What is the primary treatment for hypothyroidism?

Primary Treatment for Hypothyroidism

Levothyroxine (synthetic T4) is the first-line treatment for hypothyroidism, with dosing tailored to the specific type of hypothyroidism and patient characteristics. 1, 2

Types of Hypothyroidism and Initial Treatment Approach

Primary Hypothyroidism (Most Common)

• Initial dosing: 1.6 mcg/kg/day for adults under 70 without cardiac disease 3
• Target TSH range: 0.5-2.0 mIU/L 3

Central Hypothyroidism (Secondary/Tertiary)

• Initial dosing: 1 mcg/kg levothyroxine 3
• Critical safety note: Ensure cortisol replacement is initiated 1 week before starting thyroid hormone to prevent adrenal crisis 3
• Monitor free T4 rather than TSH, targeting the upper half of the normal range 3

Special Populations

• Elderly patients or those with cardiac conditions:
  • Start with lower dose: 25-50 mcg/day 3
  • Target TSH range: 1.0-4.0 mIU/L 3
• Pregnant women:
  • Adjust dose to restore TSH to reference range (0.5-2.0 mIU/L) 3
  • Monitor TSH regularly as requirements may increase during pregnancy 1

Monitoring and Dose Adjustments

• Primary hypothyroidism: Monitor TSH and free T4 levels

  • Check 6-8 weeks after initiating treatment or changing dose 2
  • Once stable, monitor every 6-12 months 3

• Central hypothyroidism: Monitor free T4 only (not TSH)

  • Follow-up every 3 months during first year 3
  • Then every 6-12 months once stable 3

Potential Complications and Pitfalls

Undertreatment

• Persistent symptoms: fatigue, weight gain, cognitive issues, menstrual irregularities 2
• Increased cardiovascular risk 2, 4
• Metabolic effects: insulin resistance, hyperglycemia in diabetic patients 2

Overtreatment

• Increased risk of atrial fibrillation (3-fold increased risk in adults ≥60 years with TSH ≤0.1 mIU/L) 3
• Increased all-cause mortality (up to 2.2-fold) and cardiovascular mortality (up to 3-fold) in individuals >60 years with TSH <0.5 mIU/L 3
• Osteoporosis risk, especially in elderly patients 3

Important Administration Considerations

• Take levothyroxine on an empty stomach, 30-60 minutes before breakfast or 3-4 hours after the last meal of the day
• Avoid taking with medications that can interfere with absorption (calcium, iron supplements, proton pump inhibitors)
• Maintain consistent timing of administration to ensure stable hormone levels

Clinical Pearls

• Nearly one-third of patients with treated hypothyroidism still exhibit symptoms despite normalized TSH levels 5
• Some patients may benefit from combination therapy with levothyroxine plus liothyronine (T3), though this remains an area of ongoing research 5, 6
• Bioequivalence can differ among generic and brand name levothyroxine products 6
• Avoid abrupt discontinuation of treatment, especially in patients with long-standing hypothyroidism

Levothyroxine is one of the most widely prescribed medications worldwide, and proper dosing and monitoring are essential to achieve optimal outcomes and avoid complications related to both under- and over-treatment 2, 5.