Dacronin syrup, commonly known as dacronin hydrochloride syrup, is a local anesthetic used in the gastrointestinal tract, especially in upper gastrointestinal endoscopy, for laryngeal anesthesia and lubrication, as well as to remove foam from the lumen and make the field of vision clear, and must be applied under the guidance of a doctor’s prescription. This drug has some contraindications, for example, it is not suitable for allergic patients, for patients with acute diseases or serious damage to the mucosa of the digestive tract, the dose should be reduced as appropriate, this drug is not suitable for use with iodine contrast agent, because the combination with iodine will lead to iodine precipitates, interfering with the visual field.