Calcium is a mineral that is an essential part of bones and teeth. The heart, nerves, and blood-clotting systems also need calcium to work.

Calcium is taken by mouth for treatment and prevention of low calcium levels and resulting bone conditions including muscle cramps (latent tetany), osteoporosis (weak bones due to low bone density), rickets (a condition in children involving softening of the bones), and osteomalacia (a softening of bones involving pain). Calcium is also taken by mouth to prevent falls and to prevent high levels of the parathyroid hormone (hyperparathyroidism). It is also taken by mouth for premenstrual syndrome (PMS), leg cramps and depression in pregnancy, high blood pressure in pregnancy (pre-eclampsia), and to improve bone development in the baby. Calcium is used to reduce the risk of cancer, stroke, and cardiovascular disease, to increase survival following a heart attack, to help retain teeth in the elderly, and to help with weight loss.

Some people take calcium by mouth to prevent diarrhea and seizures due to sudden decreases in calcium levels. It is also taken by mouth to prevent for complications after intestinal bypass surgery, high blood pressure, high cholesterol, diabetes, metabolic syndrome, Lyme disease, to reduce high fluoride levels in children, and to reduce high lead levels. Calcium is used to prevent vitamin B12 deficiency associated with the medication metformin. It is also used to increase survival in people who have had a heart attack.

Calcium carbonate is taken by mouth as an antacid for "heartburn." Calcium carbonate and calcium acetate are also taken by mouth to reduce phosphate levels in people with kidney disease.

Calcium is used as a mouth rinse to prevent and reduce pain and swelling inside of the mouth following chemotherapy. Calcium is given intravenously (by IV) for very low calcium levels of the blood and related symptoms. It is also used for high potassium levels in the blood, muscle cramps following spider bites, and during CPR (cardiopulmonary resuscitation). Calcium gluconate and gluceptate may be injected as a shot if calcium cannot be given by IV. Calcium-rich foods include milk and dairy products, kale and broccoli, as well as the calcium-enriched citrus juices, mineral water, canned fish with bones, and soy products processed with calcium.

Calcium can interact with many prescription medications, but sometimes the effects can be minimized by taking calcium at a different time. See the section titled "Are there any interactions with medications?"

How it works

The bones and teeth contain over 99% of the calcium in the human body. Calcium is also found in the blood, muscles, and other tissue. Calcium in the bones can be used as a reserve that can be released into the body as needed. The concentration of calcium in the body tends to decline as we age because it is released from the body through sweat, skin cells, and waste. In addition, as women age, absorption of calcium tends to decline due to reduced estrogen levels. Calcium absorption can vary depending on race, gender, and age.

Bones are always breaking down and rebuilding, and calcium is needed for this process. Taking extra calcium helps the bones rebuild properly and stay strong.



Taking calcium carbonate by mouth as an antacid is effective for treating indigestion.

High levels of potassium in the blood (hyperkalemia)

Giving calcium gluconate intravenously (by IV) can reverse heart problems caused by hyperkalemia, a condition in which there is too much potassium in the blood.

Low levels of calcium in the blood (hypocalcemia)

Taking calcium by mouth is effective for treating and preventing hypocalcemia. Also, giving calcium intravenously (by IV) is effective for treating very low levels of calcium.

Kidney failure

Taking calcium carbonate or calcium acetate by mouth is effective for controlling high phosphate levels in the blood in people with kidney failure. Calcium citrate is not effective for treating this condition.


Likely safe

Calcium is LIKELY SAFE for most people when taken by mouth or when given intravenously (by IV) and appropriately. Calcium can cause some minor side effects such as belching or gas

Possibly unsafe

Calcium is POSSIBLY UNSAFE for both adults and children when taken by mouth in high doses. Avoid taking too much calcium. The Institute of Medicine sets the daily tolerable upper intake level (UL) for calcium based on age as follows: Age 0-6 months, 1000 mg; 6-12 months, 1500 mg; 1-8 years, 2500 mg; 9-18 years, 3000 mg; 19-50 years, 2500 mg; 51+ years, 2000 mg. Higher doses increase the chance of having serious side effects, such as blood levels of calcium that are too high and milk-alkali syndrome, a condition that can lead to renal stones, kidney failure and death. There is also concern that supplemental calcium can increase the risk of heart attack. Some research shows that taking calcium, often in amounts over the recommended daily intake level of 1000-1300 mg per day, is linked with an increased risk of heart attack in older people. But other research suggests there is no connection between calcium supplementation and heart attack risk. It may be that some groups have an increased risk while others do not. Continue consuming adequate amounts of calcium to meet daily requirements, but avoid excessive amounts of calcium. Be sure to consider total calcium intake from both dietary and supplemental sources and try not to exceed 1000-1200 mg of calcium per day. To figure out dietary calcium, count 300 mg/day from non-dairy foods plus 300 mg/cup of milk or fortified orange juice. Also, if calcium supplements need to be taken along with dietary calcium, consider taking ones that provide calcium along with vitamin D.



Pregnancy and breast-feeding: Calcium isLIKELY SAFEwhen taken by mouth in recommended amounts during pregnancy and breast-feeding. There is not enough information available on the safety of using calcium intravenously (by IV) during pregnancy andbreastfeeding.

Low acid levels in the stomach (achlorhydria). People with low levels of gastric acid absorb less calcium if calcium is taken on an empty stomach. However, low acid levels in the stomach do not appear to reduce calcium absorption if calcium is taken with food. Advise people with achlorhydria to take calcium supplements with meals.

High levels of phosphate in the blood (hyperphosphatemia) or low levels of phosphate in the blood (hypophosphatemia): Calcium and phosphate have to be in balance in the body. Taking too much calcium can throw this balance off and cause harm. Don't take extra calcium without your health provider's supervision.

Under-active thyroid (hypothyroidism): Calcium can interfere with thyroid hormone replacement treatment. Separate calcium and thyroid medications by at least 4 hours.

Too much calcium in the blood (as in parathyroid gland disorders and sarcoidosis): Calcium should be avoided if you have one of these conditions.

Poor kidney function: Calcium supplementation can increase the risk of having too much calcium in the blood in people with poor kidney function.

Smoking: People who smoke absorb less calcium from the stomach.

Stroke: Early research suggests that older women who have had a stroke, taking calcium supplements for 5 or more years might increase the chance of developing dementia. More research is needed to determine if calcium supplements should be avoided for those who have had a stroke.


Always consult with your doctor.
Ceftriaxone (Rocephin)

Administering intravenous ceftriaxone (Rocephin) and calcium can result in life-threatening damage to the lungs and kidneys. Calcium should not be administered intravenously within 48 hours of intravenous ceftriaxone (Rocephin).

Dolutegravir (Tivicay)

Dolutegravir (Tivicay) is a drug used to treat HIV. Taking calcium along with dolutegravir (Tivicay) can reduce blood levels of dolutegravir (Tivicay). Theoretically, this might decrease the effects of dolutegravir (Tivicay). To avoid this interaction, dolutegravir (Tivicay) should be taken 2 hours before or 6 hours after taking calcium.

Elvitegravir (Vitekta)

Elvitegravir (Vitekta) is a drug used to treat HIV. Taking calcium along with elvitegravir (Vitekta) can reduce blood levels of elvitegravir (Vitekta). Theoretically, this might decrease the effects of elvitegravir (Vitekta). To avoid this interaction, elvitegravir (Vitekta) should be taken 2 hours before or 2 hours after taking calcium.

Aluminum salts

Calcium citrate can increase how much aluminum your body absorbs when taken with aluminum hydroxide. This increase in aluminum levels might become toxic in people with kidney disease. However, not all forms of calcium cause this effect. Calcium acetate does not appear to increase aluminum absorption.

Calcipotriene (Dovonex)

Calcium might decrease how much antibiotic your body absorbs. Taking calcium along with some antibiotics known as "quinolones" might decrease their effectiveness. To avoid this interaction, take these drugs at least 2 hours before, or 4 to 6 hours after calcium supplements.Some quinolone antibiotics that might interact with calcium include ciprofloxacin (Cipro), levofloxacin (Levaquin), ofloxacin (Floxin), moxifloxacin (Avelox), gatifloxacin (Tequin), gemifloxacin (Factive), and others.In the stomach, calcium can bind to some antibiotics called tetracyclines. This decreases the amount of tetracyclines that can be absorbed. Taking calcium with tetracyclines might decrease the effectiveness of tetracyclines. To avoid this interaction, take calcium at least 2 hours before or 4 to 6 hours after taking tetracyclines.Some tetracyclines include demeclocycline (Declomycin), minocycline (Minocin), and tetracycline (Achromycin, and others).Calcium can decrease how much bisphosphate your body absorbs. Taking calcium along with bisphosphates can decrease the effectiveness of bisphosphate. To avoid this interaction, take bisphosphonate at least 30 minutes before calcium or, preferably, at a different time of day.Some bisphosphonates include alendronate (Fosamax), etidronate (Didronel), ibandronate (Boniva), risedronate (Actonel), tiludronate (Skelid), and others.Calcipotriene (Dovonex) is a drug that is similar to vitamin D. Vitamin D helps your body absorb calcium. Taking calcium supplements along with calcipotriene (Dovonex) might cause the body to have too much calcium.

Digoxin (Lanoxin)

Calcium can affect your heart. Digoxin (Lanoxin) is used to help your heart beat stronger. Taking calcium along with digoxin (Lanoxin) might increase the effects of digoxin (Lanoxin) and lead to an irregular heartbeat. If you are taking digoxin (Lanoxin), talk to your doctor before taking calcium supplements.

Diltiazem (Cardizem, Dilacor, Tiazac)

Calcium can affect your heart. Diltiazem (Cardizem, Dilacor, Tiazac) can also affect your heart. Taking large amounts of calcium along with diltiazem (Cardizem, Dilacor, Tiazac) might decrease the effectiveness of diltiazem (Cardizem, Dilacor, Tiazac).


Levothyroxine is used for low thyroid function. Calcium can decrease how much levothyroxine your body absorbs. Taking calcium along with levothyroxine might decrease the effectiveness of levothyroxine. Levothyroxine and calcium should be taken at least 4 hours apart.Some brands that contain levothyroxine include Armour Thyroid, Eltroxin, Estre, Euthyrox, Levo-T, Levothroid, Levoxyl, Synthroid, Unithroid, and others.Long-term lithium use can increase calcium levels in the blood. Taking lithium with calcium supplements might increase this risk of calcium levels becoming too high.

Raltegravir (Isentress)

Raltegravir (Isentress) is a drug used to treat HIV. Taking calcium along with raltegravir (Isentress) for several months might reduce blood levels of raltegravir (Isentress) and decrease its effects. Taking a single dose of calcium along with raltegravir (Isentress) does not appear to affect blood levels of raltegravir (Isentress).

Sotalol (Betapace)

Taking calcium with sotalol (Betapace) can decrease how much sotalol (Betapace) your body absorbs. Taking calcium along with sotalol (Betapace) might decrease the effectiveness of sotalol (Betapace). To avoid this interaction, take calcium at least 2 hours before or 4 hours after taking sotalol (Betapace).

Verapamil (Calan, Covera, Isoptin, Verelan)

Calcium can affect your heart. Verapamil (Calan, Covera, Isoptin, Verelan) can also affect your heart. Do not take large amounts of calcium if you are taking verapamil (Calan, Covera, Isoptin, Verelan).


Some "water pills" increase the amount of calcium in your body. Taking large amounts of calcium with some "water pills" might cause there to be too much calcium in the body. This could cause serious side effects, including kidney problems.Some of these "water pills" include chlorothiazide (Diuril), hydrochlorothiazide (HydroDIURIL, Esidrix), indapamide (Lozol), metolazone (Zaroxolyn), and chlorthalidone (Hygroton).Estrogen helps your body absorb calcium. Taking estrogen pills along with large amounts of calcium might increase calcium in the body too much.

The information provided on this page is for reference purposes and is not meant to be used as a medical advice, diagnosis or treatment. Always consult with a medical professional.