What is the best course of action for a patient with hypothyroidism (underactive thyroid) on levothyroxine (T4) 150 micrograms (mcg) with a Thyroid-Stimulating Hormone (TSH) level of 0.26 mU/L?

Reduce Levothyroxine Dose Immediately

Your current levothyroxine dose of 150 mcg is excessive and must be reduced immediately—a TSH of 0.26 mIU/L indicates iatrogenic subclinical hyperthyroidism that significantly increases your risk for atrial fibrillation, osteoporosis, fractures, and cardiovascular complications. 1

Current Thyroid Status

• Your TSH of 0.26 mIU/L falls below the normal reference range of 0.45-4.5 mIU/L, indicating overtreatment 1
• This represents iatrogenic subclinical hyperthyroidism—a preventable complication affecting approximately 25% of patients on levothyroxine who are unintentionally maintained on excessive doses 1
• The target TSH for primary hypothyroidism should be 0.5-4.5 mIU/L with normal free T4 levels 1

Immediate Dose Reduction Required

Reduce your levothyroxine dose by 12.5-25 mcg immediately (from 150 mcg to either 137.5 mcg or 125 mcg) 1

• For TSH between 0.1-0.45 mIU/L, a reduction of 12.5-25 mcg is appropriate 1
• The smaller reduction (12.5 mcg) is preferred if you are over 70 years old or have cardiac disease 1
• The larger reduction (25 mcg) is appropriate if you are younger without cardiac risk factors 1

Serious Health Risks of Continued Overtreatment

Cardiovascular Complications

• Atrial fibrillation risk increases 5-fold in patients ≥45 years with TSH <0.4 mIU/L 1
• Prolonged TSH suppression increases risk for other cardiac arrhythmias and potential cardiovascular mortality 1
• Left ventricular hypertrophy and abnormal cardiac output may develop with long-term TSH suppression 1

Bone Health Complications

• Accelerated bone loss and osteoporotic fractures, particularly in postmenopausal women 1
• Increased risk of hip and spine fractures in women >65 years with TSH ≤0.1 mIU/L 1
• Loss of bone mineral density occurs even with mild TSH suppression 1

Monitoring After Dose Adjustment

• Recheck TSH and free T4 in 6-8 weeks after dose reduction, as this represents the time needed to reach steady state 1, 2
• Target TSH should be 0.5-4.5 mIU/L with normal free T4 levels 1
• Once adequately treated, repeat testing every 6-12 months or if symptoms change 1

Important Exception

If you have thyroid cancer requiring TSH suppression, do not adjust your dose without consulting your endocrinologist first 1

• Even most thyroid cancer patients should not have TSH this suppressed 1
• Low-risk thyroid cancer patients with excellent response should maintain TSH 0.5-2 mIU/L 1
• Only patients with structural incomplete response may require TSH <0.1 mIU/L 1

Critical Pitfall to Avoid

• Do not wait to reduce the dose—approximately 25% of patients on levothyroxine are inadvertently maintained on excessive doses, and the risks of atrial fibrillation, fractures, and cardiac complications increase with duration of TSH suppression 1
• Ensure adequate calcium (1200 mg/day) and vitamin D (1000 units/day) intake if TSH has been chronically suppressed 1