How long does it take for Cytomel to work?

Once taken, Cytomel begins to work quickly to replace the T3 hormone, typically within a couple of hours.

Cytomel (Liothyronine) Oral: Uses, Side Effects, Dosages

Warning:

Thyroid hormones, such as Cytomel, are not indicated for the treatment of obesity or weight loss. Additionally, do not take more than the prescribed dose of your medication. Doses beyond the range of daily hormonal requirements can cause serious or life-threatening toxicity.

…

What Is Cytomel?

Cytomel (liothyronine) is a thyroid replacement medication, a synthetic form of a naturally occurring thyroid hormone called L-triiodothyronine, or T3. It can be used to treat hypothyroidism, a condition in which the thyroid gland makes too little hormone.

Cytomel replaces the hormone that the thyroid is no longer producing. This medication can also be used in higher doses to suppress thyroid function during treatment for thyroid cancer. Cytomel is an oral medication that comes in tablet form

Drug Facts

Generic Name: Liothyronine

Brand Name(s): Cytomel

Administration Route(s): Oral

Drug Availability: Prescription

Therapeutic Classification: Thyroid supplement

Available Generically: Yes

Controlled Substance: N/A

Active Ingredient: Liothyronine

Dosage Form(s): Tablet

What Is Cytomel Used For?

The Food and Drug Administration (FDA) approved Cytomel to treat hypothyroidism. In hypothyroidism, the thyroid is no longer functioning correctly and cannot make other hormones, such as T3 or T4, which are important hormones for many body functions. Cytomel can help replace the T3 hormone.

Cytomel can also be used with surgery and radioactive iodine treatment to treat thyroid cancer.

The FDA warns against using thyroid hormones, such as Cytomel, to treat obesity or for weight loss. Using too much of this medication can cause serious or life-threatening toxicity.

Cytomel (Liothyronine) Drug Information - Illustration by Zoe Hansen — Verywell / Zoe Hansen

How to Take Cytomel

Follow any specific instructions given by the healthcare provider who prescribed Cytomel.

You will typically take Cytomel once a day around the same time. You can take this medication with or without food.

Cytomel is usually prescribed as a long-term treatment, as this is a placement hormone for what the body is no longer producing.

Storage

Store Cytomel tablets at room temperature (between 59 degrees and 86 degrees Fahrenheit).

How Long Does Cytomel Take to Work?

Once taken, Cytomel is absorbed quickly and can start to work within a few hours. It can take a few days of taking the medication regularly for the drug levels in the body to reach a steady state.

What Are the Side Effects of Cytomel?

This is not a complete list of side effects and others may occur. A medical professional can advise you on side effects. If you experience other effects, contact your pharmacist or a medical professional. You may report side effects to the FDA at www.fda.gov/medwatch or 800-FDA-1088.

Common Side Effects

Cytomel’s side effects are usually related to the dose being higher than needed. The common side effects are similar to the signs of hyperthyroidism.

Side effects can include:

Headache
Nervousness
Irritability
Difficulty sleeping
Palpitations
Irregular heart rhythm
Shortness of breath
Muscle weakness
Increased appetite
Weight loss
Diarrhea
Intolerance to heat
Menstrual problems
Hair loss
Rash

Severe Side Effects

When taken at too high a dose, Cytomel can cause an irregular heart rhythm, chest pain, and myocardial infarction (lack of blood flow to your heart muscle). Also, if left untreated, and if you continue to take Cytomel at too high of a dose, any of the above listed side effects can become severe.

Call your healthcare team if you’re concerned you have serious side effects. Call 911 if you feel they are life-threatening or if you have a medical emergency.

Report Side Effects

Cytomel may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

(800) 332-1088

Dosage: How Much Cytomel Should I Take?

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

For oral dosage form (tablet):
- For hypothyroidism:
  - Adults—At first, 25 micrograms (mcg) once a day. Your doctor may adjust your dose as needed. However, the dose is usually not more than 75 mcg once a day.
  - Older adults—At first, 5 mcg once a day. Your doctor may adjust your dose as needed.
  - Children—At first, 5 mcg once a day. Your doctor may adjust your dose as needed.
- For thyroid cancer:
  - Adults and children—Use and dose must be determined by your doctor.
- For thyroid problem diagnosis:
  - Adults— 75 to 100 micrograms (mcg) once a day for 7 days. Your doctor will give you a radioactive iodine before and after the 7-day liothyronine.
  - Children—Use and dose must be determined by your doctor.

Modifications

If you are aged 65 years or older, your healthcare provider may decrease your dose to help reduce the risk of heart rhythm problems. Those who have other heart problems but are younger may require a smaller starting dose.

If you are pregnant while taking Cytomel, you may need a higher dose during your pregnancy.

Missed Dose

If you miss a dose, take it within the next few hours if you remember. Do not take the missed dose if it is almost time for your next dose. Do not double up on doses.

Try not to miss too many doses of Cytomel, as this can reduce the amount of thyroid replacement and may cause unwanted side effects.

Overdose: What Happens If I Take Too Much Cytomel?

Immediately notify your healthcare provider if you are concerned that you have taken too much Cytomel. Taking too much of this medication can cause serious side effects and potentially life-threatening problems due to toxicity.

Toxicity typically happens over time when too much of the drug is accumulated in the bloodstream. Therefore, symptoms may not appear right away.

If you notice any serious side effects, immediate medical evaluation may be necessary.

The signs that you are taking too much Cytomel are similar to the symptoms of hyperthyroidism. Confusion and disorientation can also occur.

What Happens If I Overdose on Cytomel?

If you think you or someone else may have overdosed on Cytomel, call a healthcare provider or the Poison Control Center (800-222-1222).

If someone collapses or isn't breathing after taking Cytomel, call 911 immediately.

911

Precautions

It is very important that your doctor check your or your child's progress at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it. Blood tests will be needed to check for unwanted effects.

Liothyronine should not be used for the treatment of obesity or for the purpose of losing weight. This medicine is ineffective for weight reduction and when taken in larger amounts, may cause more serious unwanted effects.

Call your doctor right away if you start to have chest pain, fast or irregular heartbeat, excessive sweating, difficulty with breathing, heat intolerance, nervousness, leg cramps, headache, irritability, sleeplessness, tremors, change in appetite, weight gain or loss, vomiting, diarrhea, fever, changes in menstrual periods, hives, or skin rash. These could be symptoms of too much medicine in your body.

This medicine may cause severe hypothyroidism, called myxedema coma, which may be life-threatening and requires immediate medical attention. Check with your doctor right away if you have the following symptoms: weakness, confusion or non-responsiveness, feeling cold, low body temperature, swelling of the body, especially the face, tongue, and lower legs, or difficulty breathing.

For patients with diabetes: It is very important that you keep track of your blood or urine sugar levels as instructed by your doctor. Check with your doctor right away if you notice any changes in your sugar levels.

If you think you have become pregnant while using this medicine, tell your doctor right away. You may need a larger dose of liothyronine while you are pregnant.

Women who are post-menopausal or who use this medicine for a long time may have some bone loss, which could lead to osteoporosis. Talk with your doctor if you have questions or concerns about this.

A temporary loss of hair may occur during the first few months of liothyronine treatment. Ask your doctor about this if you have any concerns.

Make sure any doctor or dentist who treats you knows that you or your child are using this medicine.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

What Are Reasons I Shouldn’t Take Cytomel?

Cytomel should not be taken when someone is experiencing myxedema coma, a condition in which severe hypothyroidism results in mental status changes and becomes potentially life-threatening.

People with adrenal insufficiency, a condition in which the adrenal glands aren’t producing enough hormones, should also not use Cytomel. If the adrenal insufficiency isn’t treated, taking Cytomel can cause more complications.

What Other Medications Interact With Cytomel?

Certain medications may need to be used cautiously or avoided altogether when taking Cytomel. These medications include:

Prevalite, Questran (cholestyramine)
Kayexalate, Kionex (sodium polystyrene)
Oral birth control pills with estrogen
Nolvadex, Soltamox (tamoxifen)
Glucocorticoids, a type of steroid medication
Phenobarbital
Rifadin, Rimactane (rifampin)
Cordarone, Pacerone (amiodarone)
Tricyclic antidepressants
Ketalar (ketamine)
Gleevec (imatinib)
Adrucil, Carac, Efudex, Fluoroplex (fluorouracil, also known as 5-FU)

What Medications Are Similar?

Levothyroxine is another thyroid replacement medication, although it is used to replace the T4 hormone. In this way, levothyroxine is different from Cytomel, which replaces T3. These medications are not typically used together, but have been used in combination in some clinical trials.

Levothyroxine is prescribed under several brand names, such as Synthroid and Levothroid. A generic version is also available.

Frequently Asked Questions

What is Cytomel used for?

Cytomel is used to replace the T3 hormone. This hormone is not produced enough in people with hypothyroidism (a low-functioning thyroid). It can also be combined with radioactive iodine to treat thyroid cancer.
How long does it take for Cytomel to work?

Once taken, Cytomel begins to work quickly to replace the T3 hormone, typically within a couple of hours.
What are the side effects of Cytomel?
Side effects from Cytomel are usually only due to the dose being too high. Those side effects can include:
- Headache
- Nervousness
- Weight loss
- Nausea
- Palpitations
- Diarrhea

How Can I Stay Healthy While Taking Cytomel?

Being prescribed a thyroid replacement medication means you will likely need to take if for the rest of your life. If you experience any side effects from the medication, let your healthcare team know quickly, as you may need a dosage adjustment.

Managing a lifelong condition like hypothyroidism can be difficult. Taking your medication correctly and following your healthcare provider’s guidance will help you get the full benefits. You can also implement lifestyle changes such as regular exercise and eating the right foods to help optimize your thyroid health.

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and is not intended as a replacement for medical advice, diagnosis, or treatment from a healthcare professional. Consult your healthcare provider before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

2 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.

Food and Drug Administration. Cytomel label.
Dayan C, Panicker V. Management of hypothyroidism with combination thyroxine (T4) and triiodothyronine (T3) hormone replacement in clinical practice: a review of suggested guidance. Thyroid Res. 2018;11:1.

By Julie Scott, MSN, ANP-BC, AOCNP
Julie is an Adult Nurse Practitioner with oncology certification and a healthcare freelance writer with an interest in educating patients and the healthcare community.

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Cytomel (Liothyronine) – Oral