Calcium carbonate: what it is and how to use it safely

Calcium carbonate is a common antacid and a widely used calcium supplement. You’ll find it in chewable tablets (like Tums), pill supplements, powders, and food products. The key fact to remember: calcium carbonate is about 40% elemental calcium. That matters when you read labels—1,000 mg of calcium carbonate gives roughly 400 mg of actual calcium.

When to use it and dosing basics

Use calcium carbonate for short-term heartburn relief or to boost daily calcium intake. As an antacid, chewable doses work fast—take them when symptoms start. As a supplement, most adults aim for 1,000–1,200 mg of elemental calcium per day from all sources. If you rely on calcium carbonate, check how much elemental calcium each tablet provides and add dietary calcium when needed.

Timing matters. Calcium carbonate needs stomach acid to absorb well, so take it with meals. If you take it as an antacid, chew the tablet for quicker action. For daily supplements, split doses (for example, morning and evening) rather than taking a large single dose—your body absorbs smaller amounts better.

Interactions and safety tips

Calcium carbonate interferes with some drugs. Common issues include weaker effects of levothyroxine, reduced absorption of iron and some antibiotics (tetracyclines, fluoroquinolones), and problems with bisphosphonates (like alendronate). To avoid trouble, separate calcium carbonate from these meds: give thyroid pills 4 hours before or after calcium, and keep a 2–4 hour gap for many antibiotics and iron supplements. Always follow your doctor’s timing advice.

Side effects are usually mild: constipation, gas, and belching are the most common. Watch for signs of high calcium (nausea, vomiting, excessive thirst, confusion, frequent urination) — those need medical attention. If you have kidney disease or a history of kidney stones, check with your provider before taking calcium carbonate. People on certain heart or blood pressure meds should get specific advice from their prescriber.

Pregnant and breastfeeding women often use calcium supplements but should confirm the dose with their clinician. Don’t guess at the right amount—too little leaves you short; too much raises risks.

Practical tips: read labels for elemental calcium, choose calcium citrate if you have low stomach acid or take acid-reducing drugs, chew antacids for fast relief, and space calcium away from interacting medicines. When in doubt, ask your pharmacist or doctor—small changes in timing or form make a big difference in safety and benefit.