Liothyronine (T3)
Synthetic T3 triiodothyronine (Cytomel). Specific indications (myxedema coma, T4-conversion impairment, MDD augmentation). NOT routine choice.
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WHAT IS LIOTHYRONINE (T3)?
Detailed overview
Liothyronine is the synthetic form of active T3 hormone (Cytomel, FDA 1956). NOT routine in hypothyroidism – levothyroxine (T4) provides physiologic T3 via endogenous deiodinase conversion. Specific indications: (1) MYXEDEMA COMA emergency treatment (fast-onset T3 IV), (2) subjective symptomatic hypothyroidism on levothyroxine with normal TSH (suspected T4-T3 conversion impairment, ETA 2012 PMID 24782999 debate), (3) MDD augmentation (Cooper-Kazaz 2007 PMID 17888912 treatment-resistant MDD), (4) DTC suppression post-thyroidectomy with fast onset. Short half-life (1 day vs T4 7 days), so 2-3x/day dosing required, harder to achieve stable levels.
ATC code
H03AA02
Prescription
Prescription only (Rx)
Mechanism
Synthetic T3 (triiodothyronine) hormone replacement, direct thyroid receptor agonist
Half-life
about 2.5 days (~60 h, shorter than T4)
Onset
within a few hours (max effect 2-3 days)
Data console
Lab data
Safety
Side effects, stop signs, contraindications
Side effects · 6
- Cardiovascular overstimulation: tachycardia, palpitations, atrial fibrillation and angina, especially in elderly or ischemic heart disease. The short half-life makes T3 peaks sharper than with T4.
- Overdose (iatrogenic hyperthyroidism) symptoms: tremor, sweating, heat intolerance, anxiety, insomnia, weight loss, diarrhea. The 2-3x/day dosing makes stable levels hard to maintain.
- Long-term over-replacement can cause reduced bone mineral density and osteoporosis, especially in postmenopausal women (under TSH suppression).
- Transient hair loss, headache, muscle cramps or fatigue at the start of treatment while thyroid status adjusts.
- Allergic/hypersensitivity reactions to tablet excipients (rash, urticaria); the hormone itself is rarely allergenic.
- May increase insulin or oral antidiabetic requirements and worsen glycemic control in diabetes.
Contraindications · 1
- Acute MI, untreated adrenal insufficiency, thyrotoxicosis
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Same therapeutic category
Studies
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Have a question about Liothyronine (T3)?
Educational drug info from official sources (PubMed, FDA, EMA). Does NOT replace medical consultation or the SmPC. Talk to your doctor!
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The information here is for educational and scientific purposes only. Medication use requires medical consultation and a prescription. The indications, dose ranges, and side effects listed here do NOT replace the official Summary of Product Characteristics (SmPC) or consultation with a physician. Do not start or stop any medication on your own. In an emergency, call your local emergency number.