What should I do if I haven't taken levothyroxine (thyroid hormone replacement medication) for a month and am experiencing palpitations (tachycardia)?

Management of Palpitations After Discontinuing Levothyroxine for One Month

You should immediately resume your levothyroxine at your previously prescribed dose and seek urgent medical attention for evaluation of your palpitations, as discontinuing thyroid hormone replacement can lead to serious cardiac complications. 1

Understanding the Risks of Discontinuing Levothyroxine

Stopping levothyroxine for a month can lead to significant hypothyroidism, which paradoxically can cause cardiac symptoms including palpitations. While hyperthyroidism is more commonly associated with tachycardia and palpitations, severe hypothyroidism can also trigger arrhythmias, particularly supraventricular tachycardias 2.

The FDA drug label for levothyroxine clearly warns that both overtreatment and undertreatment with levothyroxine can have negative effects on cardiovascular function 1. Specifically:

• Undertreatment (which occurs when medication is stopped) can lead to various cardiac manifestations
• Cardiac symptoms that develop or worsen require immediate dose adjustment and medical evaluation

Immediate Steps to Take

1. Resume your levothyroxine immediately at your previously prescribed dose
2. Seek urgent medical care for evaluation of your palpitations
3. Do not attempt to adjust the dose yourself without medical supervision

Medical Evaluation Needed

Your healthcare provider should:

• Perform a 12-lead ECG to document any arrhythmia 3
• Check thyroid function tests (TSH, free T4, and possibly T3)
• Consider a 24-hour Holter monitor or event recorder if palpitations are intermittent 3
• Evaluate for other potential causes of palpitations

Why This Happens

When levothyroxine is discontinued:

1. TSH levels rise as the body attempts to stimulate the thyroid
2. In patients dependent on thyroid replacement, this leads to hypothyroidism
3. Severe hypothyroidism can affect cardiac function through multiple mechanisms:
   • Changes in systemic vascular resistance
   • Activation of the renin-angiotensin-aldosterone system
   • Increased blood volume (up to 25% in thyroid dysfunction) 3
   • Potential development of pulmonary hypertension 3

Resuming Treatment Safely

After restarting levothyroxine:

• Your healthcare provider should monitor your thyroid levels within 4-6 weeks 1
• Dose adjustments may be necessary based on symptoms and lab results
• If cardiac symptoms persist, your provider may consider:
  • Temporary beta-blocker therapy to control heart rate 3
  • Gradual titration of levothyroxine dose to avoid cardiac stress

Prevention of Future Episodes

To prevent similar episodes in the future:

• Never discontinue levothyroxine without medical supervision
• If you experience side effects, consult your provider rather than stopping medication
• Consider alternative timing of levothyroxine intake (evening instead of morning) if absorption is an issue 4
• Maintain regular follow-up appointments for thyroid monitoring 5

Special Considerations

If you have pre-existing heart disease, the risks of both discontinuing and restarting levothyroxine are greater. Your provider may need to:

• Restart at a lower dose (12.5-50 mcg/day) if you're over 60 or have heart disease 6
• Monitor more frequently for cardiac arrhythmias 1
• Consider hospitalization if symptoms are severe or if myxedema coma is suspected 1

Remember that thyroid hormone replacement requires lifelong therapy with careful dose adjustments throughout your lifetime 5. Stopping treatment abruptly can lead to serious complications that may take time to resolve even after restarting medication.