This is a randomized controlled trial to comparing the different simethicone administration strategies for esophagogastroscopy. Recent studies have indicated that the administration of simethicone before endoscopic examination could shorten the procedure time and improve the diagnostic rate of the gastric mucosal lesions. But the time interval between simethicone administration and the examination has not been fully determined. This study will test whether the time of taking simethicone before endoscopy could influence the performance of the procedure in a randomized controlled trial. The results may benefit the current clinical practice.

Esophagogastroscopy can enable the direct examination of the esophageal and gastric mucosal lesions, which has been widely applied in clinical practice. However, during the examination, too much water, foam or residues in the stomach will not only increase the procedure time and the misdiagnosis rate, but also decrease the patients' tolerance, for more efforts should be made to deal with the excessive water, foam or residues in order to obtain a clear view of the mucosa. Simethicone is also called poly-dimethylsiloxane, which can be used to remove the foam and water. Although simethicone has been routinely administrated before the esophagogastroscopy, the optimal strategy of administrating simethicone has not been clearly investigated, especially the time to administrate simethicone. Intaking simethicone too early will result in too excessive water in the stomach, while if the patients take it too late it doesn't take effects. Thus, this is a study to determine whether selecting different simethicone administration strategies could improve the performance of the esophagogastroscopy and minimize the patients' dissatisfaction.

Inclusion Criteria:

• Above 18 years old patients
• Who agree to participate in the study
• Patients with the indications for gastroduodenoscopy

Exclusion Criteria:

• Patients, who were receiving nonsteroidal anti-inflammatory drugs, pump inhibitors (PPI) or antibiotics in the last 3 weeks.
• Severe uncontrolled coagulopathy
• Prior history of gastric surgery.
• Pregnancy and lactation