Calcium citrate and Levothyroxine: interaction, severity and spacing
Calcium citrate and Levothyroxine interact because calcium binds levothyroxine in the intestinal lumen, reducing absorption by up to a third. Take them 4 hours apart. Severe risk.
The interaction in detail
| Pair | Calcium citrate and Levothyroxine |
|---|---|
| Type | Nutrient–drug interaction |
| Severity | Severe |
| Required spacing | 4 hours minimum |
| Onset | At the time of dosing |
Mechanism
Calcium binds levothyroxine in the intestinal lumen, reducing absorption by up to a third.
What to do
Separate calcium from levothyroxine by at least 4 hours. Keep the timing the same every day.
How to fit both into one day
Calcium absorbs better with food and in doses at or below 500 mg. Take it with vitamin D3, and separate it from iron, zinc and thyroid medication.
Levothyroxine needs an empty stomach and gastric acid for full absorption. Take it 30-60 minutes before breakfast with plain water, and keep calcium, iron and coffee at least 4 hours away.
Putting Calcium citrate in the midday and Levothyroxine in the morning satisfies the 4-hour separation without disrupting either one's absorption window.