NutriStack
Calcium Carbonate and Doxycycline, timing-sensitive.
Calcium carbonate, taken as either an antacid or calcium supplement, chelates doxycycline in the gut and reduces its absorption substantially. The chelate complex is essentially nonabsorbable. Lower doxycycline levels can cause treatment failure.
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At a glance
- Substances
- Calcium Carbonate and Doxycycline
- Pair type
- Timing Sensitive
- Evidence (highest tier)
- Strong
- Source citations
- 2 sources
- Stack Score effect
- −5 to your Stack Score (per scored timing-sensitive row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Timing Sensitive · Strong evidence
Timing Sensitive
What is happening. Calcium carbonate, taken as either an antacid or calcium supplement, chelates doxycycline in the gut and reduces its absorption substantially. The chelate complex is essentially nonabsorbable. Lower doxycycline levels can cause treatment failure.
Mechanism. Ca2+ chelates the beta-diketone system of tetracyclines, forming insoluble complexes that block intestinal absorption.
Recommendation. Take doxycycline at least 2 hours before or 6 hours after calcium carbonate. Do not co-administer.
Minimum separation. 360
Sources (2)
- Gugler R, Allgayer H. Effects of antacids on the clinical pharmacokinetics of drugs. An update. Clin Pharmacokinet. 1990;18(3):210-219. PMID 1969784
- Eljaaly K, Helal A, Almandeel T, Algarni R, Alshehri S. Multivalent cations interactions with fluoroquinolones or tetracyclines: A cross-sectional study. Saudi J Biol Sci. 2021;28(12):6929-6932. PMID 34866992
Stack Score
How this pair moves the number.
Effect on the composite score
If both Calcium Carbonate and Doxycycline are in the same stack, this pair applies −5 to your Stack Score (per scored timing-sensitive row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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