Liothyronine (T3) is a thyroid hormone that may be prescribed for hypothyroidism and for people with absent or reduced thyroid function. It is a synthetic form of T3, the hormone normally produced by a healthy thyroid.
Liothyronine works by increasing the body’s metabolic rate and helping regulate cell development. It has a fast onset and a short duration of action.
In the US, levothyroxine (T4) is generally the standard treatment for hypothyroidism, and liothyronine is typically reserved for specific situations under an endocrinologist’s guidance. Liothyronine is available as tablets, and dosing is individualized based on symptoms and thyroid-related blood tests.
Indications for use
Liothyronine (T3) is indicated for the treatment of:
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Thyroid function deficiency;
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Primary thyroid atrophy;
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Partial or complete absence of the thyroid gland;
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Congenital hypothyroidism;
This medication is usually recommended when a more intensive treatment is required, as it acts quickly but its effects last only a short time.
Liothyronine should be used only as prescribed by a doctor, with individualized dosing. Regular medical follow-up is needed to assess the response to treatment.
Dosing instructions
Liothyronine should be taken by mouth with a glass of water, 30 minutes before or 2 hours after a meal. It is often taken in the morning to help prevent insomnia.
Adult dosage
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Mild hypothyroidism: The recommended starting dose is 25 mcg per day. A doctor may increase the dose by 25 mcg every 1 to 2 weeks. The maintenance dose is 25 mcg to 75 mcg per day;
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Myxedema: The recommended starting dose is 5 mcg per day. The doctor may increase the dose in increments of 5 mcg to 10 mcg per day every 1 to 2 weeks. Once the dose reaches 25 mcg per day, the doctor may increase it in increments of 5 mcg to 25 mcg every 1 to 2 weeks until the desired effect is achieved. The maintenance dose ranges from 50 mcg to 100 mcg per day.
Dosage for older adults or people with heart disease
For older adults or people with underlying cardiovascular disease, treatment is typically started at a lower dose, such as 5 mcg once daily, with gradual increases as directed by a clinician.
Dosage for congenital hypothyroidism in children
For congenital hypothyroidism in children, the starting dose is 5 mcg per day. The clinician may increase the dose in 5 mcg increments every 3 to 4 days until the desired response is reached.
Side effects
The most common side effects of liothyronine (T3) are headache, insomnia, weight loss, tremors, nervousness, irritability, muscle weakness, diarrhea, heat intolerance, excessive sweating, heart palpitations, muscle weakness, or cramps.
In women, liothyronine (T3) may also cause irregular menstrual cycles or bleeding outside the menstrual period.
Although less common, liothyronine (T3) may cause thyroid hormone toxicity, with symptoms such as chest pain, a fast or rapid heartbeat, nervousness, or sweating more than usual. In these cases, treatment should be stopped and emergency care should be sought immediately.
Contraindications for use
Liothyronine (T3) should not be used in people with uncorrected adrenal insufficiency.
This medication should not be used by anyone who is allergic to liothyronine or any component of the product.
People with underlying cardiovascular disease, diabetes, or osteoporosis may need closer monitoring and more cautious dose adjustment due to increased risks with thyroid hormone therapy, especially if overtreatment occurs.
Liothyronine (T3) is present in human milk. Breastfeeding decisions should weigh the benefits of breastfeeding, the parent’s need for thyroid hormone therapy, and any potential risks to the infant, with medical guidance.
Levothyroxine (T4) is the standard treatment for hypothyroidism during pregnancy. Liothyronine (T3) may be continued with close medical monitoring if already prescribed.
People with hypothyroidism who become pregnant or are trying to conceive should consult their clinician promptly. Pregnancy often increases thyroid hormone needs, requiring prompt dose adjustments and regular lab monitoring. Read more about thyroid tests.