How is Cytomel Used and Is It Better Than Synthroid

What place does it have in thyroid disease treatment?

If you been diagnosed with hypothyroidism, it's virtually certain that you've been prescribed the drug levothyroxine (marketed under the brand names Synthroid, Levoxyl, and others)—a synthetic hormone that replenishes the thyroid hormone thyroxine, also known as T4. But if you are on levothyroxine and still not feeling well, another drug known as Cytomel (liothyronine) may help.

Cytomel is the synthetic form of the hormone triiodothyronine, known as T3, which is equally important to healthy metabolic function. Some endocrinologists also endorse the use of natural desiccated thyroid (NDT), a drug derived from dried glands of pigs or cows that has T3 and T4 along with other thyroid gland protein such as thyroglobulin.

all about treating hypothyroidism with cytomel (t3)

Verywell / Laura Porter

T4 vs. T3

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

That means if you don't have enough T4, your body can't make enough T3. Adding T4 through levothyroxine increases your levels and enables adequate production of T3. For many people with hypothyroidism, this is enough to get their thyroid hormone levels back in the ideal range. However, for some people, the standard therapy isn't enough to get rid of their symptoms.

Cytomel vs Synthroid

While T3 drugs like Cytomel may seem the ideal choice for hormone replacement therapy, T3 is rapidly absorbed in the intestines and can build up quickly, leading to symptoms of hyperthyroidism (overactive thyroid).

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

By contrast, T4 drugs like levothyroxine are absorbed more gradually and can maintain a consistent level in the blood, providing the body with all the T4 it needs to synthesize T3.

Another concern is that T3 drugs can affect the T4 blood tests used to monitor the effectiveness of hormone replacement therapy. For these reasons, many healthcare providers consider T3 drugs unnecessary.

Plus, therapy with both T4 and T3 makes it difficult to maintain a normal T4-to-T3 ratio, which is between 13:1 and 16:1. In fact, several clinical trials have compared T4 alone to T4 plus T3 and found that the combination also contributes to mild hyperthyroidism.

Cytomel Pros
  • Directly replaces T3

  • Can improve symptoms better than T4 alone in some people

Cytomel Cons
  • Quick absorption means inconsistent levels

  • Must be taken more often

  • Can interfere with thyroid blood tests

  • Can cause symptoms of hyperthyroidism

Current guidelines from the American Thyroid Association recommend that people with hypothyroidism be treated initially with T4 alone. Adding T3 should be considered in people who continue to have symptoms of hypothyroidism, and whose T3 levels remain in the low end of the normal range.

Natural Desiccated Thyroid

Some healthcare providers have found success in treating their thyroid patients with natural desiccated thyroid, also known as NDT. NDT is derived from the dried (desiccated) thyroid glands of pigs or cows and provides T3, T4, and other thyroid hormones found in the human thyroid gland. NDT is marketed under various brand names in the United States, including:

  • Armour Thyroid
  • Nature-Throid
  • WP Thyroid

Cytomel Uses

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

  • Pituitary thyrotropin suppression: This can be a valuable additional treatment for people with thyroid cancer who are undergoing radioiodine therapy.
  • Thyroid suppression test: Cytomel is given as part of this test to help diagnose the cause of hyperthyroidism.
  • Goiter: An abnormally enlarged thyroid gland, goiters are often caused by thyroid disease.
  • Myxedema: A symptom of severe hypothyroidism, myxedema involves coarse skin and hair, an enlarged tongue, a hoarse voice, and puffiness in the face or throughout the body.
  • Myxedema coma: An extreme, life-threatening complication of hypothyroidism, a myxedema coma causes a drop in body temperature and blood pressure along with a loss of consciousness.

Debate Over Cytomel

The endocrinology community continues to debate the use of T3 for treating hypothyroidism. Despite resistance from many medical practitioners, a growing body of research is shedding light on the appropriate use of T3 drugs in people with hypothyroidism. Among them:

  • Research published in 2017 identified a genetic defect that interferes with the conversion of T4 into T3. People with this defect don't respond well to levothyroxine treatment alone.
  • A 2020 review of evidence cited a study showing that T3 can lower cholesterol levels, reduce body weight, and offer a better resolution of hypothyroid symptoms than levothyroxine alone.
  • A 2021 review focusing on quality of life among people treated for hypothyroidism cited evidence that levothyroxine plus T3 improved quality of life and depression scores more than levothyroxine alone. Among participants, 49% preferred the combination treatment while only 15% preferred levothyroxine alone.

Side Effects

With the exception of triggering hyperthyroid symptoms, side effects from Cytomel are rare and generally mild. Symptoms of hyperthyroidism include:

  • Irritability or anxiety
  • Fatigue
  • Weakness
  • Becoming easily overheated
  • Insomnia
  • Tremor, usually in your hands
  • Frequent bowel movements
  • Mood swings
  • Goiter

Other possible side effects include:

  • Unintended weight loss
  • Nervousness
  • Excessive sweating
  • Early in therapy, temporary hair loss

If any of these side effects become severe or don't go away over time, let your healthcare provider know. Less common side effects that can be serious and require immediate medical attention include:

  • Chest pain
  • Rapid or irregular heartbeat

With any medication, it's important for you and your healthcare provider to consider the potential risks along with the possible benefits.

Don't Take These Drugs Together

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


Cytomel is known to interact with certain common medications. Among them:

  • Coumadin (warfarin) and other anticoagulants (blood thinners): Cytomel and other thyroid hormone drugs can enhance blood clotting, so you may need an adjustment of your blood thinner dosage to compensate for this effect.
  • Insulin and other diabetes drugs: Cytomel can increase blood insulin levels, so your blood sugars should be routinely monitored and you may need a dose adjustment.
  • Estrogen-based contraception such as birth control pills: Estrogen-containing drugs may reduce the amount of active Cytomel in your blood. You may need a higher dose of Cytomel if you're on estrogen-based birth control.
  • Tricyclic antidepressants: Cytomel can potentially increase the side effects of tricyclic drugs and the combination can trigger bouts of arrhythmia (abnormal heartbeats). A change in tricyclic dose or a different medication may be necessary.


Cytomel should not be used in people with:

  • Untreated adrenal insufficiency (when the adrenal glands don't produce enough of the hormone cortisol)
  • Thyrotoxicosis (excessive thyroid hormone levels from any cause)

Cytomel is not absorbed in fetal tissue and is therefore considered safe during pregnancy. While liothyronine can be passed through breastmilk, the amount secreted is so small as to be considered harmless.

How It's Prescribed

Cytomel is available in 5-microgram (mcg), 25-mcg, and 50 mcg doses. The recommended dosage depends on the condition being treated and the level of thyroid gland dysfunction.

For hypothyroidism that hasn't responded adequately to levothyroxine alone, your healthcare provider will likely start you on a once-a-day 5-mcg dose of T3 and increase it every week or two until tests show your thyroid hormones are in the desired range.

The starting dosage should be lower—5 mcg per day—in:

  • Children and adolescents
  • People over age 65
  • People with cardiovascular disease or other debilitating illnesses

Proper dosing of Cytomel is relatively difficult and should aim to maintain the normal T4 to T3 ratio of about 16:1. Combination therapy should ideally be managed by an endocrinologist.

Frequently Asked Questions

How long does Cytomel stay in your system?

Cytomel quickly absorbs into your system. Within four hours after you take it, 95% of the drug is gone from your digestive system. The biological half-life is 2.5 days.

How long does it take for Cytomel to start working?

Cytomel reaches its maximum activity in your body within two to three days after you start taking it, meaning you should notice a difference in your symptoms quite soon.

A Word From Verywell

If you don't feel as well as you think you should, even if your thyroid test results fall within the normal range, speak with your healthcare provider. While you may be interested in trying a T3 drug, know that some healthcare providers may recommend that you stick with levothyroxine alone, given that it is the standard of care for hypothyroidism per guidelines set forth by the American Association of Clinical Endocrinologist (AACE) and American Thyroid Association (ATA).

However, given the newer, promising research into Cytomel for some people with hypothyroidism, your healthcare provider may be open to a discussion about the possible benefits.

Thyroid Disease Doctor Discussion Guide

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14 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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