Conscious sedation is a popular technique for colonoscopy and upper gastrointestinal endoscopy. The combination of an opioid and a benzodiazepine is known to provide good analgesic and sedative conditions during endoscopy. This combination of opioid and benzodiazepine, however, also increases the risk of respiratory depression. Therefore, pharmacologic agents which may provide adequate sedation without respiratory depression are of great interest to clinicians.