What Is Cytomel?

Cytomel is the brand name for Liothyronine Sodium, a synthetic form of triiodothyronine (T3), one of the two main thyroid hormones produced by the thyroid gland. It is manufactured by Pfizer and is classified as a thyroid hormone replacement medication.

Cytomel is FDA-approved for:

• Replacement therapy in hypothyroidism — including primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) forms, whether congenital or acquired
• Adjunct to surgery and radioiodine therapy in the management of well-differentiated thyroid cancer (TSH suppression)
• Use as a diagnostic agent in thyroid suppression tests

Cytomel is also used off-label as an adjunct to Levothyroxine in patients with persistent hypothyroid symptoms, and as an augmentation strategy for treatment-resistant depression.

How does Cytomel work?

Cytomel contains Liothyronine (L-triiodothyronine or T3), which is the active form of thyroid hormone. Unlike Levothyroxine (T4), which must be converted to T3 in the body, Cytomel provides T3 directly. T3 binds to thyroid hormone receptors in cell nuclei throughout the body, where it increases basal metabolic rate, oxygen consumption, and the metabolism of carbohydrates, lipids, and proteins.

Because T3 is the active hormone, Cytomel acts more rapidly than T4-based medications like Synthroid, with effects beginning within hours rather than days. However, it also has a shorter duration of action, which is why some patients take it in divided doses throughout the day.

Cytomel should be taken on an empty stomach, 30 to 60 minutes before breakfast, for optimal absorption. Soy products, high-fiber foods, iron supplements, and calcium can all reduce absorption if taken at the same time.

What doses are available for Cytomel?

• 5 mcg tablet — commonly used as a starting dose, especially for elderly patients or those with heart conditions
• 25 mcg tablet — standard maintenance dose for many patients
• 50 mcg tablet — higher dose for patients requiring more thyroid hormone replacement

Generic Liothyronine is available in the same strengths (5 mcg, 25 mcg, and 50 mcg). Compounding pharmacies may also prepare custom strengths, including sustained-release formulations.

How hard is it to find Cytomel in stock?

Cytomel (Liothyronine) has a findability score of 65 out of 100, meaning it can be moderately difficult to locate at your pharmacy. Liothyronine has experienced intermittent supply disruptions due to limited generic manufacturers, increased demand from the ongoing levothyroxine shortage, and API sourcing challenges. While there is no formal FDA shortage listing as of early 2025, patients may struggle to find specific strengths or preferred manufacturers at certain pharmacies. Searching multiple pharmacies or using Medfinder can help you locate Cytomel or its generic equivalent in stock near you.

Who Can Prescribe Cytomel?

Cytomel can be prescribed by a range of healthcare providers, including:

• Endocrinologists — specialists in thyroid and hormonal disorders, most commonly prescribe Cytomel
• Internal Medicine physicians
• Family Medicine physicians
• Primary Care providers
• Integrative and Functional Medicine practitioners

Cytomel is also available through telehealth services, making it accessible for patients who may not have easy access to an endocrinologist in person.

Is Cytomel a controlled substance?

No, Cytomel is not a controlled substance. It does not have a DEA schedule designation and does not require special prescribing procedures. However, it is a prescription-only medication, meaning you will need a valid prescription from a licensed healthcare provider to obtain it.

It is important to note that the FDA has issued a boxed warning stating that thyroid hormones, including Cytomel, should not be used for weight loss. In euthyroid patients (those with normal thyroid function), therapeutic doses are ineffective for weight reduction, and larger doses can cause serious or life-threatening toxicity.

Common Side Effects of Cytomel

Most side effects of Cytomel are related to taking too much thyroid hormone. Common side effects include:

• Headache
• Irritability and nervousness
• Increased sweating and heat intolerance
• Tremor
• Diarrhea
• Menstrual changes
• Temporary hair loss (especially in children)
• Nausea

Serious side effects that require immediate medical attention include rapid or irregular heartbeat, chest pain, seizures, and signs of heart failure. Long-term overtreatment can lead to bone loss (osteoporosis). Patients with uncorrected adrenal insufficiency are at risk for adrenal crisis.

Alternative Medications to Cytomel

If you are unable to find Cytomel or generic Liothyronine, or if your doctor recommends a different option, several alternatives exist:

• Levothyroxine (Synthroid, Levoxyl, Tirosint) — synthetic T4 thyroid hormone and the most commonly prescribed thyroid replacement. The body converts T4 to T3 naturally. This is the first-line treatment for hypothyroidism.
• Armour Thyroid — desiccated (natural) thyroid extract from porcine thyroid glands containing both T4 and T3. Used by patients who prefer a natural option or do not respond well to synthetic T4 alone.
• NP Thyroid — another desiccated thyroid extract similar to Armour Thyroid, containing both T4 and T3 from porcine sources.
• Compounded Liothyronine — custom-compounded T3 preparations from compounding pharmacies, which may offer sustained-release formulations not available commercially.

Drug Interactions with Cytomel

Cytomel can interact with several commonly used medications:

• Warfarin (blood thinners) — Cytomel increases anticoagulant effects; INR monitoring is required
• Insulin and oral diabetes medications — thyroid hormones may increase blood glucose, requiring dose adjustments
• Digoxin — Cytomel may reduce digoxin levels in the blood
• Sympathomimetic amines — increased risk of heart problems when combined
• Cholestyramine and Colestipol — bind thyroid hormones in the gut, reducing absorption (take at least 4 hours apart)
• Iron supplements and calcium — reduce Cytomel absorption (take at least 4 hours apart)
• Estrogen and oral contraceptives — may alter thyroid hormone requirements
• Antidepressants (TCAs, SSRIs) — may enhance the effects of both medications

Final Thoughts on Cytomel

Cytomel (Liothyronine) is an important thyroid hormone replacement for patients who need direct T3 supplementation, whether due to hypothyroidism, thyroid cancer management, or as an adjunct to Levothyroxine therapy. While it has faced intermittent supply disruptions, generic Liothyronine remains available and is significantly more affordable than brand-name Cytomel.

If you are having trouble finding Cytomel or Liothyronine at your local pharmacy, Medfinder can help you locate pharmacies with stock near you. You can also ask your pharmacist about alternative manufacturers or check with compounding pharmacies for custom formulations. Pfizer RxPathways offers savings programs for eligible patients who need brand-name Cytomel.