Levothyroxine side effects long term
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Long-Term Side Effects of Levothyroxine: A Comprehensive Review
Introduction to Levothyroxine and Its Uses
Levothyroxine is a synthetic thyroid hormone commonly prescribed for hypothyroidism and other thyroid-related disorders. While it is effective in managing thyroid hormone levels, long-term use can lead to various side effects, particularly when used in supraphysiological doses or for thyroid hormone suppression.
Cardiovascular Side Effects of Long-Term Levothyroxine Use
Increased Heart Rate and Atrial Premature Beats
Long-term levothyroxine therapy, especially at suppressive doses, has been shown to significantly affect cardiac function. Studies have reported an increase in average heart rate and a higher prevalence of atrial premature beats among patients undergoing such treatment 35. These cardiac changes are critical considerations for patients with pre-existing heart conditions.
Left Ventricular Hypertrophy and Systolic Function
Patients on long-term levothyroxine therapy also exhibit increased left ventricular mass index and enhanced left ventricular systolic function. These changes indicate a potential risk for developing left ventricular hypertrophy, which can lead to further cardiovascular complications 35.
Cardiovascular Outcomes in Older Adults
In older adults with subclinical hypothyroidism, levothyroxine treatment did not significantly alter the risk of cardiovascular events, including atrial fibrillation and heart failure. This finding suggests that while levothyroxine may not exacerbate cardiovascular risks in this population, it also does not provide significant cardiovascular benefits 46.
Effects on Thyroid Nodules and Goiter
Nodule Volume and New Nodule Formation
Levothyroxine suppressive therapy has been effective in reducing the volume of thyroid nodules and preventing the formation of new nodules. However, this benefit is more pronounced in patients with complete TSH suppression. Despite these positive outcomes, the therapy should be reserved for younger patients with small nodules due to the potential for unfavorable side effects .
Impact on Mental and Physical Health
Subjective Response and Tolerability
Patients with refractory mood and schizoaffective disorders treated with long-term supraphysiological doses of levothyroxine reported a favorable subjective response and side-effect profile. General physical and mental symptoms were only slightly higher than in the general population, indicating good tolerability among responders .
Long-Term Effects in Congenital Hypothyroidism
Diastolic Dysfunction and Exercise Capacity
Young adults with congenital hypothyroidism treated with levothyroxine from infancy showed signs of left ventricular diastolic dysfunction and impaired exercise capacity. These findings highlight the need for careful monitoring of cardiovascular health in this patient group .
Conclusion
Long-term levothyroxine therapy, while effective in managing thyroid hormone levels, can lead to significant cardiovascular side effects, particularly at suppressive doses. These include increased heart rate, atrial premature beats, and left ventricular hypertrophy. In older adults with subclinical hypothyroidism, levothyroxine does not significantly impact cardiovascular outcomes. Additionally, while levothyroxine can reduce thyroid nodule volume and prevent new nodule formation, its use should be carefully considered due to potential side effects. Overall, the benefits and risks of long-term levothyroxine therapy must be weighed carefully, with close monitoring of cardiovascular health and thyroid function.
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