The causes of bitter mouth after taking cold medicine are related to cold medicine ingredients, cold medicine’s stimulation to gastrointestinal tract, and decreased immunity. 1. Cold medicine ingredients: some cold medicines have the nature of traditional Chinese medicine, and the Chinese medicine ingredients in them can cause spleen and stomach disharmony and produce a bitter mouth reaction. Some cold medicines themselves have a bitter taste, and flavoring agents can be used to assist in the improvement of clinical symptoms when using the medicines. 2. Gastrointestinal stimulation: cold medicines may also stimulate the gastrointestinal tract, causing gastrointestinal dysfunction, indigestion, and bile reflux, thus making the patient’s mouth bitter. Generally it can be relieved after stopping taking cold medicine. 3. Decreased immunity: Colds can also reduce the body’s immunity, making the tongue thick and greasy, the mucous membrane in the mouth becomes dry, the gastrointestinal tract peristalsis slows down, resulting in decreased digestion and absorption ability, loss of appetite, bitter mouth. Bitter mouth after taking cold medicine may also be other causes, such as cholecystitis, gastroesophageal reflux disease, etc., please consult the hospital in time for active diagnosis and treatment. Patients should drink plenty of warm boiled water, maintain oral hygiene, do not eat spicy and irritating food.