The course of metronidazole for toothache is usually 5 to 10 days, do not take more than 10 days. Long-term use may lead to gastrointestinal reactions, neurological reactions, leukopenia and other reactions, as follows. 1. Digestive tract reaction: long-term use of metronidazole may lead to nausea, vomiting, anorexia, abdominal pain and other symptoms. 2. Neurological reactions: long-term use of metronidazole may cause dizziness, ataxia, polyneuritis and other symptoms. 3. Leukopenia: temporary and reversible leukopenia may occur in a few patients after long-term use. It should be noted that there are a variety of causes of toothache, and some of the diseases that cause toothache are not obvious when taking metronidazole, and need to be treated accordingly. The drug should be used under the guidance of a doctor, and if the symptoms of toothache occur, it is recommended to go to the hospital in time, according to the cause of the treatment.