Background: We assessed the efficacy and safety of the oral glucagon-like peptide-1 analogue, semaglutide 50 mg, taken once per day versus placebo for the treatment of overweight or obesity in adults without type 2 diabetes. Methods: This randomised, double-blind, placebo-controlled, phase 3, superiority trial enrolled adults with a BMI of at least 30 kg/m², or at least 27 kg/m² with bodyweight-related complications and comorbidities, without type 2 diabetes. The trial was done at 50 outpatient clinics in nine countries across Asia, Europe, and North America. Participants were randomly allocated (1:1) via an interactive web-response system to oral semaglutide escalated to 50 mg, or visually matching placebo, once per day for 68 weeks, plus lifestyle intervention. Group assignment was masked for participants, investigators, and those assessing outcomes. Coprimary endpoints were the percentage change in bodyweight and whether participants reached a bodyweight reduction of at least 5% at week 68 for oral semaglutide 50 mg versus placebo, assessed regardless of treatment discontinuation or use of other bodyweight-lowering therapies (an intention-to-treat analysis). Safety was assessed in participants who received at least one dose of trial drug. This trial, registered with ClinicalTrials.gov (NCT05035095), is now complete. Findings: From Sept 13 to Nov 22, 2021, 709 participants were screened, of whom 667 were randomly assigned to oral semaglutide 50 mg (n=334) or placebo (n=333). The estimated mean bodyweight change from baseline to week 68 was –15·1% (SE 0·5) with oral semaglutide 50 mg versus –2·4% (0·5) with placebo (estimated treatment difference −12·7 percentage points, 95% CI −14·2 to −11·3; p<0·0001). More participants reached bodyweight reductions of at least 5% (269 [85%] of 317 vs 76 [26%] of 295; odds ratio [OR] 12·6, 95% CI 8·5 to 18·7; p<0·0001), 10% (220 [69%] vs 35 [12%]; OR 14·7, 9·6 to 22·6), 15% (170 [54%] vs 17 [6%]; OR 17·9, 10·4 to 30·7), and 20% (107 [34%] vs 8 [3%]; OR 18·5, 8·8 to 38·9) at week 68 with oral semaglutide 50 mg versus placebo. Adverse events were more frequent with oral semaglutide 50 mg (307 [92%] of 334) than with placebo (285 [86%] of 333). Gastrointestinal adverse events (mostly mild to moderate) were reported in 268 (80%) participants with oral semaglutide 50 mg and 154 (46%) with placebo. Interpretation: In adults with overweight or obesity without type 2 diabetes, oral semaglutide 50 mg once per day led to a superior and clinically meaningful decrease in bodyweight compared with placebo. Funding: Novo Nordisk.