If you have SIBO and GERD, it could be that you have low stomach acid. This could be caused by antacids like Zantac, Pepcid, Prevacid, Nexium, etc. Low stomach acid allows bacteria to flourish in the upper intestines and can also lead to GERD. Believe it or not, many people who complain of heartburn and take antacids would actually improve by taking hydrochloric acid (Betaine HCl).