Long term side effects of levothyroxine
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Long-Term Side Effects of Levothyroxine
Introduction to Levothyroxine and Its Uses
Levothyroxine is a synthetic thyroid hormone commonly prescribed for hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. While it is effective in managing thyroid hormone levels, long-term use of levothyroxine can have various side effects, particularly when used in supraphysiological doses or for thyroid hormone suppression.
Cardiovascular Side Effects of Long-Term Levothyroxine Use
Cardiac Function and Arrhythmias
Long-term use of levothyroxine, especially at suppressive doses, can significantly impact cardiac function. Studies have shown that patients on long-term levothyroxine therapy exhibit increased heart rates and a higher prevalence of atrial premature beats compared to controls. Additionally, echocardiographic evaluations have revealed increased left ventricular mass index and enhanced left ventricular systolic function in these patients . These findings suggest that while levothyroxine is effective in managing thyroid hormone levels, it can lead to cardiac hypertrophy and arrhythmias over time.
Cardiovascular Outcomes in Older Adults
In older adults with subclinical hypothyroidism, levothyroxine treatment does not significantly alter the risk of cardiovascular events, including atrial fibrillation and heart failure. This was concluded from pooled data of two randomized controlled trials, which found no significant difference in cardiovascular outcomes between those treated with levothyroxine and those given a placebo . This indicates that while levothyroxine may not exacerbate cardiovascular risks in older adults, it also does not provide significant cardiovascular benefits.
Impact on Thyroid Nodules and Goiter
Nodule Volume and New Nodule Formation
Levothyroxine suppressive therapy has been shown to reduce the volume of thyroid nodules and prevent the formation of new nodules in patients with benign cold thyroid nodules. Over a five-year period, patients receiving levothyroxine experienced a decrease in nodule volume and fewer new nodules compared to a control group . However, the therapy should be reserved for younger patients with small nodules due to the potential for unfavorable side effects associated with prolonged TSH suppression.
Effects on Mental and Physical Health
Mood Disorders and Tolerability
In patients with refractory mood and schizoaffective disorders, long-term use of supraphysiological doses of levothyroxine has been associated with a favorable side effect profile. Patients reported positive subjective responses and only slightly higher general physical and mental symptoms compared to the general population . This suggests that, for certain psychiatric conditions, levothyroxine can be well-tolerated and beneficial.
Lipid Profile and Metabolic Effects
For older patients with subclinical hypothyroidism, levothyroxine treatment has been shown to significantly reduce cholesterol levels, including total cholesterol, triglycerides, low-density lipoprotein cholesterol, and apolipoprotein B. However, it does not significantly affect bone mineral density, fatigue, quality of life, cognitive function, or blood pressure . This indicates that while levothyroxine can improve lipid profiles, its broader metabolic and quality-of-life impacts are limited.
Reproductive Health
Pregnancy Outcomes
Levothyroxine supplementation in pregnant women with subclinical hypothyroidism and thyroid autoimmunity has been found to reduce the risks of pregnancy loss and preterm birth. This effect is more pronounced in naturally conceived pregnancies compared to those achieved through assisted reproduction . These findings highlight the importance of levothyroxine in managing thyroid-related pregnancy complications.
Conclusion
Long-term use of levothyroxine, particularly at suppressive doses, can have significant side effects, including impacts on cardiac function, thyroid nodule management, and lipid profiles. While it is generally well-tolerated in patients with mood disorders and can improve pregnancy outcomes in women with thyroid autoimmunity, careful monitoring and patient selection are crucial to minimize potential adverse effects.
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