Metronidazole
"I was prescribed 500mg 2 tablets daily for 3 days. The first day it gave me the worst headache ever and I actually walked out on my GED test because I got so dizzy and sick that I had to vomit and I went home and vomited about 3 more times. That was later in the evening. The second day I had a slight headache and later towards the evening (about the same time) I started getting sick to my stomach again. I have yet to go the last day, but I guess I can handle just 1 more day as long as it gets rid of the problem it was prescribed for. This pill works but the side effects are horrible for me. "