Metronidazole
"On the twice a day for 7 days, by the end of the second day I got a horrible headache while working out at the gym. I rarely get headaches so I attribute it to the med. I also have loss of appetite and periodic Nausea. The worst is this damn headache that I have had since last night and is still lingering tonight. Hopefully it will go away tomorrow but I cannot wait until I complete the dosage. I'm not gonna quit early bc I don't want to have to take this again."