Calcium and Levothyroxine
Supplement–drug interaction evidence from the TruthStack database.
| Severity | HIGH |
|---|---|
| Evidence Tier | Moderate |
| Interaction Type | ABSORPTION INTERFERENCE |
| Mechanism | CHELATION |
| Last Reviewed | 2026-02-15 |
Summary
Calcium chelates levothyroxine in GI tract reducing absorption by up to 50 percent. Can cause hypothyroid symptoms even on correct dose. Consider separating doses by at least 4 hours. Consider taking levothyroxine on empty stomach, calcium with meals later in day.
API Reference
GET https://api.truthstack.co/v1/check?c1=calcium&c2=levothyroxine
Open, unauthenticated. Returns JSON. Developer documentation
Related Interactions
What this page is and is not. TruthStack is an informational reference database that describes published pharmacological findings. It does not provide medical advice, diagnosis, or treatment recommendations. The information on this page reflects flags in our database and should not replace consultation with a qualified healthcare provider. Always discuss supplement-drug combinations with your prescriber or pharmacist.