Liothyronine (T3) (Liothyronine Sodium (L-Triiodothyronine, T3))
Also sold as: Cytomel, Tertroxin, Thybon, Liothyronine Sodium Injection
Pregnancy
Cat A
Lactation
Safe
Schedule
H
Forms
Tablet 5mcg +3
Indications
- Hypothyroidism (when T4-to-T3 conversion is impaired)
- Myxedema coma (IV liothyronine ± IV levothyroxine)
- Thyroid cancer management (T3 used to withdraw patients from levothyroxine before radioiodine scan/therapy)
- Diagnostic thyroid suppression testing
- Refractory depression (adjunct to antidepressants — off-label)
- Goitre suppression (selected cases)
Adult Dosing
Hypothyroidism (oral)
Start 5mcg once daily; increase by 5mcg every 1–2 weeks
Once to three times daily (T3 half-life 1–2 days; often requires BD or TDS dosing for stability)
Typical maintenance 25–75mcg/day in divided doses. Not used as sole thyroid replacement routinely — combination T4+T3 or T4 alone preferred. Monitor free T3, T4, and TSH.
Thyroid cancer — levothyroxine withdrawal before radioiodine
Convert from levothyroxine to liothyronine 25mcg BD for 4–6 weeks, then stop 10–14 days before radioiodine
Transition period before radioiodine scan; patients remain hypothyroid for shorter time due to shorter T3 half-life
Reduces duration of severe hypothyroid symptoms vs direct T4 withdrawal. recombinant TSH (rhTSH) injection is now preferred alternative.
Myxedema coma (IV)
5–20mcg IV every 4–8 hours until patient can take oral medication
Combined with IV levothyroxine 100–200mcg loading dose; supplemented with IV T3
ICU setting only. Give IV hydrocortisone 100mg every 8h FIRST (adrenal insufficiency may coexist). Monitor cardiac rate and rhythm closely.
Refractory depression (adjunct — off-label)
25mcg once daily (morning)
Added to antidepressant after partial response; trial 4–8 weeks
Evidence base exists primarily with tricyclic antidepressants (imipramine). Endocrinologist input recommended.
Pediatric Dosing
Rarely used as primary thyroid replacement in children. Specialist endocrinologist guidance essential. Monitor growth and development.
Renal Dose Adjustment
| CrCl / eGFR | Dose Adjustment |
|---|---|
| Any degree of renal impairment | No specific dose adjustment; titrate by TSH and free T3 levels |
Hepatic Adjustment
Use with caution in severe hepatic disease. Liothyronine binding proteins are hepatically synthesised — free T3 levels may be elevated. Start at lowest dose and monitor carefully.
Pregnancy & Lactation
Pregnancy: Category A
Thyroid hormones are essential for fetal development. Liothyronine is pregnancy category A. However, T3 crosses the placenta poorly (less than T4). Levothyroxine (T4) is preferred in pregnancy as it is converted to T3 locally in fetal tissues. Liothyronine is rarely used as primary replacement in pregnancy — use levothyroxine instead.
Lactation: Safe
T3 is naturally present in breast milk. Exogenous liothyronine at replacement doses does not significantly increase breast milk T3 levels. Compatible with breastfeeding.
Top Drug Interactions
| Interacting Drug | Effect | Severity |
|---|---|---|
| Warfarin / Coumarins | Liothyronine (especially at higher doses) increases vitamin K clotting factor catabolism, enhancing anticoagulant effect. Monitor INR closely, especially when starting or adjusting T3. | Major |
| Sympathomimetics / adrenergic agents (including beta-agonists) | T3 increases adrenergic receptor sensitivity. Concurrent use increases risk of coronary artery spasm and cardiac adverse effects. | Moderate |
| Tricyclic antidepressants (imipramine, amitriptyline) | Mutual enhancement; T3 accelerates onset of TCA antidepressant effect and increases risk of cardiac arrhythmia in susceptible patients | Moderate |
| Antidiabetic agents (insulin, metformin, sulphonylureas) | Thyroid hormones increase insulin requirements; initiation or dose increase of T3 may worsen glycaemic control in diabetics | Moderate |
| Calcium carbonate / Iron supplements / Cholestyramine | Reduce oral T3 absorption — similar to T4. Separate by at least 4 hours. | Moderate |
| Digoxin | Hypothyroid patients are sensitive to digoxin toxicity; T3 replacement normalises volume of distribution, potentially reducing digoxin levels. Monitor digoxin concentration. | Moderate |
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Side Effects
Common
- All symptoms are those of over-replacement (hyperthyroidism):
- Palpitations and tachycardia
- Tremor
- Heat intolerance
- Sweating
- Anxiety and irritability
- Insomnia
- Diarrhoea
- Weight loss
Serious / Discontinue If
- Atrial fibrillation (particularly in elderly on high doses)
- Angina pectoris / Myocardial infarction (if initiated too rapidly in cardiac patients)
- Heart failure exacerbation
- Osteoporosis with long-term supratherapeutic dosing
- Thyrotoxic crisis (with gross overdose)
Contraindications
- Uncorrected adrenal insufficiency (must treat adrenal before thyroid)
- Thyrotoxicosis
- Acute myocardial infarction (relative — do not initiate or increase dose)
- Hypersensitivity to any component
Available Indian Brands
| Brand | Manufacturer | Price (approx) |
|---|---|---|
| Cytomel 25mcg | Pfizer India | 30 tab ₹185 |
| Tertroxin 20mcg | GlaxoSmithKline India | 30 tab ₹160 |
| Thybon 25mcg | Abbott India | 30 tab ₹175 |
| Liothyronine 5mcg | Sun Pharmaceutical | 30 tab ₹125 |
Monitoring Required
- Free T3 (primary monitoring parameter for liothyronine therapy)
- Free T4 and TSH (for overall thyroid status)
- Heart rate and cardiac rhythm (ECG in elderly or cardiac patients)
- Bone mineral density with long-term use (osteoporosis risk)
- Blood glucose in diabetics (T3 affects insulin sensitivity)
- INR in anticoagulated patients
- Clinical symptoms: energy, weight, mood, temperature tolerance
Patient Counseling Points
- T3 (liothyronine) works much faster than T4 tablets — effects are felt within hours to days, not weeks.
- Because it is fast-acting, symptoms of too-high a dose (fast heart rate, tremor, sweating) may develop quickly — report these promptly.
- Take the tablet at the same time(s) each day — consistency is important for stable hormone levels.
- Keep calcium tablets, iron, and antacids at least 4 hours away from your liothyronine dose.
- Do not stop abruptly — hypothyroidism symptoms return rapidly due to short half-life.
- Have regular thyroid blood tests — the free T3 level is specifically monitored on this medicine.
- If you have heart disease, dose increases should be made very slowly under close supervision.
- Tell your doctor about all other medications — several drugs interact with thyroid hormones.
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Clinically reviewed by: Dr. Sanjay Kalra, DM (Endocrinology), Bharti Hospital Karnal
Last reviewed: 2026-03-20
References
- FDA Prescribing Information: Cytomel (liothyronine sodium). Pfizer Inc.
- Jonklaas J et al. Guidelines for the Treatment of Hypothyroidism. Thyroid. 2014;24(12):1670–1751.
- Indian Pharmacopoeia Commission. Liothyronine Sodium monograph. IP 2022.
- CIMS India Drug Database 2025 — Liothyronine
- Wiersinga WM et al. 2012 ETA Guidelines: The Use of L-T4 + L-T3 in the Treatment of Hypothyroidism. Eur Thyroid J. 2012;1(1):55–71.