Supplements and Risedronate sodium.
Risedronate sodium, sold under the brand names Actonel, Actonel Once a Week, is a bisphosphonate. Oral absorption is reduced by polyvalent cations including calcium, magnesium and iron.
Risedronate sodium 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 Risedronate sodium 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
Mineral chelation (absorption)
Calcium binds to risedronate in the gut and almost completely blocks how much you absorb. Take risedronate first thing on an empty stomach with plain water, stay upright for 30 minutes, then wait at least two hours before any calcium-containing food, drink or supplement.
Iron binds to risedronate in the gut and blocks absorption. Take risedronate first thing on an empty stomach with plain water, stay upright for 30 minutes, then wait at least two hours before any iron supplement.
Magnesium binds to risedronate in the gut and blocks absorption. Take risedronate first thing on an empty stomach with plain water, stay upright for 30 minutes, then wait at least two hours before any magnesium supplement.
Magnesium binds to risedronate in the gut and blocks absorption. Take risedronate first thing on an empty stomach with plain water, stay upright for 30 minutes, then wait at least two hours before any magnesium supplement.
Magnesium binds to risedronate in the gut and blocks absorption. Magnesium L-threonate is still elemental magnesium, so it has the same effect. Take risedronate first thing on an empty stomach with plain water, stay upright for 30 minutes, then wait at least two hours before any magnesium supplement.
Zinc is a divalent metal that can bind to risedronate in the gut and reduce how much you absorb, the same way calcium and iron do. Take risedronate on an empty stomach with plain water, stay upright for 30 minutes, then separate any zinc supplement by at least two hours.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Zinc is a divalent metal that can bind to risedronate in the gut and reduce how much you absorb, the same way calcium and iron do. Take risedronate on an empty stomach with plain water, stay upright for 30 minutes, then separate any zinc supplement by at least two hours.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Beneficial combination
These two are commonly and deliberately taken together. Risedronate works best when your vitamin D level is in a healthy range, and keeping vitamin D topped up lowers the small chance of your blood calcium dropping after a dose. This is a helpful pairing, not a clash. Take risedronate first thing on an empty stomach with plain water and stay upright for 30 minutes; you can take your vitamin D later in the day.
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.
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 methodologyWant this checked across everything you take?
This page checks the pairs you enter. The personalised Distil report goes further:
- the same graded, cited interaction check across your whole stack, not just the pairs you thought to type in
- where your current routine may be leaving you short of your goals
- the evidence-backed compounds worth adding, and the ones worth dropping
It's a paid report: £79, or £49 for the first 25 customers. The interactions check is one section of it, and you can read a real one in full before you buy.
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