Levothyroxine is absorbed mainly in the small intestine, and absorption falls with food, coffee and many co-prescribed drugs. Calcium, iron, aluminium- and magnesium-containing antacids, sucralfate, bile acid sequestrants and phosphate binders bind it in the gut. Proton pump inhibitors may reduce absorption by raising gastric pH.
The usual advice is to take levothyroxine on an empty stomach, 30 to 60 minutes before breakfast or at bedtime well after the last meal, and to separate binding drugs by about four hours. A rising TSH in a previously stable patient should prompt a question about new medicines or supplements before the dose is increased.
- Take levothyroxine on an empty stomach, 30–60 minutes before breakfast or at bedtime.
- Separate calcium, iron, antacids and binders by about four hours.
- Ask about new supplements or acid suppressants when TSH rises unexpectedly.
- Keep timing consistent day to day rather than chasing a perfect schedule.
Why it matters
Absorption problems are a common cause of apparent dose failure.
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