bacterial infection
"I didn't notice the heartburn until the second day of taking the medicine and it wasn't really too bad until the fourth.. that's when I decided to read the label.  Here's the thing with this one, I think the main problem is the capsule and our tendency to take medicine just before going to bed - with this one that is very bad!  I can take pretty much any pill without water (I wasn't doing that), I almost *never* get heartburn and it took me a while to figure out what was going on. Reading the pill container label it specifically tells you - do not lie down for at least 10 minutes after taking this.  That should be your first warning that this one doesn't go down easily.  So drink plenty of water with it and be prepared for the burn."