How do you adjust levothyroxine (T4) medication for hypothyroidism?

Adjusting Levothyroxine for Hypothyroidism

Adjust levothyroxine dose by 12.5-25 mcg increments based on TSH levels, recheck TSH in 6-8 weeks after each adjustment, and target a TSH within the reference range (0.5-4.5 mIU/L) for most patients. 1

Initial Dosing Strategy

Starting dose depends critically on age and cardiac status:

• For patients <70 years without cardiac disease: Start with full replacement dose of approximately 1.6 mcg/kg/day 1, 2
• For patients >70 years or with cardiac disease/multiple comorbidities: Start with 25-50 mcg/day and titrate gradually 1, 2

Dose Adjustment Algorithm

When TSH is elevated (inadequate treatment):

• Use 12.5-25 mcg increments based on current dose and patient characteristics 1
• For younger patients (<70 years) without cardiac disease, use 25 mcg increments 1
• For elderly patients (>70 years) or those with cardiac disease, use smaller 12.5 mcg increments to avoid cardiac complications 1
• Larger adjustments risk overtreatment and should be avoided 1

When TSH is suppressed (overtreatment):

• For TSH <0.1 mIU/L: Decrease dose by 25-50 mcg 1
• For TSH 0.1-0.4 mIU/L: Decrease dose by 12.5-25 mcg 1
• First confirm the indication for therapy—patients with thyroid cancer may require intentional TSH suppression 1

Monitoring Protocol

Critical timing for TSH rechecking:

• Recheck TSH every 6-8 weeks after any dose adjustment until target is achieved 1, 2, 3
• Wait the full 6-8 weeks before making further adjustments—adjusting too frequently before reaching steady state is a common pitfall 1
• Once stable on appropriate dose, monitor TSH every 6-12 months 1, 2
• Free T4 can help interpret persistent abnormal TSH levels, as TSH may take longer to normalize 1, 2

Exception for high-risk patients: Those with atrial fibrillation, cardiac disease, or serious medical conditions may warrant more frequent monitoring—consider repeating within 2 weeks 1

Target TSH Levels

For primary hypothyroidism: Target TSH 0.5-4.5 mIU/L (within reference range) 1

Special populations requiring different targets:

• Pregnant women: Maintain TSH in trimester-specific reference range; increase dose by 12.5-25 mcg per day as needed, monitoring TSH every 4 weeks 3
• Thyroid cancer patients (intermediate/high-risk): Target TSH 0.1-0.5 mIU/L for mild suppression 1
• Thyroid cancer patients (structural incomplete response): Target TSH <0.1 mIU/L for aggressive suppression 1

Treatment Thresholds Based on TSH Level

TSH >10 mIU/L: Initiate or increase levothyroxine regardless of symptoms—this level carries approximately 5% annual risk of progression to overt hypothyroidism 1, 2

TSH 4.5-10 mIU/L: Monitor every 4-6 weeks without treatment if asymptomatic; consider treatment trial if symptomatic 1, 2

TSH <0.1 mIU/L on therapy: Reduce dose immediately to prevent complications of iatrogenic hyperthyroidism 1

Common Pitfalls to Avoid

Adjusting doses too frequently: Always wait 6-8 weeks between adjustments to allow levothyroxine to reach steady state 1, 3

Excessive dose increases: Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, increasing risks for osteoporosis, fractures, and atrial fibrillation 1

Ignoring medication interactions: Iron and calcium reduce levothyroxine absorption; enzyme inducers reduce efficacy 4

Failing to distinguish treatment indications: Patients with thyroid cancer requiring TSH suppression need different targets than those with primary hypothyroidism 1

Risks of Improper Dosing

Undertreatment consequences:

• Persistent hypothyroid symptoms 1
• Adverse cardiovascular effects 1
• Abnormal lipid metabolism 1
• Reduced quality of life 1

Overtreatment consequences:

• Atrial fibrillation and cardiac arrhythmias, especially in elderly 1, 2
• Osteoporosis and increased fracture risk 1, 2
• Left ventricular hypertrophy 1
• Bone demineralization in postmenopausal women 1

Pregnancy Considerations

Pre-existing hypothyroidism: Increase levothyroxine dose by 12.5-25 mcg per day when pregnancy confirmed; monitor TSH every 4 weeks during pregnancy 3

Post-delivery: Reduce to pre-pregnancy dose immediately after delivery and recheck TSH 4-8 weeks postpartum 3