Use TSH as the main test for dose adjustment in primary hypothyroidism
Check free T4 when TSH is unreliable or in central hypothyroidism
Recheck labs 6 to 8 weeks after any dose change
Adjust dose in small steps, usually 12.5 to 25 mcg at a time
Increase dose if TSH is above target and symptoms suggest under-replacement
Decrease dose if TSH is below target or symptoms suggest over-replacement
Aim for a normal TSH range unless a different target is needed
Use a lower starting dose in older adults, heart disease, or frailty
Use a higher dose requirement in pregnancy, obesity, malabsorption, or after thyroid removal
Take levothyroxine on an empty stomach at the same time daily
Separate levothyroxine from calcium, iron, antacids, and certain supplements by at least 4 hours
Review adherence before changing the dose
Review interacting medications before changing the dose
Consider weight change, pregnancy, illness, and brand changes when reassessing dose
Monitor more closely after starting or stopping estrogen, amiodarone, anticonvulsants, or rifampin
In thyroid cancer patients, follow the prescribed TSH suppression target
Avoid using symptoms alone to decide dose without lab confirmation
Keep the same formulation when possible for consistent dosing
Recheck sooner if symptoms are severe, pregnancy is present, or major medication changes occur