Thyroid Hormone (T3) Pregnancy: eMC 4.6: Safety during pregnancy is not known; the risk of foetal congenital abnormalities should be weighed against the risk to the foetus of untreated maternal hypothyroidism. Breast-feeding - excreted into breast milk in low concentrations, which may interfere with neonatal screening programmes. No human or animal fertility data.

Liothyronine Sodium (T3)

Brand names: Tertroxin, Thybon Henning

Used in: Thyroid Disorders

Liothyronine is synthetic triiodothyronine (T3), a fast-acting thyroid hormone with a shorter duration of action than levothyroxine. It is reserved for specialist situations such as severe hypothyroidism or myxoedema coma, and is not routinely preferred over levothyroxine for maintenance.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Starting dose 10 or 20 micrograms every 8 hours; usual recommended daily dose 60 micrograms

Route: Oral use only (tablets; a whole tablet may be crushed and dissolved with swirling in a minimum 20 ml of water for 5 minutes, and the entire volume consumed)

Frequency: Starting dose every 8 hours, increased after one week if necessary; usual daily dose of 60 micrograms given in two or three divided doses

eMC SPC 4.2 (Liothyronine Sodium 10 microgram Tablets): 'Adults: Starting dose of 10 or 20 micrograms every 8 hours, increasing after one week, if necessary, to the usual recommended daily dose of 60 micrograms in two or three divided doses.' Other regimens stated in the same section: Myxoedema coma - 60 micrograms given by stomach tube, then 20 micrograms every 8 hours, though 'it is more usual to start treatment with intravenous liothyronine'. Adjunct to carbimazole treatment of thyrotoxicosis - 20 micrograms every 8 hours. Elderly - 5 micrograms daily. Paediatric doses in the SPC are not weight-based: children below 12 years 5 micrograms daily; adolescents 12-17 years initially 10-20 micrograms daily, increased to 60 micrograms daily in 2-3 divided doses - verify against a children's formulary before use. SPC 4.4: monitor TSH during treatment to reduce the risk of over- or under-treatment; baseline ECG is recommended before starting and periodic ECGs during treatment; if metabolism increases too rapidly (diarrhoea, nervousness, rapid pulse, insomnia, tremors, anginal pain), reduce the dose or withhold for 1-2 days and start again at a lower dose; initiate corticosteroid therapy before starting liothyronine in panhypopituitarism or predisposition to adrenal insufficiency.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

Administer liothyronine sodium tablets orally once daily and individual dosage according to patient response and laboratory findings ( 2.1 ) See full prescribing information for recommended dosage for hypothyroidism ( 2.2 ) TSH suppression in well-differentiated thyroid cancer ( 2.3 ) and for thyroid suppression test ( 2.4 ) When switching a patient to liothyronine sodium tablets, discontinue levothyroxine therapy and initiate liothyronine sodium tablets at a low dosage. Gradually increase the dose according to the patient's response ( 2.5 ) Adequacy of therapy determined with periodic monitoring of TSH and T3 levels as well as clinical status ( 2.6 ) 2.1 General Principles of Dosing The …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2024-03-15. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Patients with angina of effort or cardiovascular diseases and thyrotoxicosis
Established myocardial ischaemia (SPC 4.4 cross-refers to 4.3; levothyroxine with cautious dose escalation is recommended instead)

Side effects

Cardiac: anginal pain, cardiac arrhythmias, palpitations, tachycardia
Gastrointestinal: diarrhoea, vomiting
Nervous system: headache, tremor
Psychiatric: restlessness, excitability, insomnia
Musculoskeletal: muscle cramps, muscular weakness
General: fever, flushing, heat intolerance, sweating, excessive loss of weight (effects indicative of excessive dosage, usually resolving on dose reduction or withdrawal for a day or two)

Interactions

Bile acid sequestrants (colesevelam, cholestyramine, colestipol) and ion exchange resins (Kayexalate, sevelamer) decrease thyroid hormone absorption - give liothyronine at least 4 hours before these drugs or monitor TSH (US label 7.1; eMC 4.5 was not captured in the source bundle)
Biotin may interfere with thyroid immunoassays based on a biotin/streptavidin interaction, giving falsely decreased or increased results; risk increases with higher biotin doses - inform the laboratory (eMC 4.4)
Insulin and anti-diabetic drugs: liothyronine treatment may increase insulin or anti-diabetic drug requirements (eMC 4.4)

Clinical monograph

How it works

It is the active thyroid hormone (T3) and acts directly on nuclear thyroid receptors to regulate metabolism, bypassing the peripheral conversion of T4 to T3 required for levothyroxine.

Prescribing in practice

Use with caution in cardiac disease, as it can provoke angina or arrhythmia; introduce and titrate carefully under specialist supervision.
Its rapid onset and shorter half-life make dosing less stable than levothyroxine, so it is not routinely preferred for maintenance.
Initiation and ongoing use for hypothyroidism should usually be directed by a specialist (e.g. endocrinology).

Monitoring

Monitor clinical response and thyroid function; in those with cardiac disease watch for angina or palpitations during titration.

Counselling the patient

Report chest pain, palpitations or a fast or irregular heartbeat.
Do not change or stop the dose without specialist advice.

Evidence & guidelines

Specialist-initiated; not routinely recommended over levothyroxine for primary hypothyroidism (NICE NG145).

Reference: BTA/BTAC Guidelines on Hypothyroidism 2019; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Liothyronine sodium (T3) · Thyroid hormone (T3)

Pathways