Can You Take Calcium and Magnesium at the Same Time?

Short answer: Yes, most healthy adults can take calcium and magnesium at the same time without a significant problem. However, staying within the limits set by the NIH Office of Dietary Supplements (ODS) and speaking with a clinician before combining supplements with any medication is always the right first step.

Why People Take These Two Minerals Together

Calcium and magnesium are both essential minerals that the body cannot make on its own. Many combination supplements pair them because they share overlapping roles in bone structure and muscle function. Understanding what each mineral does, how much is appropriate, and where the real cautions lie will help you make a more informed choice.

What Calcium Does in the Body

According to the NIH ODS, calcium makes up much of the structure of bones and teeth and keeps tissue rigid, strong, and flexible. It also mediates blood vessel contraction and dilation, and it supports normal muscle function. The evidence that calcium is required for these physiological roles is rated Strong by the ODS.

Research shows that supplemental calcium, alone or combined with vitamin D, increases bone mineral density in older adults (evidence rated Moderate). Calcium plus vitamin D may also support fracture outcomes in older adults, though that evidence is rated Limited. Claims about calcium and cancer risk are rated Insufficient, meaning current research does not support a conclusion either way.

What Magnesium Does in the Body

The NIH ODS describes magnesium as a cofactor in more than 300 enzyme systems that regulate diverse biochemical reactions, including protein synthesis. It supports normal muscle and nerve function, and it contributes to blood glucose control and blood pressure regulation. This foundational role is supported by Strong evidence.

Research also suggests that higher magnesium intake may help reduce the risk of high blood pressure, support bone mineral density, and is associated with lower risk of type 2 diabetes and cardiovascular disease. All of these associations are rated Limited, meaning they are promising but not conclusive. Magnesium's role in migraine prevention carries Moderate evidence, though doses used in migraine research often exceed the standard upper limit and should only be used under medical supervision.

How Much Is Recommended

The following figures come from the NIH ODS and the National Academies Dietary Reference Intakes.

Calcium Daily Targets

• Adults ages 19 to 50: 1,000 mg per day
• Women over age 50: 1,200 mg per day
• Men over age 70: 1,200 mg per day
• Tolerable Upper Intake Level (all sources combined): 2,500 mg per day for ages 19 to 50, and 2,000 mg per day for ages 51 and older

Magnesium Daily Targets

• Men ages 19 to 30: 400 mg per day; men 31 and older: 420 mg per day
• Women ages 19 to 30: 310 mg per day; women 31 and older: 320 mg per day
• Tolerable Upper Intake Level from supplements and medications only: 350 mg per day for anyone age 9 and older (this limit does not apply to magnesium naturally present in food and beverages)

Do Calcium and Magnesium Compete With Each Other?

You may have read that calcium and magnesium compete for absorption. At very high doses, minerals that share the same intestinal transport pathways can interfere with one another. However, at the amounts found in standard combination supplements and within the limits above, the NIH ODS does not flag this as a clinically meaningful concern for most healthy people. If you are trying to correct a deficiency in one mineral specifically, a clinician can advise whether separating doses makes sense for your situation.

One practical note on calcium: absorption is best when taken in single doses of 500 mg or less, and taking supplements with food also improves absorption. Splitting a larger calcium dose across two meals is a reasonable strategy regardless of whether you are also taking magnesium.

Safety Considerations

Magnesium from food is safe for healthy people because the kidneys excrete any excess. The supplemental upper limit of 350 mg per day exists mainly to avoid diarrhea and gastrointestinal discomfort. For calcium, staying below the Tolerable Upper Intake Level matters more: higher supplemental intakes may increase the risk of kidney stones and possibly cardiovascular disease, according to the ODS (evidence rated Limited).

As a reminder, dietary supplements are not intended to diagnose, treat, cure, or prevent any disease, and these statements have not been evaluated by the FDA.

Drug Interactions to Know

This is where caution becomes most important. Always talk to a doctor or pharmacist before combining either mineral with any medication.

Calcium Interactions

• Dolutegravir (HIV integrase inhibitor): calcium supplements can substantially reduce blood levels of this drug through chelation. Take dolutegravir 2 hours before or 6 hours after calcium.
• Levothyroxine (thyroid hormone): calcium carbonate can interfere with absorption. Separate doses by at least 4 hours.
• Lithium (bipolar disorder): long-term use can cause elevated calcium levels, and combining with calcium supplements may increase that risk.
• Quinolone antibiotics such as ciprofloxacin, gemifloxacin, and moxifloxacin: calcium reduces antibiotic absorption. Take the antibiotic 2 hours before or 2 hours after calcium.

Magnesium Interactions

• Bisphosphonates such as alendronate: magnesium-rich supplements can decrease absorption. Separate dosing by at least 2 hours.
• Tetracycline and quinolone antibiotics: magnesium can form insoluble complexes that reduce antibiotic absorption. Take these antibiotics at least 2 hours before or 4 to 6 hours after a magnesium supplement.
• Loop and thiazide diuretics such as furosemide and hydrochlorothiazide: chronic use can increase urinary magnesium loss and may lead to depletion.
• Potassium-sparing diuretics such as amiloride and spironolactone: these reduce magnesium excretion, which could raise magnesium levels when combined with supplementation.

Who Should Be Especially Careful

• People taking any of the medications listed above
• Anyone with kidney disease, as impaired kidneys are less able to regulate mineral excretion
• Older adults who may already be taking multiple supplements or medications
• Anyone considering doses above the Tolerable Upper Intake Levels noted by the NIH ODS

Bottom Line

For most healthy adults, taking calcium and magnesium together is not harmful when both are kept within the limits established by the NIH ODS. The more meaningful questions involve the medications you take, your total intake from food and supplements combined, and whether you have any health conditions that affect mineral metabolism. Consult a clinician or pharmacist for personal dosing guidance before starting or changing any supplement routine.