Inclusion Criteria:  Age ≥18 years old; Scheduled to undergo elective surgery under general anesthesia; Judged to be at high risk of postoperative nausea and vomiting. According to the Apfel's simplified score, patients with 3 or more of the following factors are at high-risk: women, non-smokers, history of PONV, postoperative use of opioids.  Exclusion Criteria:  Refuse to participate; Previous history of schizophrenia, epilepsy, Parkinson's disease or myasthenia gravis; Severe liver dysfunction (Child-Pugh class C); Severe renal dysfunction (dialysis required); Patients of the American Society of Anesthesiologists (ASA) grade 4 and above; Emergency surgery; Continuously taking benzodiazepines for more than 1 week before surgery; Any other circumstances that are considered unsuitable for study participation by attending physicians or investigators.