NutriStack
Calcium and Risedronate, timing-sensitive.
Risedronate forms insoluble chelates with calcium in the gut, which can drop its already low oral bioavailability (~1%) to near zero. Even calcium from mineral water taken at the same time has been shown to significantly reduce risedronate absorption. Without separation, the dose may be largely wasted and bone protection lost.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
Same shape as the other 1,729 pairs in the public database.
From the interaction database
What the row says.
Every entry follows the same shape: what is happening, the mechanism, the recommendation, and the primary literature.
At a glance
- Substances
- Calcium and Risedronate
- Pair type
- Timing Sensitive
- Evidence (highest tier)
- Strong
- Source citations
- 3 sources
- Stack Score effect
- −5 to your Stack Score (per scored timing-sensitive row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Timing Sensitive · Strong evidence
Timing Sensitive
What is happening. Risedronate forms insoluble chelates with calcium in the gut, which can drop its already low oral bioavailability (~1%) to near zero. Even calcium from mineral water taken at the same time has been shown to significantly reduce risedronate absorption. Without separation, the dose may be largely wasted and bone protection lost.
Mechanism. The bisphosphonate phosphonate groups bind avidly to divalent cations such as Ca2+, forming non-absorbable complexes in the lumen and blocking transcellular and paracellular uptake in the proximal small intestine.
Recommendation. Take risedronate first thing in the morning with plain tap water only, then wait at least 30 minutes (60 minutes is safer) before any calcium supplement, dairy, fortified juice, or mineral water. If you forget and take them together, that dose will likely not work.
Minimum separation. 60
Sources (3)
- Kim JS, Jang SW, Son M, Kim BM, Kang MJ. Enteric-coated tablet of risedronate sodium in combination with phytic acid, a natural chelating agent, for improved oral bioavailability. Eur J Pharm Sci. 2016;82:36-42. PMID 26594027
- Itoh A, Akagi Y, Shimomura H, Aoyama T. Interaction between Bisphosphonates and Mineral Water: Study of Oral Risedronate Absorption in Rats. Biol Pharm Bull. 2016;39(3):323-8. PMID 26934925
- Wiesner A, Szuta M, Galanty A, Paśko P. Optimal Dosing Regimen of Osteoporosis Drugs in Relation to Food Intake as the Key for the Enhancement of the Treatment Effectiveness-A Concise Literature Review. Foods. 2021;10(4):720. PMID 33805435
Stack Score
How this pair moves the number.
Effect on the composite score
If both Calcium and Risedronate are in the same stack, this pair applies −5 to your Stack Score (per scored timing-sensitive row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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