When do you adjust thyroid medication in patients with hypothyroidism, such as those taking levothyroxine (T4) or liothyronine (T3), based on their thyroid-stimulating hormone (TSH) levels and symptoms?

When to Adjust Thyroid Medication in Hypothyroidism

Adjust levothyroxine dose when TSH falls outside the target range of 0.5-4.5 mIU/L after 6-8 weeks on a stable dose, or when symptoms change despite biochemical euthyroidism. 1

Initial Monitoring During Dose Titration

Check TSH every 6-8 weeks after starting levothyroxine or changing the dose, as this represents the time needed to reach steady state. 1, 2 This interval is critical because levothyroxine has a long half-life, and adjusting doses more frequently leads to overcorrection and iatrogenic complications. 1

• For pediatric patients, monitor TSH and free T4 at 2 and 4 weeks after initiation, 2 weeks after any dose change, then every 3-12 months after stabilization. 2
• For pregnant patients with pre-existing hypothyroidism, check TSH every 4 weeks until stable, then at minimum once per trimester. 1, 2
• For patients with cardiac disease or atrial fibrillation, consider repeating testing within 2 weeks rather than waiting 6-8 weeks if clinically indicated. 1

Long-Term Monitoring After Stabilization

Once TSH is within target range on a stable dose, recheck TSH every 6-12 months. 1, 2 This applies to patients who are asymptomatic and have no changes in clinical status. 1

• Recheck sooner if symptoms develop, such as fatigue, weight changes, palpitations, or other signs of hypo- or hyperthyroidism. 1
• Recheck if medications change that affect levothyroxine absorption (iron, calcium, antacids) or metabolism (enzyme inducers). 3

Specific Scenarios Requiring Dose Adjustment

TSH Above Target Range (>4.5 mIU/L)

Increase levothyroxine by 12.5-25 mcg based on current dose and patient characteristics. 1

• For TSH >10 mIU/L, increase dose regardless of symptoms, as this carries ~5% annual risk of progression to overt hypothyroidism. 1
• For TSH 4.5-10 mIU/L in patients already on treatment, dose adjustment is reasonable to normalize TSH into the reference range. 1
• Use 25 mcg increments for patients <70 years without cardiac disease. 1
• Use 12.5 mcg increments for elderly patients (>70 years) or those with cardiac disease to avoid cardiac complications. 1

After adjustment, recheck TSH in 6-8 weeks. 1, 2

TSH Below Target Range (<0.5 mIU/L)

Reduce levothyroxine dose to prevent complications of iatrogenic hyperthyroidism. 1

• For TSH 0.1-0.45 mIU/L, decrease dose by 12.5-25 mcg, particularly if in the lower part of this range or in patients with atrial fibrillation, cardiac disease, or elderly with risk factors. 1
• For TSH <0.1 mIU/L, decrease dose by 25-50 mcg immediately, as prolonged suppression significantly increases risk of atrial fibrillation, osteoporosis, and cardiovascular mortality. 1

Exception: Patients with thyroid cancer may require intentional TSH suppression—consult with endocrinologist before adjusting. 1 Target TSH varies by risk stratification: 0.5-2 mIU/L for low-risk patients, 0.1-0.5 mIU/L for intermediate-risk, and <0.1 mIU/L for structural incomplete response. 1

After reduction, recheck TSH in 6-8 weeks. 1

Common Pitfalls to Avoid

Do not adjust doses based on symptoms alone when TSH is within target range (0.5-4.5 mIU/L). 1 Persistent symptoms despite normal TSH often reflect other comorbidities, not inadequate thyroid replacement. 4, 5

Do not adjust doses more frequently than every 6-8 weeks, as this leads to overcorrection before steady state is reached. 1, 3

Approximately 25% of patients are unintentionally maintained on doses that fully suppress TSH, increasing risks for atrial fibrillation, osteoporosis, fractures, and cardiac complications. 1 Regular monitoring prevents this.

Never start or increase levothyroxine without ruling out adrenal insufficiency in patients with suspected central hypothyroidism, as this can precipitate adrenal crisis. 1

Special Populations

Elderly Patients

Target TSH may be slightly higher in elderly patients, as the normal reference range shifts upward with age. 1 The 97.5th percentile is 7.5 mIU/L for patients over age 80 compared to 3.6 mIU/L for those under 40. 4

Pregnant Patients

Levothyroxine requirements typically increase 25-50% during pregnancy. 1 Increase dose by 12.5-25 mcg per day when TSH rises above trimester-specific reference range, monitoring every 4 weeks. 2 Reduce to pre-pregnancy dose immediately after delivery and recheck TSH 4-8 weeks postpartum. 2

Patients on Immunotherapy

Monitor TSH every 4-6 weeks for the first 3 months, then every second cycle in patients on immune checkpoint inhibitors. 1 Consider treatment even for subclinical hypothyroidism if fatigue or other symptoms are present. 1