BackgroundPremedication in upper gastrointestinal endoscopy for higher lesions detection rate has not been well studied so far. This study aimed to confirm whether premedication could improve the detection rate of early cancer or precancerous lesions and mucosal visibility.MethodFrom July 2015 to December 2015, 7200 participants from 6 centers were screened by endoscopy with one of the 4 following premedications randomly: (1) water (group D); (2) pronase (group A); (3) simethicone (group B); (4) pronase and simethicone (group C). Early cancer and precancerous lesions detection rates were taken as the primary endpoints, and mucosal visibility was taken as the secondary endpoint. They were compared among four groups to determine different premedication effects in terms of different anatomical sites. Trial was registered at Chinese Clinical Trial Registry; the registration number is ChiCTR-IOR-17010985.ResultsThe upper gastrointestinal overall precancerous lesion detection rates among four groups were 8.7, 8.4, 10.0, and 10.3%, the overall early cancer detection rates were 1.3, 1.4%, 1.5, and 1.6%, both without significant difference (p = 0.138 and 0.878). However, the visibility score distributions between control group (D) and premedication groups (A, B, and C) were all statistically significant, with all anatomical sites p values < 0.001. Subgroup analyses, from 2 centers without screening before, also showed significant difference in esophageal (3.9, 3.3, 4.5, and 8.4% with p = 0.004) and overall (7.0, 5.5, 7.3, and 12.0% with p = 0.004) precancerous lesion detection rate.ConclusionsPremedication with pronase and simethicone may not increase lesion detection rates but could significantly increase the upper gastrointestinal mucosal visibility.