Some medications like proton pump inhibitors* reduce stomach acids. However these are usually prescribed because the individual’s stomach acid levels are too high and the medication reduces the acids to a more normal level. You might consider calcium citrate rather than calcium carbonate if you are on these drugs.
*Clinically used proton pump inhibitors:
Omeprazole (brand names: Losec, Prilosec, Zegerid, ocid, Lomac, Omepral, Omez)
Lansoprazole (brand names: Prevacid, Zoton, Inhibitol, Levant, Lupizole)
Dexlansoprazole (brand name: Kapidex)
Esomeprazole (brand names: Nexium, Esotrex)
Pantoprazole (brand names: Protonix, Somac, Pantoloc, Pantozol, Zurcal, Pan)
Rabeprazole (brand names: Rabecid, Aciphex, Pariet, Rabeloc. Dorafem)