What are the long-term side effects of levothyroxine
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Long-Term Side Effects of Levothyroxine
Levothyroxine, a synthetic thyroid hormone, is commonly prescribed for conditions such as hypothyroidism and thyroid nodules. While effective in managing these conditions, long-term use of levothyroxine can lead to several side effects. This article synthesizes findings from multiple studies to highlight the long-term side effects of levothyroxine.
Cardiovascular Side Effects
Increased Heart Rate and Atrial Premature Beats
Long-term levothyroxine therapy, especially at suppressive doses, has been shown to significantly affect cardiac function. Patients on long-term therapy exhibited an increased average heart rate and a higher prevalence of atrial premature beats compared to control groups . Additionally, there was an observed increase in left ventricular mass index and enhanced left ventricular systolic function, indicating potential cardiac hypertrophy and increased cardiac workload .
No Significant Change in Cardiovascular Events
In older adults with subclinical hypothyroidism, levothyroxine treatment did not significantly alter the risk of cardiovascular events, including atrial fibrillation, heart failure, or all-cause mortality. This was consistent regardless of the patients' history of cardiovascular disease and age . This suggests that while levothyroxine may affect certain cardiac parameters, it does not necessarily translate to an increased risk of major cardiovascular events in this population.
Thyroid and Nodule Changes
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. In a study over five years, patients receiving levothyroxine showed a decrease in nodule volume and a significantly lower incidence of new nodules compared to the control group . However, the therapy was associated with prolonged TSH suppression, which can lead to unfavorable side effects, suggesting that such treatment should be reserved for specific cases, such as small nodules in younger patients .
Mental Health and Tolerability
Subjective Response and Tolerability
In patients with refractory mood disorders, long-term use of supraphysiological doses of levothyroxine was generally well-tolerated. Patients reported a positive subjective response, and the overall side effect profile was favorable, with physical and mental symptoms only slightly higher than in the general population . This indicates that, for certain psychiatric conditions, levothyroxine can be a viable long-term treatment option with manageable side effects.
Conclusion
Long-term levothyroxine therapy can lead to several side effects, particularly affecting cardiac function and thyroid nodule dynamics. While it does not significantly increase the risk of major cardiovascular events in older adults with subclinical hypothyroidism, it can cause increased heart rate and atrial premature beats. Additionally, it is effective in reducing thyroid nodule volume and preventing new nodules but should be used cautiously due to potential side effects from prolonged TSH suppression. For patients with refractory mood disorders, the therapy is generally well-tolerated and can provide significant benefits.
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