Cytomel: Uses, Side Effects, Interactions, and More


If you've been diagnosed with hypothyroidism , you will almost certainly be prescribed the drug levothyroxine (sold under the trade names Synthroid, Levoxyl, and others), a synthetic hormone that replenishes the production of the thyroid hormone thyroxine, also known as T4. But if you're taking levothyroxine and you're still feeling sick, another drug known as cytomel (liothyronine) can help.

Cytomel is a synthetic form of the triiodothyronine hormone known as T3, which is equally important for a healthy metabolism. Some endocrinologists also recommend the use of natural dehydrated thyroid (NDT), a preparation derived from the dry glands of pigs or cows that has T3 and T4 along with another thyroid protein such as thyroglobulin.

Get Medical Information / Laura Porter

T4 vs T3

Thyroxine (T4) and triiodothyronine (T3) are the two main hormones produced by the thyroid gland . Its function is to regulate metabolism (convert oxygen and calories into energy). T3 is considered the active form of thyroid hormone. It is formed from T4, the "storage hormone," in a process known as monodeiodination , in which T4 loses an iodine atom to become T3.

This means that if you don't have enough T4, your body can't make enough T3. T4 supplementation through levothyroxine increases its levels and ensures adequate T3 production. For many people with hypothyroidism, this is enough to bring thyroid hormone levels back into the ideal range. However, for some people, standard therapy is not enough to relieve symptoms.

Cytomel vs Synthroid

While T3 medications like Cytomel may seem like an ideal choice for hormone replacement therapy, T3 is rapidly absorbed from the gut and can accumulate quickly, leading to symptoms of hyperthyroidism (an overactive thyroid gland).

After this explosion, the level drops rapidly, along with your body's ability to create T4. Because of this, you have to take Cytomel several times a day, but even that doesn't match your T3 levels in an ideal way.

In contrast, T4 medications such as levothyroxine are absorbed more gradually and can maintain a constant blood level, providing the body with all the T4 it needs to synthesize T3.

Another problem is that T3 medications can interfere with T4 blood tests that are used to monitor the effectiveness of hormone replacement therapy. For these reasons, many healthcare providers consider that T3 medications are not necessary.

Furthermore, T4 and T3 therapy makes it difficult to maintain a normal T4: T3 ratio, which ranges from 13: 1 to 16: 1. In fact, several clinical trials have compared T4 alone with T4 plus T3 and found that La combination also promotes mild hyperthyroidism.

Cytomel Pros
Cons of Cytomel

  • Rapid absorption means inconsistent levels

  • I need to take more often

  • May affect thyroid blood tests

  • It can cause symptoms of hyperthyroidism.

Current American Thyroid Association guidelines recommend treating people with hypothyroidism with only T4 first. T3 supplementation should be considered in people who continue to have symptoms of hypothyroidism and whose T3 levels remain in the lower end of the normal range.

Natural desiccated thyroid gland

Several healthcare providers have been successful in treating thyroid patients with a naturally desiccated thyroid gland , also known as a noninvasive test. NK is obtained from the dried (dehydrated) thyroid gland of pigs or cows and provides T3, T4, and other thyroid hormones found in the human thyroid gland. NK is sold in the United States under a variety of brand names, including:

  • Thyroid armor
  • Nature-Troid
  • Thyroid WP

Cytomel uses

Cytomel was first approved by the Food and Drug Administration (FDA) in 1956. and the injectable form of the drug is marketed as Triostat. In addition to hypothyroidism, Cytomel is used to:

  • Pituitary Thyroid Stimulating Hormone Suppression – This can be a valuable add-on treatment for people with thyroid cancer who are receiving radioactive iodine therapy.
  • Thyroid Suppression Test : Cytomel is prescribed as part of this test to help diagnose the cause of hyperthyroidism.
  • Goiter – an abnormally enlarged thyroid gland; goiter is often caused by a thyroid disorder.
  • Myxedema – A symptom of severe hypothyroidism, myxedema includes rough skin and hair, an enlarged tongue, a hoarse voice, and swelling of the face or entire body.
  • Myxedematous coma : An extreme and life-threatening complication of hypothyroidism, myxedematous coma causes a decrease in body temperature and blood pressure and loss of consciousness.

Cytomel debate

The endocrinology community continues to debate the use of T3 to treat hypothyroidism. Despite opposition from many physicians, more and more research is shedding light on the correct use of T3 medications in people with hypothyroidism. From them:

  • A study published in 2017 found a genetic defect that prevents T4 from turning into T3. People with this defect respond poorly to levothyroxine treatment alone.
  • A 2020 review of the evidence cited research showing that T3 can lower cholesterol, reduce body weight, and offer better resolution of hypothyroid symptoms than levothyroxine alone.
  • A 2021 review of the quality of life of people treated for hypothyroidism provides evidence that levothyroxine plus T3 improves quality of life and depression more than levothyroxine alone. Among the participants, 49% preferred the combination treatment, while only 15% preferred levothyroxine alone.

Side effects

Except for the appearance of hyperthyroid symptoms, Cytomel side effects are rare and generally mild. Symptoms of hyperthyroidism include:

  • Irritability or restlessness
  • Fatigue
  • Soft spot
  • Easily overheats
  • Insomnia
  • Tremors, usually in your hands.
  • Frequent bowel movements
  • Humor changes
  • Preserve

Other possible side effects include:

  • Involuntary weight loss
  • Nervousness
  • Excessive sweating
  • At the start of therapy, temporary hair loss.

If any of these side effects become severe or do not go away over time, tell your doctor. Less common side effects that can be serious and require immediate medical attention include:

  • Chest pain
  • Fast or irregular heartbeat

When taking any medication, it is important that you and your doctor consider the possible risks and possible benefits.

Do not take these medications together

Antacids and cholesterol-lowering medications Colestid (Colestipol) and Questran (Cholestyramine) can interfere with the absorption of Cytomel. To avoid this, always separate doses of Cytomel and other medications by at least four hours.


Cytomel is known to interact with some common medications. From them:

  • Coumadin (warfarin) and other anticoagulants (blood thinners) : Cytomel and other thyroid hormone medications can increase blood clotting, so the dose of blood thinner may need to be adjusted to compensate for this effect.
  • Insulin and other diabetes medicines : Cytomel can raise blood insulin levels, so your blood sugar needs to be checked regularly and your dose may need to be adjusted.
  • Estrogen-based contraceptives, such as birth control pills : Medications that contain estrogen can reduce the amount of active cytomel in the blood. You may need a higher dose of Cytomel if you are taking estrogen-based birth control.
  • Tricyclic antidepressants : Cytomel can potentially increase the side effects of tricyclic medications and their combination can cause arrhythmias (abnormal heartbeats). The dose of the tricyclic drug or another drug may need to be changed.


Cytomel should not be used by people with:

  • Untreated adrenal insufficiency (when the adrenal glands do not make enough of the hormone cortisol)
  • Thyrotoxicosis (elevated levels of thyroid hormones for any reason)

Cytomel is not absorbed into fetal tissues and is therefore considered safe during pregnancy. Although liothyronine can pass through breast milk, the amount excreted is so small that it can be considered harmless.

How is it written

Cytomel is available in 5, 25, and 50 mcg dosages. The recommended dose depends on the condition being treated and the level of thyroid dysfunction.

For hypothyroidism that has not responded adequately to levothyroxine alone, your healthcare provider will likely prescribe 5 mcg of T3 once a day and increase it every week or two until tests show that your thyroid hormones are in the low range. desired levels. …

The starting dose should be lower (5 mcg per day) in:

  • Children and adolescents
  • People over 65
  • People with cardiovascular disease or other debilitating medical conditions.

Correct dosing of Cytomel is relatively difficult and you should aim to maintain a normal T4 to T3 ratio of around 16: 1. Ideally, combination therapy should be carried out by an endocrinologist.

Frequently asked questions

How long does Cytomel stay in your system?

Cytomel is quickly absorbed into your system. Within four hours of taking it, 95% of the drug is eliminated from your digestive system. The biological half-life is 2.5 days.

How long does it take for Cytomel to start working?

Cytomel is at its peak in your body within two to three days after you start taking it, which means you will notice a difference in your symptoms very soon.

Get the word of drug information

If you don't feel as well as you should, even if your thyroid test results are within the normal range, talk to your doctor. While you may be interested in trying T3, be aware that some healthcare providers may recommend that you stick with levothyroxine alone, as this is the standard of care for hypothyroidism according to the guidelines set forth by the American Association of Endocrinologists. Clinicians (AACE). and the American Thyroid Association (ATA).

However, given Cytomel's promising new research for some people with hypothyroidism, your healthcare provider may be open to discussing the potential benefits.

Thyroid Discussion Guide

Get our printable guide to your next doctor's appointment to help you ask the right questions.

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