Background Total intravenous anesthesia (TIVA) is widely used as an anesthetic technique in patients undergoing colonoscopy. Lidocaine can reduce inflammation and visceral pain and potentiates the ventilatory responses to carbon dioxide. This study aimed to evaluate the efficacy and safety of lidocaine combined with propofol during a colonoscopy procedure. Methods The study had a prospective randomized controlled design and adhered to the CONSORT guidelines. Sixty-one patients underwent elective colonoscopy under TIVA with intravenous fentanyl 0.5 µg/kg and a loading dose of propofol 1 mg/kg followed by 2 mg/kg/h as a maintenance infusion with titration as needed. The patients were also randomized to receive 1.5 mg/kg of intravenous lidocaine followed by 2 mg/kg/h (L group) or 0.3 mL/kg of intravenous normal saline followed by 0.4 mL/kg/h (N group). The primary outcome was the total dose of propofol used during the colonoscopy. The secondary outcomes were complications and adverse events. Results Data for 60 patients were available for analysis. There was no statistically significant difference in the median total dose of propofol used between the L group and the N group (180 mg [interquartile range 150–270] vs 200 mg [interquartile range 150–250]) or in episodes of apnea (P ≥ 0.999) and desaturation (P = 0.547). The mean difference in mean arterial pressure at 5 minutes after scope insertion was significantly smaller in the N group than in the L group (P = 0.033). There was no statistically significant between-group difference in decrease in heart rate from baseline, number of episodes of hypotension or bradycardia, or any other adverse events. Conclusion Addition of intravenous lidocaine 1.5 mg/kg as a loading dose followed by lidocaine 2 mg/kg/h as a maintenance infusion did not decrease the dose of intravenous propofol used during a colonoscopy procedure. However, it was able to reduce the risk of hypotension in the early induction phase. Trial registration: The trial was registered retrospectively in the Thai Clinical Trial Registry (https://www.thaiclinicaltrials.org/show/TCTR20210902012) on 2 September 2021.