Calcium Carbonate vs. Calcium Citrate: 4 Differences Between These Common Calcium Supplements

Getting enough calcium is important for your day-to-day health. Most people know that calcium is good for strong bones. But it also plays a role in muscle movement and nerve communication. It even helps your blood vessels move blood throughout the body. 

Calcium is available in many foods, including dairy products, green vegetables, and fortified breads and cereals. But if you can’t get all the calcium you need from food, your healthcare professional may recommend a calcium supplement. They may also recommend a supplement if you’re at high risk for having brittle bones, follow a vegan diet, or have a lactose intolerance.

If you’re interested in taking a calcium supplement, there are a lot of options out there. Calcium carbonate (Tums) and calcium citrate (Citracal) are two common calcium supplements. But these two products have a few key differences.

Calcium citrate vs. calcium carbonate differences at a glance

When comparing calcium carbonate versus calcium citrate, one supplement isn’t better than the other. They're both good choices if you have low calcium or you’re trying to prevent it. The one that’s best for you depends on a few factors.

• Why they’re taken: Calcium carbonate and calcium citrate both treat low calcium levels (hypocalcemia). But calcium carbonate also relieves heartburn and treats high phosphorus levels (hyperphosphatemia).

• How you take them: Calcium carbonate contains more elemental calcium than calcium citrate. Elemental calcium is the calcium that’s actually absorbed by the body. So you may need to take more calcium citrate than calcium carbonate to get the desired amount of calcium.

• How well they’re absorbed: To absorb calcium carbonate, you need enough acid in your stomach. You should take it with food to help with this. But calcium citrate can be taken without food. If you take medications that reduce stomach acid, calcium citrate may be a better option than calcium carbonate. This includes proton pump inhibitors or histamine-2 antagonists.

• What side effects they cause: Calcium carbonate and calcium citrate can cause similar side effects. But calcium carbonate is more likely to cause gastrointestinal side effects. This includes constipation, nausea, and bloating.

Below, we’ll dive into detail about these differences and more.

Disclosure

Calcium Carbonate

Avg retail price

$6.92(Save 63.29%)

GoodRx discount

$2.54

See all discounts

How it works

Use GoodRx to find medications, pharmacies, and discounts.

GoodRx discounts can help you pay less for your prescription.

Bring your free coupon or savings card to the pharmacy.

1. Why they’re taken

Calcium carbonate and calcium citrate are over-the-counter (OTC) calcium supplements. They prevent and treat hypocalcemia (low calcium). Low calcium can occur due to certain health conditions including vitamin D deficiency, kidney disease, and hypoparathyroidism.

However, one of calcium carbonate's most common uses is as an antacid (Tums) to treat heartburn and upset stomach. It also treats a condition called hyperphosphatemia in people living with kidney disease. Calcium citrate isn’t used as an antacid and isn’t the best option to treat hyperphosphatemia.

Good to know: Not getting enough calcium can make you more likely to develop osteoporosis (weak bones). And severely low calcium levels can cause seizures and heart problems. So if your healthcare professional recommends a calcium supplement, follow their recommendations for how to take it.

2. How you take them

Most adults should try to get 1,000 mg to 1,200 mg of elemental calcium per day. This includes calcium from your diet and any supplements. However, that number can vary from person to person. Your healthcare professional can tell you how much calcium you should try to get every day. They’ll let you know whether you need a supplement to boost your calcium levels.

Elemental calcium is the actual amount of calcium that your body absorbs. Calcium carbonate has more elemental calcium than calcium citrate (40% in carbonate versus 21% in citrate). So you may have to take more calcium citrate tablets to get the desired amount of calcium. Thankfully, you don’t have to do any calculations. The supplement label should tell you how much elemental calcium is in a dose.

Elemental calcium dosages of 500 mg or less have the best absorption. If you take more than 500 mg at a time, you’ll absorb less calcium.

If you’re using calcium carbonate as an antacid, learn the typical dosages for heartburn.

3. How they’re absorbed

Calcium carbonate needs an acidic stomach environment to be absorbed well. But calcium citrate doesn’t. So calcium citrate may be a better choice for people taking acid reflux medications. This includes omeprazole (Prilosec) and famotidine (Pepcid AC, Zantac 360). Calcium citrate may also be recommended over calcium carbonate for people with health conditions causing low stomach acid, such as achlorhydria.

Calcium carbonate is better absorbed with food. But calcium citrate absorption isn’t as affected by food. So you can take it without food. However, all calcium supplements, even calcium citrate, are generally best absorbed when taken with food.

Good to know: Vitamin D plays an important role in maintaining healthy calcium levels. If you don’t get enough vitamin D from sunlight, food, or supplements, you can’t absorb calcium properly. For this reason, calcium supplements are often combined with vitamin D.

4. Side effects

Calcium citrate and calcium carbonate can both cause constipation, nausea, and a loss of appetite. However, calcium carbonate seems to have a higher risk, especially in older adults with low levels of stomach acid. Sometimes switching to a different calcium formulation, drinking more fluids, or taking it with food can help. Taking smaller doses (but taking it more frequently during the day) may also help.

Overall, serious risks from calcium supplements are rare. But they’re more likely with high doses. Risks include heart problems, hypercalcemia, and kidney problems like kidney stones.

Some calcium supplement side effects may warrant a call to your healthcare professional (HCP). And sometimes, you may need emergency care. So if you notice anything unusual, like heart palpitations, vomiting, or confusion, reach out to your HCP immediately. If any symptoms feel severe, call 911 or seek emergency care.

Learn more about calcium carbonate side effects.

Can you take calcium supplements with other medications?

Calcium supplements can interact with many medications. So it’s best to have your pharmacist check for any interactions with your current medications, OTC products, or supplements prior to starting it.

There are a few ways calcium supplements can interact with other medications:

• Calcium may decrease the absorption of other medications. This means that these medications won’t be as effective as you’d expect. Examples include bisphosphonates like alendronate (Fosamax), antibiotics like ciprofloxacin (Cipro), and thyroid medications like levothyroxine (Synthroid). Calcium can also decrease the absorption of iron supplements.

• Other medications may decrease the absorption of calcium. For example, acid reflux medications like pantoprazole (Protonix) and famotidine may decrease absorption of calcium carbonate, making it less effective.

• Other medications can increase calcium levels. When combined with calcium supplements, this increases your risk for hypercalcemia. These include lithium (Lithobid), hydrochlorothiazide (Microzide), and high doses of vitamin D.

Good to know: Many medications can affect calcium levels. Some medications may decrease calcium, while others may increase calcium. 

Can you take calcium carbonate and calcium citrate together?

It’s not a good idea to take calcium carbonate and calcium citrate together. Combining them can increase your risk of side effects like constipation and nausea. More seriously, it can increase your risk of heart problems and hypercalcemia.

Because taking too much calcium is risky, it’s important to know if any of your OTC supplements or products contain calcium, including multivitamins. Calcium is also present in many OTC heartburn medications, including:

• Tums (calcium carbonate)

• Alka-Seltzer Extra Strength Heartburn Relief Chews (calcium carbonate)

• Rolaids (calcium carbonate / magnesium hydroxide)

If you need something for heartburn and you’re already taking a calcium supplement for another reason, consider an antacid that doesn’t have calcium. Examples include:

• Mylanta Maximum Strength Liquid Antacid/Anti-Gas (Aluminum hydroxide / magnesium hydroxide / simethicone)

• Alka-Seltzer Original Antacid (anhydrous citric acid / aspirin / sodium bicarbonate)

• Gaviscon Extra Strength Antacid (aluminum hydroxide / magnesium carbonate)

Why trust our experts?

Written by:

Amy B. Gragnolati, PharmD, BCPS

Amy Gragnolati, PharmD, BCPS, is a pharmacy editor for GoodRx. Amy currently holds her pharmacist license in Georgia and California.

Reviewed by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

Our editorial standards

Meet our experts