From the Guidelines
Yes, a person taking too much levothyroxine can experience palpitations as a common symptom of overtreatment. Levothyroxine is a medication used to replace thyroid hormone in people with hypothyroidism, but excessive doses can lead to symptoms of hyperthyroidism. Palpitations occur because excess thyroid hormone increases heart rate and contractility, making the heart beat faster and sometimes irregularly, as reported in a study published in JAMA 1. Other symptoms of levothyroxine overtreatment may include anxiety, tremors, insomnia, weight loss, heat intolerance, and increased sweating.
Causes and Mechanisms
The mechanism behind palpitations in levothyroxine overtreatment is related to the increase in heart rate and cardiac contractility due to excess thyroid hormone. This can lead to atrial arrhythmias, as noted in a study published in the Journal of the American College of Cardiology 1. However, the prevalence of ventricular arrhythmias does not increase significantly with subclinical hyperthyroidism, according to a scientific review and guidelines for diagnosis and management published in JAMA 1.
Management and Treatment
If you experience palpitations while taking levothyroxine, you should contact your healthcare provider promptly. They will likely check your thyroid function with blood tests measuring TSH and possibly T4 levels to determine if your dose needs adjustment. Never adjust your levothyroxine dose on your own, as proper thyroid hormone balance is crucial for many bodily functions and requires medical supervision. In some cases, beta-blockers may be recommended to control the ventricular rate, especially in situations where a beta blocker cannot be used, a nondihydropyridine calcium channel antagonist is recommended, as suggested by the 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation 1.
Key Considerations
- Proper dosing: It is essential to follow the prescribed dose of levothyroxine to avoid overtreatment and its associated symptoms, including palpitations.
- Monitoring: Regular monitoring of thyroid function is crucial for patients on levothyroxine to prevent and manage overtreatment.
- Medical Supervision: Any adjustments to levothyroxine dosage should be made under the guidance of a healthcare provider to ensure proper thyroid hormone balance and prevent complications.
From the FDA Drug Label
Adverse reactions associated with levothyroxine sodium therapy are primarily those of hyperthyroidism due to therapeutic overdosage They include the following: • General: fatigue, increased appetite, weight loss, heat intolerance, fever, excessive sweating • Central nervous system: headache, hyperactivity, nervousness, anxiety, irritability, emotional lability, insomnia • Musculoskeletal: tremors, muscle weakness, muscle spasm • Cardiovascular: palpitations, tachycardia, arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, cardiac arrest • Respiratory: dyspnea • Gastrointestinal: diarrhea, vomiting, abdominal cramps, elevations in liver function tests • Dermatologic: hair loss, flushing, rash • Endocrine: decreased bone mineral density • Reproductive: menstrual irregularities, impaired fertility
A person on too much levothyroxine can have palpitations as it is one of the adverse reactions associated with levothyroxine sodium therapy due to therapeutic overdosage 2.
From the Research
Levothyroxine and Palpitations
- Levothyroxine is a medication used to treat hypothyroidism, and it can have dual effects on the body, including substituting thyroid hormone deficiency and suppressing malignancy spreading in cancer 3.
- High doses of levothyroxine can increase the risk of cardiac arrhythmias, particularly atrial fibrillation, especially in patients with pre-existing heart diseases 3, 4.
- Hyperthyroidism, which can be caused by excessive levothyroxine intake, is associated with an increased risk of cardiac arrhythmias, including atrial fibrillation and sinus tachycardia 4, 5.
- Palpitations, caused by sinus tachycardia and occasionally by atrial fibrillation, are a common cardiovascular symptom of thyrotoxicosis, which can be caused by excessive levothyroxine intake 5.
- The relationship between thyroid disease, including hyperthyroidism caused by excessive levothyroxine intake, and atrial fibrillation is well-established, and the underlying biochemical mechanisms are being researched 6.
Risk of Cardiac Arrhythmias
- The risk of cardiac arrhythmias, including atrial fibrillation, increases with high doses of levothyroxine, especially in patients with pre-existing heart diseases 3, 4.
- Levothyroxine treatment in patients with subclinical hypothyroidism and heart disease was not associated with a significant benefit or risk of all-cause mortality, major adverse cardiac events, or hospital admission in one study 7.
- However, other studies suggest that excessive levothyroxine intake can increase the risk of cardiac arrhythmias, including atrial fibrillation and sinus tachycardia 4, 5, 6.