Increase Levothyroxine Dose by 12.5-25 mcg and Recheck TSH in 6-8 Weeks
If your TSH remains elevated on Synthroid 200 mcg, you need a dose increase—this indicates inadequate thyroid hormone replacement that requires prompt adjustment. 1, 2
Immediate Assessment Before Dose Adjustment
Before increasing your dose, verify these critical factors that can falsely elevate TSH or impair levothyroxine absorption:
- Confirm medication adherence: Take levothyroxine on an empty stomach, 30-60 minutes before breakfast, and avoid taking it with iron, calcium supplements, or proton pump inhibitors within 4 hours 1
- Rule out malabsorption: Conditions like celiac disease, inflammatory bowel disease, or gastric bypass surgery can impair levothyroxine absorption 1
- Check for drug interactions: Enzyme inducers (phenytoin, carbamazepine, rifampin) increase levothyroxine metabolism and may require higher doses 1
- Exclude recent iodine exposure: CT contrast or amiodarone can transiently affect thyroid function tests 1
Recommended Dose Adjustment Strategy
Increase levothyroxine by 12.5-25 mcg based on your age and cardiac status 1, 2:
- For patients under 70 years without cardiac disease: Increase by 25 mcg to reach 225 mcg daily 1, 2
- For patients over 70 years or with cardiac disease/atrial fibrillation: Use smaller 12.5 mcg increments to minimize cardiac complications 1, 2
The specific increment depends on how elevated your TSH is:
- TSH 4.5-10 mIU/L: Consider 12.5 mcg increase, especially if asymptomatic 1, 2
- TSH >10 mIU/L: Use 25 mcg increase regardless of symptoms, as this level carries approximately 5% annual risk of progression to overt hypothyroidism 1, 3
Monitoring Timeline After Dose Adjustment
Recheck TSH and free T4 in exactly 6-8 weeks after any dose change—this represents the time needed to reach steady state 1, 2. Testing earlier or later than this window provides unreliable results 1.
- Target TSH range: 0.5-4.5 mIU/L with normal free T4 1, 2
- Once stable: Monitor TSH annually or sooner if symptoms change 1
- For patients with cardiac disease or atrial fibrillation: Consider repeating testing within 2 weeks if symptoms develop 1
Critical Pitfalls to Avoid
Never make excessive dose increases (jumping from 200 mcg to 250 mcg or higher), as this risks iatrogenic hyperthyroidism, which occurs in 14-21% of treated patients and increases risk for atrial fibrillation, osteoporosis, and cardiac complications 1, 3. Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH 1.
Do not adjust doses more frequently than every 6-8 weeks—levothyroxine has a long half-life and requires this interval to reach steady state 1, 4.
If TSH remains elevated despite confirmed adherence and adequate dosing, consider:
- Measuring anti-TPO antibodies if not already done—positive antibodies indicate autoimmune thyroiditis (Hashimoto's) with 4.3% annual progression risk to overt hypothyroidism versus 2.6% in antibody-negative patients 1
- Evaluating for central hypothyroidism if TSH is inappropriately normal or low with low free T4—this requires checking other pituitary hormones and treating adrenal insufficiency before increasing thyroid hormone 1
Special Considerations
For elderly patients with coronary disease: Even therapeutic levothyroxine doses can unmask or worsen cardiac ischemia, so use conservative 12.5 mcg increments and monitor closely for angina or arrhythmias 1.
If you have thyroid cancer: Your target TSH may be intentionally lower (0.1-0.5 mIU/L for intermediate-risk patients, <0.1 mIU/L for high-risk patients), so consult your endocrinologist before adjusting doses 1, 2.
Pregnancy considerations: If planning pregnancy, more aggressive TSH normalization is warranted as subclinical hypothyroidism is associated with preeclampsia, low birth weight, and neurodevelopmental effects in offspring 1.