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.
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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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Educational drug info from official sources (PubMed, FDA, EMA). Does NOT replace medical consultation or the SmPC. Talk to your doctor!
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.