Supplements and Alendronic acid.
Alendronic acid, sold under the brand names Fosamax, Fosavance, Binosto, is a bisphosphonate. Oral absorption is reduced by polyvalent cations including calcium, magnesium and iron.
Alendronic acid is a bisphosphonate. UK prescribing is mostly for osteoporosis or to reduce skeletal complications of certain cancers. Oral bisphosphonates have notoriously low bioavailability at around 1 percent. Absorption is reduced to near zero by polyvalent cations. Calcium, magnesium, and iron supplements need a strict two hour separation, sometimes longer per the guidance for a specific product. The MHRA-flagged side effects are oesophagitis (mitigated by taking the dose with a full glass of water, remaining upright for 30 to 60 minutes, and not eating until after that window), atypical femoral fractures with use over many years, and osteonecrosis of the jaw. Vitamin D and calcium adequacy underpin bisphosphonate efficacy. A deficient patient gets less benefit. Confirming vitamin D status on a blood test before starting is sensible. The timing and separation rule with supplements is the most common compliance failure point.
Below are the 8 documented pairs we have explicitly assessed against Alendronic acid in the Distil database: 7 amber and 1 green. The pairs cluster around 2 mechanisms: Mineral chelation (absorption) and Beneficial combination. Every call is cited to either a clinical reference (PMID) or the British National Formulary. Anything not on this list is either still to be assessed or beyond our database scope. The checker beneath surfaces assessments by supplement, and the missing-item form at the bottom of the page routes any uncatalogued supplement into our next curation pass.
Documented interactions
Last reviewed 13 June 2026. Each interaction below lists the evidence its assessment drew on: some rest on studies of the exact pair, others on mechanism evidence, where a citation may support one part of the reasoning rather than the exact combination. The evidence line on each entry says which.
Mineral chelation (absorption)
Amber Does Calcium interact with ?
Calcium binds to alendronic acid in the gut and almost completely blocks how much you absorb. Take alendronic acid first thing in the morning with plain water on an empty stomach, stay upright for 30 minutes, then wait at least two hours before any calcium-containing food, drink or supplement.
Evidence: Supported by human study data.
Amber Does Iron interact with ?
Iron binds to alendronic acid in the gut and blocks absorption in the same way calcium does. Take alendronic acid first thing on an empty stomach with plain water, stay upright for 30 minutes, then wait at least two hours before any iron supplement.
Evidence: Supported by human study data.
Amber Does Magnesium interact with ?
Magnesium binds to alendronic acid in the gut and blocks absorption in the same way calcium does. Take alendronic acid first thing on an empty stomach with plain water, stay upright for 30 minutes, then wait at least two hours before any magnesium supplement.
Evidence: Supported by human study data.
Amber Does Magnesium Glycinate interact with ?
Magnesium binds to alendronic acid in the gut and blocks absorption in the same way calcium does. Take alendronic acid first thing on an empty stomach with plain water, stay upright for 30 minutes, then wait at least two hours before any magnesium supplement.
Evidence: Supported by human study data.
Amber Does Magnesium L-Threonate interact with ?
Magnesium binds to alendronic acid in the gut and blocks absorption, the same way calcium does. Magnesium L-threonate is still elemental magnesium, so it has the same effect. Take alendronic acid first thing on an empty stomach with plain water, stay upright for 30 minutes, then wait at least two hours before any magnesium supplement.
Evidence: Supported by human study data.
Amber Does Zinc interact with ?
Zinc is a divalent metal that can bind to alendronic acid in the gut and reduce how much you absorb, the same way calcium and iron do. Take alendronic acid first thing in the morning with plain water on an empty stomach, stay upright for 30 minutes, then separate any zinc supplement by at least two hours.
Evidence: Based on an established mechanism, with no direct study of this exact combination yet.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Amber Does Zinc Bisglycinate interact with ?
Zinc is a divalent metal that can bind to alendronic acid in the gut and reduce how much you absorb, the same way calcium and iron do. Take alendronic acid first thing in the morning with plain water on an empty stomach, stay upright for 30 minutes, then separate any zinc supplement by at least two hours.
Evidence: Based on an established mechanism, with no direct study of this exact combination yet.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Beneficial combination
Green Does Vitamin D3 interact with ?
Vitamin D and alendronic acid are expected to be taken together. Adequate vitamin D is recommended alongside a bisphosphonate like alendronic acid: it helps keep your blood calcium in a healthy range and supports the medicine working as intended. The one practical point is timing, not safety. Alendronic acid must be taken first thing on an empty stomach with plain water, staying upright for 30 minutes, so take any vitamin D product (especially a combined vitamin D plus calcium supplement) later in the day. If your vitamin D is very low, your GP may want to correct it before or as you start, so ask them to confirm your levels.
Evidence: Supported by human study data.
What this list does not say. Pairs not flagged here are not implicitly safe. They are either not yet in our database, or fall outside our inclusion scope (food-supplement interactions only; for drug-drug interactions, the BNF is authoritative). Use the checker below to surface any supplement, and submit a missing item if you take something we have not catalogued.
No affiliates. No commission. We earn nothing on what you buy.
How we grade severity, choose what's in scope, and what we exclude.
Every call on this page is reasoned. We publish the full rubric for severity tiers, the medication inclusion logic, the evidence grades we accept, and what we deliberately leave out. About three thousand words. Worth reading once if you use this tool more than occasionally.
Read the full methodologyA full supplement review, built around you, not a generic stack.
The free checker answers one interaction question at a time. A Distil report reviews the bigger picture: your goals, diet, medications, current supplements and any blood results you provide, then shows what appears worth keeping, changing, adding or leaving out.
- what your diet already covers, so you are not adding a capsule for something food is already handling
- which evidence-graded compounds are worth considering for your goals, and which were considered but left out
- what to keep, change or stop from what you already take, plus the order to introduce anything new
- how your medications and complete supplement stack fit together, with daily timing and a clear point for reassessment
The interaction check is one section of the full report. You also get the reasoning behind each recommendation and the evidence references used.
£49 introductory price for early customers. Standard price £79.
Something missing?
If a supplement or medication you take isn't in our autocomplete, tell us. We go through what people flag every week and add what's missing.