What is the primary treatment for a patient with hypothyroidism?

Primary Treatment for Hypothyroidism

Levothyroxine sodium monotherapy is the primary treatment for all patients with hypothyroidism, serving as first-line therapy for primary, secondary, and tertiary hypothyroidism. 1, 2, 3

Core Treatment Principles

Levothyroxine (T4) is the standard of care and should be used as replacement therapy in all forms of hypothyroidism—whether primary (thyroidal), secondary (pituitary), or tertiary (hypothalamic), in both congenital and acquired cases 1, 3. This medication has been the cornerstone of hypothyroidism treatment for decades and is one of the world's most widely prescribed medicines 4.

Initial Dosing Strategy

For Most Adult Patients (<70 years, no cardiac disease)

• Start with full replacement dose of approximately 1.6 mcg/kg/day 1, 4
• This approach rapidly normalizes thyroid function and prevents complications 1

For High-Risk Patients (>70 years OR cardiac disease)

• Start with 25-50 mcg/day and titrate gradually 1, 2, 5
• Elderly patients and those with coronary artery disease or atrial fibrillation require lower starting doses to avoid unmasking cardiac ischemia or precipitating arrhythmias 5, 6
• Patients with long-standing severe hypothyroidism also require conservative initiation 6

Treatment Targets and Monitoring

Target TSH: 0.4-4.5 mIU/L (some sources cite 0.5-4.5 mIU/L) 1, 6, 4, 7

Monitoring Schedule:

• Check TSH every 6-8 weeks after initiating therapy or changing doses 1, 5
• Once TSH reaches target range, monitor annually 1, 5
• Free T4 can help interpret ongoing abnormal TSH levels during therapy, as TSH may take longer to normalize 1

Critical Safety Considerations

Rule Out Adrenal Insufficiency First

In patients with suspected central (secondary/tertiary) hypothyroidism, always evaluate and treat adrenal insufficiency BEFORE starting levothyroxine 1. Starting thyroid hormone before corticosteroids can precipitate life-threatening adrenal crisis 1. This is particularly important in patients with pituitary disease or those on immune checkpoint inhibitors 1.

Pregnancy Considerations

• All pregnant women or women planning pregnancy with any TSH elevation should be treated immediately 1, 2, 6
• Target TSH <2.5 mIU/L in first trimester 1
• Monitor TSH every 6-8 weeks during pregnancy as requirements often increase by 25-50% 1, 2
• Untreated hypothyroidism increases risk of preeclampsia, low birth weight, and impaired fetal neurodevelopment 2, 5

Absolute Indications for Treatment

Treat immediately in these scenarios:

• TSH >10 mIU/L regardless of symptoms 1, 6
• Any TSH elevation with low free T4 (overt hypothyroidism) 1, 5
• Symptomatic patients with any degree of TSH elevation 1
• Pregnant women or women planning pregnancy with any TSH elevation 1, 2, 6

Subclinical Hypothyroidism (TSH 4.5-10 mIU/L with normal free T4)

Consider treatment in:

• Symptomatic patients (fatigue, weight gain, cold intolerance, cognitive issues) 1, 6
• Patients with positive anti-TPO antibodies (4.3% annual progression risk vs 2.6% without antibodies) 1, 6
• Patients with infertility or goiter 6

Do NOT routinely treat asymptomatic patients with TSH 4.5-10 mIU/L—instead monitor thyroid function every 6-12 months 1

Common Pitfalls to Avoid

Overtreatment

• Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH 1
• TSH suppression (<0.1 mIU/L) increases risk for atrial fibrillation (3-5 fold), osteoporosis, fractures, and cardiovascular mortality 1, 6
• If TSH <0.1 mIU/L: reduce dose by 25-50 mcg immediately 1
• If TSH 0.1-0.45 mIU/L: reduce dose by 12.5-25 mcg, especially in elderly or cardiac patients 1

Undertreatment

• Persistent hypothyroid symptoms, adverse cardiovascular effects, abnormal lipid metabolism, and reduced quality of life 1
• Increased risk of heart failure and cardiovascular events 5, 4

Treating Without Confirmation

• 30-60% of elevated TSH levels normalize spontaneously on repeat testing 1
• Always confirm elevated TSH with repeat testing after 3-6 weeks before initiating treatment 1

Consequences of Untreated Hypothyroidism

Untreated hypothyroidism can lead to serious complications including:

• Heart failure and cardiovascular disease 2, 5, 4
• Myxedema coma (mortality rate up to 30%) 2, 5
• In pregnancy: preeclampsia, congenital cretinism, low birth weight, impaired fetal cognitive development 2, 5, 6
• Insulin resistance and hyperglycemia in diabetic patients 5
• Infertility and increased miscarriage risk 5

Administration Guidelines

• Take levothyroxine on an empty stomach, 30-60 minutes before breakfast 1
• Separate from iron, calcium supplements, or antacids by at least 4 hours 1
• Consistent timing and administration method ensures optimal absorption 8