impact stress has on thyroid function. High stress leads to high cortisol levels, potentially preventing the conversion of T4 to T3. In times of illness or inflammation, the stress put on the body can suppress TSH, the primary diagnostic tool in hypothyroidism. This may lead to unreliable lab results; levels of TSH appear within normal range, when in fact there is likely a lack. In aging patients, this may contribute to underdiagnosing hypothyroidism.
An under-functioning thyroid gland is the most common cause of hypothyroidism. Hypothyroidism is a condition in which the thyroid gland, a small butterfly-shaped gland at the base of the neck, doesn’t produce enough T3 and T4. In the autoimmune disease Hashimoto’s Thyroiditis, the body attacks its own thyroid hormone producing cells. The outward signs and symptoms of thyroid imbalance are extensive and may include fatigue and unexplained weight gain.
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