Liothyronine – Cytomel
Thyroid hormones are naturally produced in the body; however, many pharmaceutical companies synthesize these hormones artificially due to their simplicity. There are two main types of thyroid hormones: T4, also known as levothyroxine, and T3, known as liothyronine. Both types are produced and stored in the thyroid gland.
Thyroid hormones from pharmaceutical sources are obtained through two methods: derived from animal thyroid glands (bovine or ovine) or synthesized. In the USA, the iodine content in thyroid preparations is strictly regulated.
Cytomel (liothyronine sodium) is available as a tablet or as a salt form of a naturally occurring thyroid hormone. T3 is significantly more potent than T4.
Pharmacology
The exact mechanisms of how thyroid hormones function remain somewhat elusive, but their actions involve a myriad of biochemical transformations within cells. They primarily provide energy, enhancing the consumption of carbohydrates, lipids, and proteins while increasing oxygen usage. Individuals taking thyroid hormones generally experience an elevated basal metabolic rate, impacting nearly every organ, including the brain. The critical role of thyroid hormones is often highlighted when observing patients with deficiencies.
Dosage
Thyroid hormones are effectively absorbed from the stomach into the bloodstream with a rapid onset of action, typically within hours, although peak activity may take several days. These hormones can remain in the body for days post-administration as they bind with albumin in the blood, thus avoiding breakdown by the liver.
Indications for thyroid hormone include:
- Replacement therapy for hypothyroidism
- Post-thyroidectomy replacement therapy
- Treatment for goiters and thyroid nodules
- Diagnostic agents in suppression tests to differentiate suspected hyperthyroidism
- Cytomel tablets as an alternative for those allergic to pork or beef thyroid
Body Builders and Weight Loss
For decades, athletes have misused thyroid hormones for weight loss due to their fat and carbohydrate combusting effects. Cytomel has found its place in various sports, often taken orally for 4-6 weeks, then discontinued before competitions. While Cytomel can serve as an effective fat burner and performance enhancer, it is crucial to note that many athletes also combine it with numerous other supplements.
Online sources often recommend a starting dose of 25 mcg/day for those pursuing weight loss, with gradual increments of 5-10 mcg/day. The maximum dose without side effects is approximately 100 mcg/day. Anecdotal reports suggest a timeframe of 6-12 weeks for weight loss with Cytomel. However, once discontinued, users may experience thyroid insufficiency due to the suppression of natural hormone production. Therefore, a gradual dose taper is advisable.
Consulting a physician is crucial for those considering off-label thyroid hormone use for weight loss to ensure safety.
Signs and Symptoms
Excessive levels of thyroid hormone can lead to various side effects, including:
- Headache
- Mood changes—irritability, anxiety, nervousness
- Excessive sweating
- Abnormal heart rhythms
- Palpitations
- Chest pain
- Diarrhea
- Menstrual irregularities
- Heart failure exacerbation
- Shock
Severe overdosing can induce symptoms similar to a thyroid storm, while chronic overdosage may result in hyperthyroidism symptoms.
Contraindications
Thyroid hormone is generally contraindicated for individuals with untreated adrenal cortical insufficiency or thyrotoxicosis and those with hypersensitivity to any active components. True allergic reactions to liothyronine are believed to be rare.
Signs and Symptoms
Many seek thyroid hormones for weight loss, often in combination with other supplements. Typical therapeutic doses are generally ineffective for weight loss, necessitating larger doses that can pose serious risks and potentially life-threatening symptoms, especially when combined with other agents like ephedrine or growth hormone.
Caution is warranted for patients with certain medical conditions, as thyroid hormones can exacerbate adrenal insufficiency and impact diabetes management. Additionally, they may enhance the effects of oral anticoagulants, increasing bleeding risks.
Non-medical professionals sometimes recommend thyroid hormones for infertility treatment, but scientific support for this use is nonexistent.
Thyroid hormones can have significant side effects; therefore, individuals with cardiovascular issues must consult with a physician before starting therapy, and only the lowest effective dose should be employed.
Levels
Thyroid hormone levels are easily monitored. Sporting agencies, including the IOC and WADA, routinely test athletes for these hormones. Sensitive radioimmunoassays can detect even minute quantities in urine.
Drug Interactions
Liothyronine interacts with several medications, including:
- Oral anticoagulants
- Insulin or antihyperglycemics
- Cholestyramine
- Estrogen, oral contraceptives
- Tricyclic antidepressants
- Digitalis
Physicians must ensure that thyroid hormone dosages remain appropriate. Regular monitoring of patients taking these hormones is essential.
Treatment of Overdosage
In cases of suspected thyroid hormone overdose, the patient should be hospitalized, with hormone intake temporarily halted and observation initiated. Most require a cessation period of 4-8 weeks for the thyroid gland’s recovery. Supportive care is the primary approach, as no specific antidotes exist. Inducing vomiting is not recommended due to aspiration risk. Comatose individuals may require temporary mechanical ventilation. Generally, fluid resuscitation and oxygen provision, alongside monitoring, are sufficient. In some cases, beta-adrenergic blockers may be necessary to mitigate sympathetic drive.
Dosage
Liothyronine is available as a tablet, administered once daily. Dosage is determined by the severity of hypothyroidism, with therapy commencing at the lowest effective dose given its rapid action. The initial dosage of Cytomel (liothyronine sodium) is 5 mcg/day, increasing by no more than 5 mcg/day every 2-3 weeks. Starting too high or making abrupt increases can worsen preexisting heart conditions, with typical effective doses ranging from 50-75 mcg/day. Liothyronine is also available in intravenous form, occasionally utilized for treating myxedema coma, a serious complication of hypothyroidism predominantly seen in elderly, often female, patients.
Liothyronine is offered in 5, 25, and 50 mcg tablets, available only by prescription in the USA.
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