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Liothyronine

Thyroid Hormones
T3CytomelTriiodothyronine

Overview

Liothyronine, also known as T3, Cytomel, or Triiodothyronine, is a synthetic form of the endogenous thyroid hormone triiodothyronine. It is produced in the thyroid gland through the iodination and coupling of tyrosine residues in thyroglobulin. Liothyronine belongs to the chemical class of iodothyronines, which are crucial for regulating metabolism. As a synthetic compound, it is used in various formulations for therapeutic purposes. Researchers have extensively studied its role in thyroid hormone replacement therapies. Liothyronine plays a critical role in regulating metabolism, heart rate, and body temperature. It is involved in the development and differentiation of cells. Research areas include its effects on metabolic rate, cardiovascular health, and its potential use in treating depression and obesity. Researchers have found that it acts on nuclear thyroid hormone receptors, influencing gene expression and metabolic processes. The mechanism of action of liothyronine involves binding to thyroid hormone receptors in the nucleus of cells, which leads to the modulation of gene expression. This interaction influences various biological pathways, including those involved in metabolism, growth, and development. The activation of these receptors initiates a cascade of events that ultimately affect protein synthesis and cellular metabolism. Liothyronine has a relatively short half-life compared to other thyroid hormones, with a circulating half-life of approximately 24 hours. It is metabolized primarily in the liver and kidneys, with deiodination being a key metabolic pathway. Oral bioavailability is variable, and absorption can be affected by gastrointestinal factors. Clinically, liothyronine is used in the treatment of hypothyroidism and as a diagnostic agent in thyroid function tests. It is approved by regulatory agencies such as the FDA for specific indications. Researchers have observed its use in combination with levothyroxine for certain patients who do not respond adequately to monotherapy. Its regulatory standing varies by country, with specific prescription requirements in place.

Mechanism of Action

Liothyronine acts on nuclear thyroid hormone receptors, modulating gene expression and influencing metabolic processes. This interaction affects protein synthesis and cellular metabolism, impacting various physiological functions.

Molecular Data

FormulaC15H12I3NO4
Molecular Weight650.97 g/mol
CAS Number6893-02-3
PubChem CID5920

Half-Life & Pharmacokinetics

EndogenousCirculating half-life ~24 hours
OralVariable bioavailability due to gastrointestinal factors

Liothyronine has a shorter half-life compared to levothyroxine, necessitating more frequent dosing.

Storage

Temperature

Store at room temperature (15-30°C)

Light

Protect from light

Form

Stable in tablet form

Notes

Avoid exposure to excessive heat and moisture.

Solubility

Liothyronine is poorly soluble in water but soluble in ethanol.

Legal Status

🇩🇪DE

Verschreibungspflichtig (prescription only); not a controlled substance under BtMG.

🇺🇸US

FDA approved for medical use; prescription required.

🇦🇺AU

TGA Schedule 4 (prescription only medicine).

🇬🇧UK

Prescription only medicine (POM) under MHRA regulations.

Legal status information is provided for general reference only and may not reflect the most current regulatory changes. Always verify with official government sources before making any decisions.

6 Research Publications

Treatment Preferences in Patients With Hypothyroidism.

Meta-Analysis

The Journal of clinical endocrinology and metabolism · 2025

Researchers found that a significant number of patients with hypothyroidism prefer combination therapy, which includes liothyronine (L-T3) or desiccated thyroid extract (DTE), over the standard treatment of levothyroxine (L-T4) alone. Specifically, 52% of patients favored combination therapy, highlighting the importance of considering patient preferences in treatment decisions.

  • 24% of patients preferred L-T4 monotherapy.
  • 52% preferred combination therapy with L-T3 or DTE.
  • The preference for combination therapy was consistent across different study designs.
PubMed

Emerging Therapies in Hypothyroidism.

Review

Annual review of medicine · 2024

Researchers observed that while levothyroxine (LT4) works for most hypothyroidism patients, some still experience symptoms. For these individuals, combining LT4 with liothyronine (LT3) can improve their quality of life. Additionally, new treatments like slow-release LT3 and thyroid organoids show promise for future therapies.

  • Combination therapy of LT4 and LT3 is preferred by patients and improves symptoms.
  • New slow-release LT3 formulations are being tested for better stability.
  • Thyroid organoids may restore normal thyroid function in certain conditions.
PubMed

Use of liothyronine (T3) in hypothyroidism: Joint British Thyroid Association/Society for endocrinology consensus statement.

Human

Clinical endocrinology · 2023

Researchers observed that many patients with hypothyroidism continue to experience symptoms despite treatment. The use of liothyronine (T3) alongside levothyroxine remains debated, with no clear benefits shown in studies. The consensus suggests careful evaluation and shared decision-making between patients and clinicians regarding treatment options.

  • Persistent symptoms in hypothyroidism patients are common despite treatment.
  • Liothyronine (T3) combined with levothyroxine has not shown clear benefits in trials.
  • A shared decision-making approach is recommended for considering liothyronine treatment.
PubMed

Optimal Thyroid Hormone Replacement.

Human

Endocrine reviews · 2022

Researchers observed that managing hypothyroidism with levothyroxine can be complex due to factors like patient weight, age, and overall health. They noted that while most patients respond well to levothyroxine, some may benefit from a combination therapy with liothyronine, although this approach needs careful monitoring and is not recommended during pregnancy.

  • Levothyroxine is the standard treatment for hypothyroidism, but maintaining the right dosage can be challenging.
  • Factors such as weight, age, and other health conditions can affect how well patients respond to treatment.
  • Combination therapy with liothyronine may help some patients, but requires careful monitoring and is not suitable for pregnant individuals.
PubMed

Treating hypothyroidism is not always easy: When to treat subclinical hypothyroidism, TSH goals in the elderly, and alternatives to levothyroxine monotherapy.

Review

Journal of internal medicine · 2022

Researchers found that many patients with hypothyroidism feel better with levothyroxine treatment, but some remain dissatisfied, especially if they have mild symptoms. They observed that treatment is often unnecessary for those with mildly elevated thyroid-stimulating hormone (TSH) levels, particularly in older adults, and that alternative treatments may be beneficial for certain patients.

  • Treatment is usually not needed unless TSH exceeds 7.0-10 mIU/L.
  • Many patients with subclinical hypothyroidism may not benefit from treatment.
  • TSH treatment goals vary by age, with higher limits for older adults.
PubMed

Myxedema coma: diagnosis and treatment.

Review

American family physician · 2000

Researchers observed that myxedema coma is a severe and rare complication of hypothyroidism, often triggered by infections. They emphasized the importance of recognizing symptoms of hypothyroidism, such as fatigue and weight gain, to prevent this life-threatening condition.

  • Myxedema coma can occur when the body's mechanisms to cope with low thyroid hormone are overwhelmed.
  • Patients with myxedema coma require intensive care and specific treatments, including intravenous levothyroxine.
  • Family physicians play a crucial role in identifying and managing hypothyroidism to prevent myxedema coma.
PubMed

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This page is for informational and research purposes only. All information is based on published scientific literature. Nothing on this page constitutes medical advice or replaces consultation with a qualified healthcare professional.