Drug & supplement interaction

Phosphate Salts + Alendronate Sodium, Cholecalciferol

Alendronate Sodium, Cholecalciferol brand name: Fosamax Plus D.

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

Phosphate Salts has a moderate interaction with Alendronate Sodium, Cholecalciferol. Theoretically, taking phosphate salts with bisphosphonates might increase the risk of hypocalcemia.

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

Phosphate Salts and Alendronate Sodium, Cholecalciferol

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

Moderate

BISPHOSPHONATES

Why this applies to Alendronate Sodium, Cholecalciferol

Alendronate Sodium, Cholecalciferol falls under BISPHOSPHONATES — the group Phosphate Salts interacts with.

Theoretically, taking phosphate salts with bisphosphonates might increase the risk of hypocalcemia.
Combining bisphosphonates and phosphate can cause hypocalcemia. In one report, hypocalcemic tetany developed in a patient taking alendronate (Fosamax) who received a large dose of phosphate salts as a pre-operative laxative.
Severity Moderate Likelihood Possible Evidence D

Interaction 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.

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

Here's the simple version. Your Fosamax Plus D contains alendronate, a bisphosphonate that works to strengthen bone. One of the things it can do is lower your blood calcium a bit. Phosphate salts can also pull calcium down. Put the two together and, in theory, your calcium could dip lower than it should.

I want to be honest about how strong this concern is: it rests mostly on a single case report, where someone on alendronate took a large dose of phosphate as a pre-surgery laxative and developed low-calcium symptoms (muscle cramping and spasms, tingling around the mouth or fingers). For everyday dietary phosphorus, this really isn't a worry. The caution is about concentrated phosphate supplements or laxatives. Before combining them, please check with your pharmacist or doctor first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Campisi P, Badhwar V, Morin S, Trudel JL. Postoperative hypocalcemic tetany caused by Fleet Phospho-Soda preparation in a patient taking alendronate sodium. Dis Colon Rectum 1999;42:1499-501. DOI

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

Phosphate Salts Also Interacts With Other Medications

Phosphate Salts has 2 major, 9 moderate known drug interactions in our database — the Alendronate Sodium, Cholecalciferol one above is one of them. If you take anything else, check it against the full list below.

Major 2 Moderate 9 No known interaction 2,819 (incl. Alendronate Sodium, Cholecalciferol)
Taking anything else?

Check Another of Your Medications Against Phosphate Salts

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

Everything else you take

See Every Supplement That Interacts With Alendronate Sodium, Cholecalciferol

This page covers Phosphate Salts only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Alendronate Sodium, Cholecalciferol 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 Sodium, Cholecalciferol page

“Activated charcoal carries the only major rating against Fosamax Plus D (alendronate with cholecalciferol), and it deserves real respect from anyone taking this bone medicine. Charcoal soaks up drugs in the gut, so less alendronate ever reaches the skeleton it is supposed to strengthen.”

Reviewed by 2 · Jul 18, 2026

Open the Alendronate Sodium, Cholecalciferol interaction page

One more smart check

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

We hold 6 real supplement products containing Phosphate Salts, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Phosphate Salts. Your product may carry other ingredients that interact with Alendronate Sodium, Cholecalciferol too, on top of Phosphate Salts — 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 Phosphate Salts and Alendronate Sodium, Cholecalciferol 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 Phosphate Salts
Steady interest

#1,041 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Alendronate Sodium, Cholecalciferol
Steady interest

#2,482 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 Phosphate Salts

What is Phosphate Salts?

  • Low blood phosphate levels (hypophosphatemia)
  • Bowel preparation/laxative use
  • Athletic performance ('phosphate loading')
  • Preventing certain kidney stones
  • Calcium supplementation balance

Phosphate salts are mineral compounds used mainly to correct low phosphate levels, as laxatives, and sometimes by athletes. Most people who eat a normal diet already get plenty of phosphate and do not need a supplement. Because too much phosphate can be dangerous—especially for people with kidney disease—use these products only under the guidance of a doctor or pharmacist.

Read the full Phosphate Salts monograph & all interactions
Keep checking

Other Drugs & Phosphate Salts

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

2Major
9Moderate
0Minor
2,818No known interaction
2 Major 9 Moderate 2,818 No interaction
Major

2 interactions

Moderate

9 interactions

No interaction 2,818 drugs checked — show the list

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

Showing the 60 most looked-up of 2,818 medications checked with no known interaction — see the full Phosphate Salts list.

See the full Phosphate Salts interactions page
See every supplement checked against Alendronate Sodium, Cholecalciferol, 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
Phosphate Salts monograph › Uses, safety, and every drug interaction in one place Alendronate Sodium, Cholecalciferol supplement interactions › Every supplement checked against Alendronate Sodium, Cholecalciferol, ranked by severity 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 Phosphate Salts and Alendronate Sodium, Cholecalciferol Together: Common Questions

Can you take Phosphate Salts with Alendronate Sodium, Cholecalciferol?
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 Phosphate Salts and Alendronate Sodium, Cholecalciferol 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 Sodium, Cholecalciferol and Phosphate Salts?

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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.