Metronidazole
"I had this drug for a toothache and I had an A level exam (in England) the day after I was presribed the drug. I felt sick the whole day and during my exam with stabbing pains in my stomach and had to leave my exam at one point because I felt like I was you to throw up. I managed to finish the exam but when I got home I threw up several times and continued throwing up the next couple days after I stopped taking the drug"