Yes, the main ingredient in carbonate of magnesia climbing chalk is magnesium carbonate, which is also the active ingredient in many antacids.

Here's why:

* Magnesium carbonate is a basic compound that neutralizes stomach acid. This is why it's used in antacids to relieve heartburn and indigestion.

* Climbing chalk uses magnesium carbonate to absorb moisture from the hands, improving grip on the climbing surface.

While they share the same active ingredient, the formulation and intended use differ:

* Antacids are formulated for oral consumption and are designed to neutralize stomach acid quickly.

* Climbing chalk is formulated for external use and is designed to absorb moisture and improve grip.

So, while both products contain magnesium carbonate, they are not interchangeable. You should not use climbing chalk as an antacid and vice versa.