I had giardia in Maine and took flagyl. I felt fine in 24 hours and resumed my hike. I don't remember how many days of pills I took...seems like three and I had a few left over. Dysentery I had in the Middle East, Iran, and Nepal. For that I took Lomotil and it works great too. They are different, gairdia seems to have more gas and dysentery seems more tiring and debilitating. Good Luck.