In a study of 20 people with GERD, chewable calcium carbonate was compared to swallowable tablets, bi-carb soda solutions or placebo for any effect on acid levels. Volunteers were first given foods that are known triggers for heartburn: cheese, chilli, raw onions and soft drink. Acid levels were monitored for the next 5.5 hours. Within half an hour, the chewable tablets reduced acid much more effectively than swallowed tablets. While oesophageal pH rose significantly, there was no decrease in stomach acid (a higher pH means less acid). A second study tested the effects of calcium carbonate on oesophageal motility, i.e. its ability to contract and push its contents into the stomach, where they belong. For this one, 18 heartburn sufferers were given a tablespoon of acid to swallow. Researchers then measured the amount of time and number of swallows that it took to raise the oesophageal pH back to 5 (mildly acidic). Without calcium carbonate, it took 20 swallows and 12 minutes. With the mineral, it took 12 swallows and 6 minutes.
As for licorice, a randomised, placebo-controlled trial aimed to test the effects of deglycyrrhyzinated licorice extract (DGL) on functional dyspepsia, a condition that includes heartburn as one of its symptoms. Patients given the licorice extract experienced a 51% reduction in their symptom scores, compared to 29% in the placebo group. 56% of those given the extract saw improvements in global efficacy scores, compared to no one in the placebo group. Overall, you don't have to live with either heartburn or the side effects of PPIs, although it is best to see a degree-qualified naturopath.