What Is Levothyroxine and How Does It Work?

Q: What Is Levothyroxine and How Does It Work?

Levothyroxine is synthetic T4 — the standard treatment for hypothyroidism. Take on empty stomach. TSH checked 6-8 weeks after dose changes.

Levothyroxine is synthetic T4 — the most prescribed treatment for hypothyroidism worldwide.

How It Works

Replaces the T4 your thyroid cannot produce
Body converts T4 to active T3 in tissues
Normalizes metabolism

How to Take

Once daily, same time
Empty stomach: 30–60 min before breakfast
Water only
Separate from calcium/iron by 4 hours

Dosing

Starting: 1.6 µg/kg/day
TSH checked 6–8 weeks after change
Adjusted until TSH normal

Drug Interactions

Calcium, iron, antacids reduce absorption
Coffee reduces absorption
Soy reduces absorption

Source: American Thyroid Association, NLM MedlinePlus.

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