Metronidazole
"I had a Duodenal Switch (a major weight loss surgery combining the vertical sleeve with rearranging one's intestines to minimize fat absorption) 9 yrs ago.  Since then I've had probs with gas and a stomach ulcer, both caused by H Pylori.  I've taken Flagyl twice.  I am now on Day 5 of this round, & I don't experience most of the side effects I see described.  (250 mg 3X per day) While the pill doesn't "taste" great, there are other meds that also don't, and I find this no more severe than those.  I don't  have a lingering bad taste.  I've had no diarrhea and have had more regular bowel movements.  I've had almost no gas.  My pain is gone.  I don't feel sick.  I am grateful for this drug!"