Should You Stop Methimazole with TSH at 3.767 µIU/mL?
No, do not stop methimazole when TSH is 3.767 µIU/mL—this value falls within the normal reference range (0.45–4.5 mIU/mL) and indicates you are currently euthyroid on treatment. Stopping methimazole at this point would risk recurrence of hyperthyroidism 1, 2.
Understanding Your Current Thyroid Status
Your TSH of 3.767 µIU/mL is normal, confirming that methimazole has successfully controlled your hyperthyroidism and you are now in a euthyroid (normal thyroid function) state 3.
The normal TSH reference range is 0.45–4.5 mIU/mL, and your value sits comfortably in the middle of this range, indicating appropriate thyroid hormone levels 3.
This TSH level does NOT indicate hypothyroidism—hypothyroidism would be diagnosed with TSH >4.5 mIU/mL (particularly >10 mIU/mL) along with low or low-normal free T4 3, 1.
When to Actually Stop or Adjust Methimazole
Continue Current Dose When:
- TSH is 0.5–4.5 mIU/mL with normal free T4 (your current situation)—this indicates optimal control 1, 4.
Reduce Methimazole Dose When:
- TSH rises above 4.5 mIU/mL but remains <10 mIU/mL and you are asymptomatic—consider dose reduction rather than complete discontinuation 1.
Stop or Significantly Reduce Methimazole When:
- TSH exceeds 10 mIU/mL or you develop symptoms of hypothyroidism (fatigue, weight gain, cold intolerance, constipation)—this indicates methimazole has caused iatrogenic hypothyroidism 1.
- You have completed 12–18 months of treatment and your physician determines you are a candidate for a trial off medication (though 58% of patients relapse after stopping) 5.
Critical Monitoring Requirements
Check both TSH AND free T4 every 4–6 weeks during the initial treatment phase to ensure you remain euthyroid 1, 4.
Once stabilized on maintenance therapy (like you appear to be now), monitoring can be reduced to every 6–12 months 1.
Free T4 is essential because TSH normalization lags behind free T4 during treatment—you need both values to accurately assess thyroid status 1.
Why Stopping Now Would Be Dangerous
Graves' disease has a 58% relapse rate after stopping methimazole, even after 18 months of treatment 5.
Premature discontinuation will likely result in recurrent hyperthyroidism within 3–7 months, requiring you to restart treatment 5.
Your current euthyroid state on methimazole indicates the medication is working appropriately—there is no medical indication to stop 1, 4.
Long-Term Treatment Considerations
Low-dose methimazole (1.25–2.5 mg daily) can safely maintain euthyroidism for decades without adverse events in patients who relapse after discontinuation 6.
If you have already experienced multiple relapses, long-term low-dose methimazole is a reasonable and effective strategy 6.
Definitive treatment options (radioactive iodine or thyroidectomy) should be considered if you prefer not to remain on long-term methimazole or if you experience recurrent relapses 1.
Critical Safety Warnings from FDA Label
Immediately report fever, sore throat, or signs of infection to your physician, as methimazole can cause life-threatening agranulocytosis 2.
Report new rash, decreased urine output, shortness of breath, or coughing up blood, as methimazole can cause severe vasculitis 2.
Methimazole requires close surveillance with periodic monitoring of thyroid function tests and complete blood counts 2.
Common Pitfalls to Avoid
Never stop methimazole based solely on TSH without checking free T4—you need both values to make treatment decisions 1.
Do not assume a normal TSH means you can discontinue treatment—Graves' disease is a chronic autoimmune condition that often requires prolonged therapy 5, 6.
Avoid overreacting to isolated TSH values—TSH normalization lags behind free T4, so a single measurement may not reflect your true thyroid status 1.