Calcium supplements may interfere with alendronate absorption. However, one researcher suggested that addition of large amounts of supplemental calcium to alendronate therapy in patients with bone metastases (with evidence of osteomalacia) related to prostate cancer might improve the clinical outcome. Moreover, both calcium and alendronate are commonly used in the treatment of osteoporosis in the same people. To prevent potential interactions, alendronate should be taken two hours before or after calcium supplements.

Absorption of tiludronate, a drug related to alendronate, is reduced when taken with magnesium and/or aluminum-containing antacids. This interaction has not yet been reported with alendronate. Until more is known, alendronate should be taken two hours before or after magnesium and/or aluminum-containing antacids.