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Liothyronine (T3) is a synthetic thyroid hormone that compounding pharmacies prepare as oral capsules, including slow-release forms, in strengths not manufactured, by prescription.
Liothyronine is the synthetic form of triiodothyronine (T3), the more active of the two thyroid hormones. In the body most T3 comes from conversion of thyroxine (T4) in peripheral tissues; T3 enters the cell nucleus, binds thyroid hormone receptors and switches on gene transcription that sets metabolic rate, heart rate and growth. The manufactured products are Cytomel (liothyronine sodium tablets, Pfizer) and generics, FDA-approved for replacement therapy in primary, secondary and tertiary hypothyroidism, as an adjunct to surgery and radioiodine for TSH suppression in well-differentiated thyroid cancer, and as a diagnostic agent in thyroid suppression tests; an injection also exists. The tablets come in a few fixed strengths and release the whole dose at once, so a prescriber might order compounded liothyronine in a fractional strength, as a slow-release capsule, or free of a specific excipient. Compounded preparations are not FDA-approved and require a prescription.
Liothyronine carries the FDA boxed warning shared by all thyroid hormones: it must not be used for obesity or weight loss, because doses beyond the body's hormonal requirement can cause serious or life-threatening toxicity, especially with sympathomimetic amines such as amphetamines. Do not use it with uncorrected adrenal insufficiency, which must be treated first. Too much thyroid hormone strains the heart, causing palpitations, fast or irregular heartbeat, angina and, in older adults or people with heart disease, heart attack; over-replacement also thins bone and can worsen diabetes control. It increases the effect of warfarin and reduces the effect of digoxin. Bile acid binders such as cholestyramine block its absorption and should be taken at least four hours apart; estrogens, androgens, phenytoin, carbamazepine, rifampin, amiodarone, high-dose propranolol, antidepressants and ketamine can change its levels or effects. Requirements rise in pregnancy and treatment should not be stopped; the label says liothyronine is present in milk with too little information on infant effects, and Drugs.com's breastfeeding monograph, citing primary studies, notes T3 is a normal milk component. Signs of excess are weight loss, nervousness, sweating, heat intolerance, tremor, insomnia and hair loss. Call your prescriber for chest pain or a racing or irregular pulse. If side effects bother you, talk to your prescriber or pharmacist.
Liothyronine is synthetic T3; thyroid hormones act through nuclear receptor binding and regulation of DNA transcription and protein synthesis. About 95 percent of an oral dose is absorbed within 4 hours; T3 is less firmly protein bound than T4, which explains its lower serum levels and shorter half-life of about 2.5 days; onset is within hours with maximal response in 2 to 3 days. Immediate-release dosing produces a sharp serum T3 peak at about 2 to 4 hours that can exceed the reference range and perturb TSH, unlike the flat physiologic profile (Dayan and Panicker, Thyroid Research 2018). Labeled indications (Cytomel): hypothyroidism, TSH suppression in well-differentiated thyroid cancer, thyroid suppression testing; not indicated for myxedema coma. Prescribers have ordered compounded liothyronine, including slow-release capsules, for patients with persistent symptoms on levothyroxine alone as part of a supervised T4 plus T3 trial; the 2018 review reports that meta-analyses of randomized trials found no population-level benefit of combination therapy, that the ATA does not recommend compounded T3 except for documented allergy to commercial products and cites thyrotoxicosis and hypothyroidism from compounding errors, and that no commercial sustained-release T3 exists. Dosing, strength and titration are per prescriber, starting low in the elderly and in cardiovascular disease. Monitor TSH after initiation and dose change and every 6 to 12 months once stable, total T3 where TSH is unreliable, growth in children, INR with anticoagulants, and bone density in postmenopausal women. Not a controlled substance.
Compounded at Bayview
Patient guides for the preparations we make most often. Each one is compounded to order and requires a prescription.
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Every preparation in our formulary that contains this ingredient. Strength, base and dose form are set by the prescription.
Other salt forms of this molecule, and ingredients commonly compounded alongside it.
This page describes an active pharmaceutical ingredient, not a finished drug product. Bayview Pharmacy compounds preparations containing it only on a prescriber's order for an individual patient.
Compounded preparations are not FDA-approved, and the FDA has not evaluated them for safety, effectiveness, or manufacturing quality. Nothing on this page is a claim that any preparation is effective for any condition.
A valid prescription is required. Availability depends on Bayview's licensure in your state. This page is general information, not medical advice. Discuss your situation with a licensed healthcare provider.
Our pharmacists work with prescribers to build preparations around a patient's dose, form and tolerances. Ask us what is possible with this ingredient.
