<<Disclaimer: Verify this information before applying it to your situation.>> I'm not sure which over-the-counter antacids are guaranteed gluten free, but I did just discover a brand that is available mail order. The company is called Puritan Pride and they are located in New York. They make muli-vitamins and antacids/calcium supplements among other things. I just ordered several bottles of their all natural chewable antacids with calcium, product #2220. They were pretty reasonably priced, the shipping wasn't too bad (UPS), and best of all, right now they have a two for one sale on them, so I will be getting 10 bottles of 100 instead of 5! I hope this info helps someone. Steve Veach in Chicago, Illinois USA