Adenoma detection rate (ADR) is defined as the proportion of screening colonoscopies performed by a physician that detect at least one histologically-confirmed colorectal adenoma or adenocarcinoma. Colonoscopy is considered the gold standard for polyp detection and removal. However, there is still a significant number of missed polyps during colonoscopy. L-Menthol (peppermint oil) has been shown to induce spasmolytic effects in human colon smooth muscle, therefore, it could potentially improve the visual field for the endoscopist. The aim of our study was to determine the effectiveness and safety of topical L-menthol in adenoma detection and to evaluate the effect on colonic peristalsis. This was a randomized, double-blind, controlled trial conducted at the University of Alberta Hospital. Patients undergoing screening colonoscopy were consecutively recruited from the Stop Colorectal Cancer through Prevention and Education program . Patients were randomized to L-Menthol solution or the control solution (liquid simethicone) administered as spray at the cecum during colonoscopy. The degree of peristalsis was recorded at baseline, then at 1 and 5 minutes and graded as none, mild, moderate or severe, based on a validated classification. The endoscopists and patients were blinded to the allocated solution. During the procedure, insertion and withdrawal time were recorded, quality of bowel preparation, total sedation, changes to patient position, abdominal pressure and the use of carbon dioxide. The location, size, removal technique and type of polyp detected were documented. All specimens retrieved were sent for histopathology. After the procedure, patients were contacted and questioned about bloating, abdominal pain, and other adverse effects. Out of a total of 122 patients enrolled in our study, 61 patients were randomized to receive L-Menthol. There were no significant differences in patient characteristics between the two groups. The overall ADR was 63.1%. There were no significant differences in amount of sedation, position change, or withdrawal time. The primary end point of ADR was 57.4% in the L-menthol group and 68.9% in placebo (p=0.260). The proportion of patients with no peristalsis at five minutes was 44.3% in the L-menthol group and 21.3% in the control group (p=0.002). There were no significant differences in peristalsis at baseline and after one minute between both groups. No significant differences were found regarding bloating or abdominal pain between the two groups. No major side effects were reported in the two groups. Topical L-menthol was associated with decreased peristalsis during colonoscopy after 5 minutes of spraying. L-Menthol did not increase the ADR in intermediate-risk patients, however, further studies on other patient populations should be considered to evaluate the effect on ADR.