What Is Liothyronine? Uses, Dosage, and What You Need to Know in 2026

If you've been prescribed liothyronine — or you're curious about it as a treatment option — this guide covers everything you need to know: what it is, what it treats, how it works, how it's dosed, and what to expect. Written for patients in plain English.

What Is Liothyronine?

Liothyronine (pronounced lye-oh-THYE-roe-neen) is a synthetic form of triiodothyronine, more commonly known as T3 — one of the two main hormones produced by the thyroid gland. It is sold under the brand name Cytomel (oral tablets) and Triostat (intravenous solution for hospital use).

Liothyronine is chemically identical to the T3 hormone your thyroid gland naturally produces. When your thyroid doesn't make enough T3 — either due to an underactive thyroid, surgical removal of the thyroid, or other conditions — liothyronine replaces what's missing.

What Is Liothyronine Used For?

The FDA has approved liothyronine for three main uses:

Hypothyroidism (underactive thyroid): Used as replacement therapy when the thyroid gland doesn't produce enough hormone. This includes primary hypothyroidism (thyroid gland problem), secondary hypothyroidism (pituitary problem), and tertiary hypothyroidism (hypothalamus problem).

Thyroid cancer management (TSH suppression): Used as an adjunct to surgery and radioiodine therapy in well-differentiated thyroid cancer. Suppressing TSH prevents cancer regrowth.

Thyroid diagnostic testing: Used in the T3 suppression test to differentiate mild hyperthyroidism from thyroid gland autonomy.

Liothyronine is also used off-label as an adjunct to levothyroxine (T4) for patients who don't adequately convert T4 to T3, and in psychiatry as an augmentation strategy for treatment-resistant depression.

How Is Liothyronine Different from Levothyroxine?

Both are synthetic thyroid hormones, but they differ in important ways:

Liothyronine (T3): The active form. Works directly without needing to be converted. Faster onset of action (within hours). Shorter half-life (~2.5 days), so levels can fluctuate more between doses.

Levothyroxine (T4): A precursor hormone that the body converts to active T3 in peripheral tissues. Slower onset. Longer half-life (~7 days), providing more stable levels. First-line treatment for most hypothyroid patients.

Some patients — particularly those with certain genetic variants or poor T4-to-T3 conversion — may feel better with T3 included in their therapy regimen.

What Strengths Does Liothyronine Come In?

Liothyronine oral tablets come in three strengths:

5 mcg: Used for elderly patients, those with heart conditions, and children starting therapy at low doses.

25 mcg: The most common starting dose for adults with mild hypothyroidism.

50 mcg: Used for higher-dose maintenance therapy, particularly in thyroid cancer management.

What Is the Typical Liothyronine Dose?

Dosing depends on the condition being treated, your age, weight, and cardiac health. Typical adult dosing:

Mild hypothyroidism: Start at 25 mcg once daily; increase by up to 25 mcg every 1-2 weeks; usual maintenance is 25-75 mcg/day

Elderly or patients with heart disease: Start at 5 mcg/day; increase by 5 mcg every 2 weeks

Combination T4/T3 therapy: Typically a small dose of T3 (5-10 mcg/day) added to levothyroxine

How Should You Take Liothyronine?

Take liothyronine once daily, as directed by your prescriber.

It can be taken with or without food, though consistency matters — take it at the same time each day.

Take cholesterol-lowering medications (bile acid sequestrants like cholestyramine) at least 4 hours before or after liothyronine — they can reduce absorption.

Don't miss doses — if you miss a dose, take it as soon as you remember. If it's almost time for your next dose, skip the missed dose. Never double up.

Never stop taking liothyronine without talking to your doctor first.

Is Liothyronine a Controlled Substance?

No. Liothyronine is not a controlled substance and is not scheduled by the DEA. Any licensed prescriber can prescribe it, and it can be refilled without special restrictions.

The Bottom Line

Liothyronine is a synthetic T3 thyroid hormone that treats hypothyroidism, supports thyroid cancer management, and may help patients who don't convert T4 to T3 adequately. It comes in three strengths and is taken once daily. For more detail on how it actually works in the body, see our deep-dive on how liothyronine works. If you need help finding liothyronine in stock near you, use medfinder.