Cytomel (Liothyronine)

Cytomel (liothyronine sodium) is a prescription medicine used to treat an underactive thyroid, also called hypothyroidism. It is a man-made form of T3, a hormone that helps control energy, body temperature, and metabolism. Cytomel may also be used with other treatments for certain thyroid cancers or thyroid testing. It comes as small tablets in 5 mcg, 25 mcg, and 50 mcg strengths.

Directions

Cytomel is taken by mouth once per day, usually in the morning. The right dose depends on a person’s condition, age, weight, heart health, other health problems, other medicines, and blood test results. Many adults with low thyroid levels start with about 25 mcg per day, while older adults or people with heart disease may start with around 5 mcg per day. Take Cytomel exactly as prescribed, and do not stop it or change the dose without talking to a healthcare provider.

Ingredients

The active ingredient in Cytomel is liothyronine sodium. The inactive ingredients may include calcium sulfate, corn starch, gelatin, stearic acid, sucrose, and talc.

Cautions

Before using this medication, you may want to consult a healthcare provider about the following:

• Any existing health conditions
• Any allergies
• A list of all medications currently being taken

Cytomel and other thyroid hormones should never be used for weight loss or to treat obesity. Higher doses may cause serious or life-threatening toxicity, especially when combined with stimulant-type appetite suppressants.

Talk to a healthcare provider before starting Cytomel if you have any heart problems such as coronary artery disease, heart failure, or a history of irregular heart rhythms. Too much thyroid hormone can speed up the heart, increase the risk of atrial fibrillation, and worsen angina.

Tell your provider if you have diabetes. Thyroid hormone can change how the body handles blood sugar, so insulin or other diabetes medications may need to be adjusted when Cytomel is started, changed, or stopped.

Let your provider know if you have any pituitary or adrenal problems. Untreated adrenal insufficiency needs to be corrected before Cytomel is started.

Long-term use of thyroid hormone in high doses can lower bone mineral density and increase the risk of osteoporosis, especially in postmenopausal women. The lowest effective dose should be used.

Cytomel can interact with many other medicines. Examples include warfarin and other blood thinners, certain antidepressants, oral diabetes drugs, insulin, estrogen products, and medications that affect thyroid hormone absorption such as iron, calcium, antacids, cholestyramine, sucralfate, and proton pump inhibitors. Always tell your provider about every prescription, over-the-counter, and herbal product you take.

Oral thyroid hormone products like Cytomel should not be used to treat myxedema coma, which is a medical emergency that requires intravenous treatment.

Thyroid hormone needs often change during pregnancy and may need to be increased. Tell your provider if you become pregnant, plan to become pregnant, or are breastfeeding while taking Cytomel.

Let your provider or dentist know you take Cytomel before any planned surgery or procedure.

Contraindications

Avoid taking or using this medication if you have uncorrected adrenal cortical insufficiency. Starting Cytomel before adrenal hormone replacement may trigger an acute adrenal crisis.

Side Effects

Common side effects of Cytomel are usually signs that the dose is too high. These can include:

• Fast or irregular heartbeat
• Chest pain or shortness of breath
• Headache
• Nervousness, irritability, or trouble sleeping
• Tremors or muscle weakness
• Increased appetite with unexplained weight loss
• Diarrhea or vomiting
• Feeling unusually hot, sweating more than usual
• Changes in menstrual periods
• Skin rash, itching, or hives
• Hair loss, especially during the first few months of treatment

Get medical help for any signs of a serious allergic reaction such as swelling of the face, lips, tongue, or throat, trouble breathing, or a severe rash.

Other serious problems can include a fast or irregular heartbeat, heart attack, severe chest pain, seizures, confusion, or symptoms of severe thyroid hormone toxicity.

Children on Cytomel should be watched closely, since too much thyroid hormone may affect bone growth.

References

• Cytomel Highlights of Prescribing Information. New York, NY: Pfizer Laboratories Div Pfizer Inc.; 2018.
• Cytomel Drug Label Information. New York, NY: Pfizer Laboratories Div Pfizer Inc.; 2025.