The goal of this randomized, double-blind, placebo-controlled clinical trial is to assess whether the combination of N-acetylcysteine and simethicone improves mucosal visibility during upper gastrointestinal endoscopy in adults aged 18 to 99 years of both sexes, including both healthy individuals and those with non-bleeding gastrointestinal symptoms. The main questions this study aims to answer are: Does pre-endoscopy administration of N-acetylcysteine/simethicone improve mucosal visualization based on the Toronto Upper Gastrointestinal Cleanliness Score (TUGS)? Is this combination safe and well tolerated in this patient population? Researchers will compare patients receiving N-acetylcysteine (600 mg) and simethicone (100 mg) orally 20-60 minutes before the procedure with those receiving placebo (water) to determine if there is a significant improvement in TUGS scores. Participants will: Receive a single oral dose of either N-acetylcysteine/simethicone or placebo prior to endoscopy Undergo a routine upper GI endoscopy Have mucosal cleanliness evaluated using the TUGS scoring system Be monitored for any adverse events or intolerance