Calcium carbonate: what it does and when to use it

Calcium carbonate shows up in two common places: as an antacid for heartburn (think chewable tablets) and as a cheap, effective calcium supplement for bone health. If you keep a tube of chewables in your cabinet or a bottle of supplement pills by your sink, you already know this stuff is everywhere. But when should you use it, and how do you avoid the common mistakes people make?

How to use calcium carbonate

If you’re taking it for heartburn or indigestion, chewable antacids work fast — chew the tablet and swallow. Follow the package directions or your doctor’s advice. For bone health, calcium carbonate provides a lot of elemental calcium per pill, so you may need fewer pills than with other forms. Most adults aim for about 1,000–1,200 mg of elemental calcium daily from all sources (food plus supplements), but check with your clinician for your exact target.

Important tip: calcium carbonate is best absorbed with food because it needs some stomach acid to dissolve. Take it with a meal rather than on an empty stomach. If your doctor prescribes it for low calcium, they’ll tell you how much elemental calcium you’re getting — that matters more than the pill weight.

Safety, interactions, and quick tips

Side effects are usually mild: constipation and gas are the most common. If you already have kidney disease or a history of kidney stones, talk to your doctor before taking it — high calcium can make those problems worse. Also avoid taking calcium carbonate at the same time as certain meds. Give space of 2–4 hours between calcium and antibiotics like tetracyclines or fluoroquinolones, thyroid pills (levothyroxine), bisphosphonates for bone loss, and iron supplements — calcium can block how well those drugs work.

How does it stack up against calcium citrate? Calcium carbonate contains more elemental calcium per pill and is cheaper, but calcium citrate absorbs well even if your stomach acid is low (useful for older adults or people on acid-reducing meds). If you’re on a proton pump inhibitor (PPI) or antacid regularly, your provider may suggest calcium citrate instead.

Pregnant or breastfeeding? Calcium is often safe and needed, but confirm the dose with your obstetrician. If you have a lot of stomach reflux and use antacids a lot, that’s also worth a chat with your clinician to avoid masking a more serious issue.

Quick checklist: take calcium carbonate with meals, check the label for elemental calcium, space it away from interacting meds, and watch for constipation. When in doubt, ask your pharmacist or doctor — they can recommend the right form and dose for your needs.

Want product options or more detailed guides on specific medications and interactions? Browse our articles and comparisons to find what fits your routine and health goals.