Calcium Carbonate (Tums)

What is Calcium Carbonate (Tums)?

What calcium carbonate is

Calcium carbonate is the active ingredient in Tums and many other antacids (it is also the calcium in supplements like Caltrate and a common food additive, E170). As an antacid it works locally in the stomach, neutralizing excess gastric acid to relieve heartburn and acid reflux within minutes. Very little is absorbed into the bloodstream — most acts in the gut, and the calcium it releases is the same mineral your body needs every day.

Why it is considered safe in pregnancy

Calcium-carbonate antacids are widely recommended as a first-line treatment for the heartburn that affects most pregnancies, especially in the second and third trimesters as the growing uterus presses on the stomach. Because the carbonate acts locally and calcium is an essential nutrient during pregnancy, occasional-to-regular use at label doses is regarded as safe across all trimesters.

How to use it safely

Follow the package directions and do not exceed the maximum daily dose on the label. A few points specific to pregnancy:

• Mind your total calcium. Tums counts toward your daily calcium. With prenatal vitamins and diet, aim to stay under roughly 2,500 mg of total calcium per day.
• Separate it from iron. Calcium blocks iron absorption, so take calcium-carbonate antacids a couple of hours apart from any iron supplement — important since many pregnant people take iron.
• Watch for constipation. Calcium can be constipating; stay hydrated and keep up fiber.
• Choose a simple formula. Plain calcium-carbonate Tums is the straightforward choice. Avoid antacids that add aspirin (e.g., some Alka-Seltzer products) or that are very high in sodium.

When to talk to your doctor

Antacids are for occasional relief. Reach out to your provider if you need them most days, if heartburn is severe or wakes you at night, or if you have trouble swallowing, vomiting, or weight loss. Extremely high, prolonged calcium-carbonate use can rarely cause milk-alkali syndrome (high blood calcium) — another reason to stick to label doses.

For dosing, timing, and natural heartburn-relief tips, see our full guide: Is Tums Safe During Pregnancy? Dosage & Heartburn Relief. You can also scan any antacid or supplement with the SafeMom app for an instant pregnancy verdict.