Liothyronine, also known as T3, is a synthetic form of the thyroid hormone triiodothyronine. It is primarily used as a replacement hormone therapy for individuals with low thyroid hormone levels (hypothyroidism) or after thyroid cancer treatment. This article provides a comprehensive overview of liothyronine, including its uses, mechanism of action, potential side effects, and important considerations before taking it.
Overview of Liothyronine
Liothyronine is a potent thyroid hormone that plays a crucial role in regulating metabolism, energy levels, and overall bodily functions. While T4 (thyroxine) is often considered the storage form of thyroid hormone, T3 is the active form that the body directly utilizes. In some individuals, the conversion of T4 to T3 may be inefficient, necessitating T3 supplementation.
What is Liothyronine Used For?
Liothyronine is commonly prescribed for the following conditions:
- Hypothyroidism: To restore adequate thyroid hormone levels in individuals whose thyroid gland does not produce enough.
- Thyroid Cancer: To suppress thyroid-stimulating hormone (TSH) levels, which can help prevent the growth of thyroid cancer cells. Liothyronine tells the thyroid gland to stop producing its own hormones, which can help stop the growth of thyroid cancer.
- Diagnostic Purposes: To test for thyroid problems, as determined by a healthcare provider.
Liothyronine may also be used for other conditions as determined by a healthcare provider.
How Does Liothyronine Work?
Liothyronine (T3) provides a direct source of the active thyroid hormone, compensating for insufficient production by the thyroid gland. In the context of thyroid cancer, liothyronine helps suppress TSH, which can stimulate the growth of cancerous thyroid cells.
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Dosage Forms and Storage
Liothyronine is available in oral tablet form, with strengths of 5 mcg, 25 mcg, and 50 mcg. Brand names include Cytomel.
Liothyronine should be stored at room temperature, between 59°F and 86°F (15°C and 30°C).
Common and Serious Side Effects of Liothyronine
Common Side Effects
The most common side effects of liothyronine include:
- Arrhythmias (abnormal heart rhythms)
- Heart attack
- Shortness of breath
- Headache
- Nervousness
- Crankiness
- Trouble sleeping
- Tremors
- Muscle weakness
- Increased appetite
- Weight loss
- Diarrhea
- Trouble tolerating heat
- Menstrual changes
- Rash
If any of these side effects bother you, inform your healthcare provider.
Serious Side Effects
While less common, the following serious side effects require immediate medical attention:
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- Severe Allergic Reactions: Symptoms include breathing problems, wheezing, racing heart, fever, swollen lymph nodes, swelling of the face, lips, mouth, tongue, or throat, trouble swallowing, itching, skin rash, hives, nausea, vomiting, dizziness, feeling lightheaded, fainting, stomach cramps, and joint pain.
- Heart Problems: Increased heart rate, abnormal heartbeat, and chest pain.
- Weak Bones: Liothyronine may cause reduced bone density (osteopenia) and increase the risk of fractures due to osteoporosis.
Who Should Not Use Liothyronine?
Liothyronine is not suitable for everyone. It is contraindicated in the following cases:
- Allergies: Individuals allergic to liothyronine, Cytomel, or any ingredients in the specific product.
- Untreated Reduced Adrenal Function (Adrenal Insufficiency): Liothyronine should not be taken if adrenal function is reduced and not being treated.
Important Considerations Before Taking Liothyronine
General Precautions
- Only take liothyronine if prescribed by a healthcare provider.
- Take it exactly as prescribed.
- Do not use liothyronine for weight loss or obesity.
- Keep liothyronine out of the reach of children.
- Elderly individuals may be at greater risk of side effects.
Information to Share with Your Healthcare Provider
Before starting liothyronine, inform your healthcare provider about all health conditions and medications you are taking, including:
- Any food allergies
- Heart or blood vessel disease
- Reduced adrenal function
- Diabetes
- Thyroid nodules
- Subacute thyroiditis
- Myxedema coma
- Low red blood cell levels (anemia)
- Weak bones (osteoporosis)
- Post-menopausal status
- Upcoming surgery or dental procedures
- Pituitary problems
- Clotting problems
- Pregnancy or plans to become pregnant
- Breastfeeding or plans to breastfeed
Potential Interactions
Liothyronine can interact with various medications and supplements. Discuss the use of the following with your healthcare provider:
- Slow-release nicotinic acid
- Bile acid sequestrants (e.g., colestipol, cholestyramine, colesevelam)
- Kayexalate
- Sevelamer
- Hormones (e.g., estrogen, testosterone)
- Methadone
- Chemotherapy agents (e.g., 5-fluorouracil, asparaginase, mitotane, tamoxifen, tyrosine kinase inhibitors)
- Corticosteroids (e.g., dexamethasone, methylprednisolone, prednisone)
- Salicylates (e.g., diflunisal, salsalate)
- Phenobarbital
- Nonsteroidal anti-inflammatory drugs (NSAIDs)
- Rifampin
- Beta-blockers (e.g., atenolol, metoprolol, propranolol)
- Digoxin
- Amiodarone
- Diabetes medications
- Blood thinners
- Tricyclic antidepressants or maprotiline
- Weight loss medications (e.g., diethylpropion, phendimetrazine, phentermine)
Liothyronine in Thyroid Hormone Replacement Therapy
Understanding T3 and T4
Thyroid hormones, primarily T3 and T4, are essential for regulating metabolism. T4 is often referred to as the storage form, while T3 is the active form. T4 gets converted into T3 in the body, but this conversion isn't always efficient for everyone, which is why some individuals may require additional T3 supplementation.
The Role of T3
T3 is the active form of thyroid hormone and plays a vital role in various bodily functions, including energy levels, mood, and weight management. When T3 levels are optimal, you might notice improved energy, better mood stability, and even enhanced cognitive function.
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Potential Benefits of T3 Supplementation
Patients transitioning to T3 often report a remarkable enhancement in their overall well-being. This can manifest in various ways, including heightened energy, clearer thinking, and an improved sense of vitality. In addition, many individuals note that T3 helps with motivation and focus.
Considerations for T3 Use
- Symptom Monitoring: Keep a symptom diary to track any fluctuations in energy levels, mood, or weight changes.
- Regular Check-ups: Regular visits to your doctor are essential to check progress and monitor for unwanted effects through blood tests.
- Communication with Healthcare Provider: An open dialogue where you can express your symptoms, experiences, and goals is invaluable.
Why Some Patients Need T3
In cases where patients have been on thyroid hormone replacement therapy but still feel ‘off,’ doctors may explore the option of adding T3. For those who are prescribed T3, there may be several advantages.
Potential Adverse Effects of T3 Therapy
- Heart Failure and Stroke: One study found that the use of L-T3 (alone or in combination with L-T4), compared to L-T4 alone, was associated with increased risk of heart failure and stroke, but not osteoporosis, cancer or atrial fibrillation.
Desiccated Thyroid Extract
Desiccated (dried and powdered) thyroid extract obtained from pigs or cows, was a common and inexpensive form of thyroid therapy before the individual active thyroid hormones were discovered. It is currently available for purchase as a supplement, or by prescription as a medication (Armour®, NatureThyroid®, NP Thyroid®). Since pills made from animal thyroid are not purified, they contain hormones and proteins that do not exist in the body outside of the thyroid gland. Desiccated thyroid contains both T4 and T3, however the balance of T4 and T3 in animals is different from the human thyroid. The amounts of both T4 and T3 can vary in every batch of desiccated thyroid, making it harder to keep blood levels stable throughout the day. Desiccated thyroid pills contain chemicals (binders) to hold the pill together, so they are not completely “natural”. Animal thyroid extract should not be used in pregnancy, as the T3 portion does not reach the developing baby.
T3 Monotherapy
A preparation of synthetic T3 (Cytomel®) is available. After taking a tablet of Cytomel® there are very high levels of T3 for a short time, and then the levels decrease very rapidly in the bloodstream. This means that T3 has to be taken several times each day, but even this does not smooth out the T3 levels entirely. In addition, it is impossible to avoid having too much thyroid hormone in the system soon after each dose of T3 is taken. High T3 levels can lead to unpleasant symptoms such as rapid heartbeat, insomnia and anxiety. High T3 levels also can possibly harm the heart and the bones. Another concern with using T3 treatment is that the body is deprived of the ability to adjust the conversion of T4 to T3 to regulate the supply of T3 according to the body’s own needs.
Combination Therapy
Some hormone preparations containing both T4 and T3 are available in the United States (Thyrolar ®). Combination T4/T3 preparations contain much more T3 than is usually produced naturally within the body. Because of this, they can have the same side effects as T3 given by itself. It is also given once a day, despite the short life span of T3 in the body.
T3 for normal thyroid
Some people with normal thyroid blood tests have symptoms that are similar to symptoms of hypothyroidism. Several scientific studies have looked at whether T4 therapy would be of benefit to patients with symptoms that overlap with hypothyroid symptoms and normal thyroid function. There has been no proven benefit in taking T4 for improving symptoms if thyroid hormone levels are normal.
Potential Side Effects and Management of T3 Supplements
As with any medication, T3 can have side effects. Some people may experience side effects such as insomnia, anxiety, or increased heart rate when starting T3. These side effects can feel daunting, but they often diminish as your body adjusts. It’s also essential to regularly check thyroid hormone levels if you’re on T3, as the balance of T3 and T4 is finely tuned in your body.
Minimizing Side Effects
- Start with a Low Dose: When it comes to your thyroid, you always want to start low and go slow. This is especially important if you are someone who tends to be sensitive. Remember: there’s no rush. Take your time and find what dose works best for you.
- Take with Food: Taking your T3 supplement with food will help minimize any indigestion that can occur with certain ingredients like zinc and botanicals, which tend to be harder on the stomach.
- Monitor Your Symptoms: Always pay attention to how you are feeling. If you don’t notice any difference after 4-6 weeks, increase your dose.
- Digestive Discomfort: This is probably due to the dose of zinc and selenium which can sometimes upset the stomach.
- Temporary Fatigue: If your body has been in a state of fatigue for a long period of time, a sudden increase in T3 may lead to temporary fatigue as your body adjusts.
- Mild Jitteriness: Some thyroid patients have reported a feeling of being on edge, especially when they first start taking it.
- No benefit at all: As mentioned, about 5-10% of people who take T3 supplements will not see any benefit at all.
When to Seek Medical Attention
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.
Liothyronine and Specific Conditions
Diabetes
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.
Pregnancy and Breastfeeding
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.
Hair Loss
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.
Interactions with Other Medications
Liothyronine interacts with many other medicines. Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.
Thyroid Hormone Replacement Therapy
Levothyroxine monotherapy has been the standard of care for treatment of hypothyroidism for more than 40 years. However, patients treated with levothyroxine have relatively lower serum tri-iodothyronine (T3) concentrations than the general population, and symptoms of hypothyroidism persist for some patients despite normalisation of thyroidstimulating hormone (TSH) concentrations. The understanding that maintenance of normal T3 concentrations is the priority for the thyroid axis has redirected the clinical focus to serum T3 concentrations in patients with hypothyroidism.
Serum Thyroid Hormone Concentrations
Serum thyroid hormone concentrations present a low intraindividual variability over time in adult life. Steadystate thyroid hormone concentrations in an individual are determined by the specific setpoint of the HPT axis, which is affected by genetic and environmental factors. Serum T3 also has a circadian rhythmicity that follows the TSH circadian variation, with about 10% higher concentrations in the early morning hours.
The Role of Deiodinases
The discrepancy between normal TSH and impaired peripheral thyroid hormone action in some levothyroxine-treated patients, suggests that the T4-to-T3 conversion by peripheral deiodinases is unable to restore appropriate intracellular T3 to all tissues. Thus, some patients treated with levothyroxine might benefit from T3 supplementation.
Genetic Factors
Predicting which patients would benefit from combination therapy with levothyroxine and liothyronine remains clinically challenging, particularly because residual hypothyroidlike symptoms are not specific to levothyroxine-treated patients with normal TSH, and might be seen in patients with diabetes, depression, sleep apnoea, vitamin D and B12 deficiency, chronic fatigue syndrome, and adrenal insufficiency-especially in patients with autoimmune thyroiditis.