The reason why it hurts more when you take metronidazole for a toothache is that metronidazole can only inhibit the development of inflammation, not eliminate it. Inflammation can not be completely treated, the pain can not be completely eliminated. 1. Toothache is usually caused by pulpitis or periapical inflammation, most of the pulpitis and periapical inflammation occurs with anaerobic bacteria infection, metronidazole has a certain effect on the control of anaerobic bacteria infection, but can not completely eliminate the inflammation. 2. Inflammation that remains in the pulp or periapical tissues will continue to cause pain and damage to the surrounding tissues, which will lead to more and more severe pain, and the use of medications for infections in the pulp is almost ineffective. Metronidazole should be used under the guidance of a doctor. If the pain is severe, it is recommended to visit a hospital in time for treatment according to the specific cause.