We aimed to evaluate the potential anxiolytic effects of premedication with pregabalin, compared with diazepam and placebo. We conducted this non-inferiority, double-blind, randomized controlled trial in ASA classification I-II patients aged 18–70 years, scheduled for elective surgery under general anesthesia. They were allocated to receive pregabalin (75 mg the night before surgery and 150 mg 2 h before surgery), diazepam (5 and 10 mg in the same manner) or placebo. Preoperative anxiety was evaluated using verbal numerical rating scale (VNRS) and Amsterdam Preoperative Anxiety and Information Scale (APAIS) before and after premedication. Sleep quality, sedation level, and adverse effects were assessed as secondary outcomes. A total of 231 patients were screened and 224 completed the trial. The mean change (95%CI) in anxiety scores from before to after medication in pregabalin, diazepam, and placebo groups for VNRS were − 0.87 (− 1.43, − 0.30), − 1.17 (− 1.74, − 0.60), and − 0.99 (− 1.56, − 0.41), and for APAIS were − 0.38 (− 1.04, 0.28), − 0.83 (− 1.49, − 0.16), and − 0.27 (− 0.95, 0.40). The difference in change for pregabalin versus diazepam was 0.30 (− 0.50, 1.11) for VNRS and 0.45 (− 0.49, 1.38) for APAIS, exceeding the limit of inferiority for APAIS of 1.3. Sleep quality was statistically different between pregabalin and placebo groups (p= 0.048). Sedation in pregabalin and diazepam groups were significantly higher than placebo group (p= 0.008). No significant differences of other side effects, except dry mouth was higher in placebo group compared with diazepam (p= 0.006). The study filed to provide evidence at non-inferiority of pregabalin compared to diazepam. Furthermore, premedication with either pregabalin or diazepam did not significantly reduce the preoperative anxiety in comparison to placebo, despite the fact that both resulted in higher levels of sedation. Clinicians should weigh the benefits and risks of premedication with these 2 drugs.Thai Clinical Trials Registry: TCTR20190424001 (24/04/2019) Registry URL:https://www.thaiclinicaltrials.org/.