Sulfamethoxazole / trimethoprim
"I have been on Bactrim DS for 7 days. After day 3 I began to notice severe headache about 4 hours after taking the Bactrim. Now on day 7, I have not only had headache, but light-headedness/nausea. With only 3 days left, I am going to continue the medicine. My urinary tract infection symptoms have improved finally after 5 days."