Drug & supplement interaction

Calcium + Doxycycline monohydrate

Doxycycline monohydrate brand name: Erfacea.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Calcium has a moderate interaction with Doxycycline monohydrate. Calcium seems to reduce the absorption of tetracycline antibiotics.

Read the full interaction report
SeverityModerate
LikelihoodProbable
EvidenceC
What do Severity, Likelihood & Evidence mean?
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Interaction report

Calcium and Doxycycline monohydrate

Here is the interaction we found between these two, with the evidence behind it.

Moderate

TETRACYCLINE ANTIBIOTICS

Why this applies to Doxycycline monohydrate

Doxycycline monohydrate falls under TETRACYCLINE ANTIBIOTICS — the group Calcium interacts with.

Calcium seems to reduce the absorption of tetracycline antibiotics.
Advise patients to take oral tetracyclines at least 2 hours before, or 4-6 hours after calcium supplements. Taking calcium at the same time as oral tetracyclines can reduce tetracycline absorption. Calcium binds to tetracyclines in the gut.
Severity Moderate Likelihood Probable Evidence C

Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the simple version: when calcium and doxycycline meet in your stomach, the calcium grabs onto the antibiotic and forms a clump your gut can't absorb well. The result is that less doxycycline gets into your bloodstream, so it may not fight your infection as strongly as it should. That's the worry here, not extra side effects, but a weaker antibiotic.

The good news is this is easy to manage with timing. A common approach is to take your doxycycline at least 2 hours before or 4 to 6 hours after any calcium supplement. The same idea applies to calcium-rich dairy, antacids with calcium, and many vitamin combos. Check with your pharmacist about the best schedule for you so your antibiotic does its job.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Maton PN, Burton ME. Antacids revisited: a review of their clinical pharmacology and recommended therapeutic use. Drugs 1999;57:855-70.

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Calcium Also Interacts With Other Medications

Calcium has 7 major, 142 moderate, 18 minor known drug interactions in our database — the Doxycycline monohydrate one above is one of them. If you take anything else, check it against the full list below.

Major 7 Moderate 142 Minor 18 No known interaction 2,663 (incl. Doxycycline monohydrate)
Taking anything else?

Check Another of Your Medications Against Calcium

Covers the 2,830 medications we’ve checked against Calcium. Pick one to open its full report.

From our Q&A

Questions About Calcium or Doxycycline monohydrate

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Calcium or Doxycycline monohydrate, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Doxycycline monohydrate

This page covers Calcium only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Doxycycline monohydrate page lists 166 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Asarabacca (major), Beer (major), Oleander (major) and Siberian Cocklebur (major).

Open the Doxycycline monohydrate interaction page

One more smart check

Taking Calcium as Part of a Dietary Supplement Product? Check It for Interactions

We hold 38,397 real supplement products containing Calcium, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Calcium. Your product may carry other ingredients that interact with Doxycycline monohydrate too, on top of Calcium — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Calcium and Doxycycline monohydrate Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Calcium
Top 10

#2 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Doxycycline monohydrate
Top half

#1,177 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Calcium

What is Calcium?

  • Bone health and osteoporosis prevention
  • Dietary calcium deficiency
  • Heartburn relief (calcium carbonate antacids)
  • Supporting healthy teeth
  • High blood pressure support during pregnancy

Calcium is an essential mineral your body needs for strong bones, nerve signaling, and muscle function, and supplements can help fill gaps when diet falls short. Most people do best getting calcium from food, and supplements should be used at the lowest dose needed. Talk to your pharmacist or doctor before starting, especially if you have kidney problems or take other medicines.

Read the full Calcium monograph & all interactions
Keep checking

Other Drugs & Calcium

Browse every other medication we’ve checked against Calcium — both the ones with a known interaction and the ones without. Select any drug for the full detail.

7Major
142Moderate
18Minor
2,662No known interaction
7 Major 142 Moderate 18 Minor 2,662 No interaction
Major

7 interactions

Moderate

142 interactions

Showing 60 of 142 moderate interactions — see all 142 on the Calcium page.

Minor

18 interactions

No interaction 2,662 drugs checked — show the list

We also checked Calcium against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,662 medications checked with no known interaction — see the full Calcium list.

See the full Calcium interactions page
See every supplement checked against Doxycycline monohydrate, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
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Pharmacist Counseling Corner

Taking Calcium and Doxycycline monohydrate Together: Common Questions

Can you take Calcium with Doxycycline monohydrate?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Calcium and Doxycycline monohydrate interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Doxycycline monohydrate and Calcium?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.