A very bitter tongue after root canal treatment may be caused by improper treatment, sterilized water, or by the patient himself suffering from bile reflux and other diseases. 1. Improper treatment: The bitter tongue may be caused by the fact that the sealing of the tooth filled with root canal treatment has fallen off and there is an exposure of the medication. 2. Sterilized water: It may also be due to the need to sterilize the tooth as well as the mouth during root canal treatment, and the taste of sterilized water is rather bitter, thus this can occur. 3. Bile reflux: It may be caused by acute hepatitis, cholecystitis, duodenal ulcer and other diseases. When the pyloric function of the stomach is disturbed, the pyloric sphincter can be dysfunctional, and bile reflux can occur. When the bile refluxes into the mouth, the tongue can be very bitter. After ruling out root canal treatment-induced tongue bitterness, it is recommended that patients go to the hospital in time and follow the doctor’s instructions for treatment to avoid delaying the condition.