 Our pilot results showed that meperidine reduce patient discomfort during EGD esophagogastroduodenoscopy. But many patients can tolerate EGD well without any sedative agents. So the investigators target the use of meperidine on patients expected to have poor tolerance in this study, which includ young females with high anxiety level and patients with prior poor tolerance. The investigators test the hypothesis that meperidine improves tolerance and alleviates discomfort for patients expected to have poor tolerance during diagnostic EGD. 