Drug & supplement interaction

Magnesium + Alendronate

Alendronate brand names: Fosamax, Binosto.

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

Magnesium has a moderate interaction with Alendronate. Magnesium can decrease absorption of bisphosphonates.

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

Magnesium and Alendronate

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

Moderate

BISPHOSPHONATES

Why this applies to Alendronate

Alendronate falls under BISPHOSPHONATES — the group Magnesium interacts with.

Magnesium can decrease absorption of bisphosphonates.
Cations, including magnesium, can decrease bisphosphonate absorption. Advise patients to separate doses of magnesium and these drugs by at least 2 hours.
Severity Moderate Likelihood Probable Evidence B

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 practical issue with these two: magnesium can grab onto alendronate in your stomach and keep it from being absorbed. Alendronate is already very hard to absorb (only a tiny fraction gets in even on a good day), so anything that blocks it can leave you with little to no medicine actually working on your bones. Over time that could mean your osteoporosis treatment just isn't doing its job.

The fix is simple: spacing. Alendronate is meant to be taken first thing in the morning with plain water, then you stay upright and wait before eating, drinking, or taking anything else. Keep your magnesium (and other minerals like calcium or iron) at least a couple of hours away from your dose. If you're unsure how to time things, your pharmacist can map out a daily schedule with you.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Dunn CJ, Goa KL. Risedronate: a review of its pharmacological properties and clinical use in resorptive bone disease. Drugs 2001;61:685-712..

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

Magnesium Also Interacts With Other Medications

Magnesium has 6 major, 174 moderate, 114 minor known drug interactions in our database — the Alendronate one above is one of them. If you take anything else, check it against the full list below.

Major 6 Moderate 174 Minor 114 No known interaction 2,536 (incl. Alendronate)
Taking anything else?

Check Another of Your Medications Against Magnesium

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

From our Q&A

Questions About Magnesium or Alendronate

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Magnesium or Alendronate, 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 Alendronate

This page covers Magnesium only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Alendronate page lists 25 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Calcium (moderate), Coffee (moderate), Coffee Charcoal (moderate) and Dolomite (moderate).

By severity: 1 major · 15 moderate · 9 minor.

From our pharmacist’s overview on the Alendronate page

“Picture the typical Fosamax (alendronate) patient: someone taking a weekly tablet for thinning bones who also takes calcium and other mineral supplements, exactly what fills this list. Nearly all 25 ingredients on file work the same way, binding the drug in the gut or coating it with fiber so less gets absorbed, and a dose that never r…”

Reviewed by 2 · Jul 18, 2026

Open the Alendronate interaction page

One more smart check

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

We hold 29,718 real supplement products containing Magnesium, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Magnesium. Your product may carry other ingredients that interact with Alendronate too, on top of Magnesium — 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 Magnesium and Alendronate 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 Magnesium
Top 10

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

29 days ago today
Medication Alendronate
Top 25%

#501 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 Magnesium

What is Magnesium?

Magnesium
  • Preventing or treating magnesium deficiency
  • Constipation
  • Muscle cramps
  • Sleep support
  • Anxiety and stress
  • Migraine prevention

Magnesium is an essential mineral your body needs for muscles, nerves, blood pressure, and many other functions, and supplements are useful for preventing or correcting deficiency. Some other uses, like easing constipation or preventing migraines, have reasonable support, while uses for sleep and anxiety are less proven. It is generally safe for most healthy people at recommended amounts, but talk to your pharmacist or doctor before starting, especially if you have kidney problems.

Read the full Magnesium monograph & all interactions
Medication

About Alendronate

What Is Alendronate Used For?

Brand names: Fosamax, Binosto

Alendronate slows bone breakdown. It is used mainly for osteoporosis (thin, fragile bones that break more easily).

Uses differ by product. Alendronate tablets and Fosamax tablets are used for osteoporosis in postmenopausal women (treatment and prevention) and in men. They are also used for glucocorticoid-induced osteoporosis and Paget's disease of bone. Alendronate sodium oral solution and Binosto effervescent tablets are used only to treat osteoporosis in postmenopausal women and to increase bone mass in men with osteoporosis.

See full Alendronate drug information
Keep checking

Other Drugs & Magnesium

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

6Major
174Moderate
114Minor
2,535No known interaction
6 Major 174 Moderate 114 Minor 2,535 No interaction
Major

6 interactions

Moderate

174 interactions

Showing 60 of 174 moderate interactions — see all 174 on the Magnesium page.

Minor

114 interactions

Showing 60 of 114 minor interactions — see all 114 on the Magnesium page.

No interaction 2,535 drugs checked — show the list

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

Showing the 60 most looked-up of 2,535 medications checked with no known interaction — see the full Magnesium list.

See the full Magnesium interactions page
See every supplement checked against Alendronate, 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
Magnesium monograph › Uses, safety, and every drug interaction in one place Alendronate supplement interactions › Every supplement checked against Alendronate, ranked by severity Alendronate drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Magnesium and Alendronate Together: Common Questions

Can you take Magnesium with Alendronate?
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 Magnesium and Alendronate 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 Alendronate and Magnesium?

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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.