calcium
26 interactions related to calcium
antibiotics + calcium
Calcium can bind to certain antibiotics (tetracyclines and fluoroquinolones) in the gut and reduce how much of the drug is absorbed.
calcium + zinc
A large calcium dose may modestly reduce zinc absorption in some conditions, but human evidence is mixed and the effect is not clinically dangerous.
vitamin d + vitamin k2
Vitamin D and vitamin K2 act synergistically on calcium metabolism: vitamin D increases calcium absorption while vitamin K2 activates osteocalcin and matrix Gla protein to direct calcium into bone and away from soft tissue. The main caution is for people taking warfarin.
vitamin d3 + vitamin k2
Vitamin D3 increases calcium absorption and stimulates production of vitamin K-dependent proteins (osteocalcin, matrix Gla protein) that require vitamin K2 to be activated. Taking the two together is a common, well-tolerated pairing that supports bone health. A separate, established interaction matters here: vitamin K2 reduces the effect of warfarin and other vitamin K antagonists.
atenolol + calcium
Calcium supplements and calcium-based antacids taken at the same time as atenolol bind it in the gut and reduce how much of the drug is absorbed, blunting its blood-pressure and heart-rate effects. Separating the two doses by several hours preserves atenolol's effect. Calcium from ordinary meals is generally not a concern.
hydrochlorothiazide + calcium
Thiazide diuretics such as hydrochlorothiazide increase the kidney's reabsorption of calcium and reduce how much calcium leaves the body in urine. This calcium-sparing effect is often beneficial, but combined with generous calcium supplements, high-dose vitamin D, or underlying parathyroid disease it can push blood calcium too high (hypercalcemia).
amlodipine + calcium
In theory, supplemental calcium could slightly blunt the blood-pressure-lowering effect of calcium channel blockers such as amlodipine, but controlled human data do not show a meaningful effect. Drugs.com flags this as a minor, monitor-only interaction with weak clinical evidence.
levothyroxine + calcium
Calcium can reduce levothyroxine absorption when the two are taken close together
doxycycline + calcium
Calcium binds doxycycline in the gut, forming a complex the body cannot fully absorb. Taking doxycycline together with calcium supplements, calcium-based antacids, or large dairy servings can lower how much antibiotic reaches the bloodstream, though doxycycline binds calcium less than older tetracyclines.
calcium + iron
Calcium can reduce the absorption of iron when the two are taken together, with the effect most pronounced for non-heme iron from supplements and plant foods.
omeprazole + calcium
Omeprazole strongly suppresses stomach acid, and calcium carbonate (the most common supplemental form) needs that acid to dissolve and be absorbed efficiently, especially on an empty stomach. Calcium citrate absorbs well regardless of stomach acid. Long-term proton pump inhibitor use is also associated with a modestly increased risk of hip, wrist, and spine fractures, which prompted an FDA labeling change.
risedronate + calcium
Calcium and other divalent cations bind risedronate in the gut and form insoluble complexes, blocking absorption of a drug whose oral bioavailability is already very low. Taking them together can reduce the absorbed amount to subtherapeutic levels and quietly undermine osteoporosis treatment.
tetracycline + calcium
Calcium binds to tetracycline in the gut, forming an insoluble chelate that the intestine cannot absorb. Dairy products, calcium supplements, and calcium-based antacids can sharply reduce how much tetracycline reaches your bloodstream, which can drop levels below what is needed to treat the infection.
prednisone + calcium
Glucocorticoids like prednisone impair intestinal calcium absorption and increase urinary calcium loss, contributing to a negative calcium balance and accelerated bone loss. This is a depletion-and-displacement effect, not a chemical interaction in the gut, and it is why calcium and vitamin D are treated as the foundation of bone protection during long-term steroid therapy.
calcium + magnesium
Calcium and magnesium work together in bone mineralization, muscle contraction, and nerve signaling. They share some intestinal absorption pathways, so very large single doses of one can modestly reduce uptake of the other. A balanced intake of both, weighted toward food, supports bone health better than emphasizing calcium alone.
boron + calcium
Boron is an ultratrace mineral that appears to reduce urinary calcium loss and to support the activity of vitamin D, which governs how much calcium the gut absorbs. In short-term feeding studies of postmenopausal women, adding boron lowered urinary calcium excretion and modestly raised estradiol. The effect is supportive rather than dramatic and is most relevant when boron intake from food is low.
liothyronine + calcium
Calcium salts (carbonate, citrate, acetate) can bind thyroid hormone in the gut and reduce absorption of liothyronine (T3), much as they do with levothyroxine. Taking them together can blunt the effect of the dose and lead to less reliable thyroid replacement.
yogurt + antibiotics
The calcium in yogurt can bind to certain antibiotics — specifically the tetracyclines and fluoroquinolones — in the gut and reduce how much of the drug is absorbed. This is the same chelation interaction seen with milk. Penicillins and macrolides are not meaningfully affected. The fix is timing: take these antibiotics with water and keep yogurt and other calcium-rich foods a couple of hours apart from the dose.
dairy + digoxin
Dairy is a dietary source of calcium, and calcium status modestly influences how digoxin acts on the heart. The dietary-dairy effect is minor on its own; the more relevant scenario is large stacked calcium loads (dairy plus supplements plus calcium-containing antacids) or intravenous calcium in a hospital setting. Milk proteins may also slightly reduce digoxin absorption from oral doses, but the effect is small and usually not clinically meaningful.
phenytoin + calcium
Calcium-containing supplements and antacids can bind phenytoin in the gut and lower how much of the drug is absorbed when the two are taken together, which can reduce phenytoin's blood level. Separately, long-term phenytoin use can reduce calcium absorption by speeding up the breakdown of vitamin D, which is relevant to bone health over time.
ketoconazole + calcium
Calcium carbonate antacids and large calcium supplements neutralize stomach acid and raise gastric pH. Oral ketoconazole needs an acidic stomach to dissolve and be absorbed, so taking the two together can lower ketoconazole blood levels and reduce its antifungal effect.
vitamin k2 + calcium
Vitamin K2 activates osteocalcin and matrix Gla protein, two proteins that bind calcium and help direct it into the bone matrix while keeping it out of arterial walls. Taking calcium alongside adequate vitamin K2 supports bone health; the two nutrients work together rather than competing.
alendronate + calcium
Calcium binds alendronate in the gut and forms an insoluble complex, sharply reducing absorption of an already very poorly absorbed bisphosphonate. Taken together, the calcium can leave the osteoporosis drug clinically ineffective.
levofloxacin + calcium
Calcium binds (chelates) levofloxacin in the gastrointestinal tract, modestly lowering the antibiotic's peak blood level. Total drug exposure over the dosing interval is largely preserved, so the effect is smaller than with iron, magnesium, or aluminum. Separating the doses by a couple of hours avoids the interaction.
dairy + fluoroquinolones
Calcium and other metal ions in dairy products bind oral fluoroquinolone antibiotics in the gut, forming poorly absorbed chelate complexes that lower the amount of antibiotic reaching the bloodstream.
whey protein + iron
Whey protein is usually consumed alongside calcium-rich milk minerals, and calcium competes with iron for absorption in the gut. When taken at the same time, a whey-plus-iron serving can modestly lower how much iron you absorb. The effect is largely driven by calcium, is generally modest, and is easily offset by taking a vitamin C source with your iron.