From the Guidelines
The most commonly recommended thyroid medication is levothyroxine (Synthroid, Levoxyl, Tirosint), a synthetic form of the T4 hormone, which is typically the first-line treatment for hypothyroidism. This recommendation is based on the study by the U.S. Preventive Services Task Force 1, which states that the principal treatment for hypothyroidism is oral T4 monotherapy (levothyroxine sodium).
Treatment Options
Other treatment options include liothyronine (Cytomel) and combination T4/T3 medications like natural desiccated thyroid (NDT) products such as Armour Thyroid or Nature-Throid. However, these options are typically considered for patients who do not respond well to T4-only therapy. The choice between medications depends on the specific condition being treated, individual response, and whether the patient has conversion issues from T4 to T3.
Dosing and Administration
Dosing is individualized based on lab results (TSH, free T4, and sometimes free T3 levels) and symptom response, with adjustments typically made every 6-8 weeks until optimal levels are achieved. Levothyroxine is usually started at 1.6 mcg/kg body weight daily, taken on an empty stomach 30-60 minutes before breakfast. Proper absorption requires taking thyroid medication consistently at the same time daily, avoiding calcium, iron supplements, and certain foods within 4 hours of dosing.
Monitoring and Follow-up
Thyroid medication is generally a lifelong treatment for hypothyroidism, with regular monitoring recommended. Follow-up testing of serum T4 levels in persons with persistently abnormal TSH levels can differentiate between subclinical (normal T4 levels) and “overt” (abnormal T4 levels) thyroid dysfunction, as stated in the study by the U.S. Preventive Services Task Force 1. Additionally, the study by JAMA 1 suggests that levothyroxine therapy is reasonable for patients with subclinical hypothyroidism and serum TSH higher than 10 mIU/L.
Key Considerations
- The optimal screening interval for thyroid dysfunction is unknown 1.
- Treatment is generally recommended for patients with a TSH level that is undetectable or less than 0.1 mIU/L, particularly those with overt Graves disease or nodular thyroid disease 1.
- Important clinical outcomes include cardiovascular- and cancer-related morbidity and mortality, as well as falls, fractures, functional status, and quality of life 1.
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Types of Thyroid Medication
The following types of thyroid medication are recommended:
- Levothyroxine sodium (thyroxine) monotherapy, which provides uniform levels of both thyroxine and triiodothyronine in the circulation without diurnal variation 2
- Liothyronine (triiodothyronine) in combination with levothyroxine sodium for patients who remain symptomatic on levothyroxine therapy 3
- Desiccated thyroid extract, a form of combination therapy with an LT4/LT3 ratio of approximately 4:1 3
Starting Dose of Levothyroxine
The starting dose of levothyroxine can vary depending on the patient's age and medical history:
- A full starting dose of levothyroxine (1.6 mug/kg) can be safe and effective for cardiac asymptomatic patients with primary hypothyroidism 4
- A low starting dose of levothyroxine (25 mug) with gradual titration may be recommended for elderly patients or those with a history of coronary artery disease 2
Combination Therapy with Liothyronine
Combination therapy with liothyronine and levothyroxine may be considered for patients who remain symptomatic on levothyroxine therapy:
- The recommended LT4/LT3 ratio is 13:1-20:1 5
- The goals of combination therapy are to achieve a physiological ratio of free triiodothyronine/free thyroxine (FT3/FT4) and non-suppression of TSH 5
- However, the clinical benefit of combination therapy is not clear, and more studies are needed to evaluate its effectiveness 6