Background: Natural amylin is a pancreatic hormone that induces satiety. Cagrilintide is a long-acting amylin analogue under investigation for weight management. We assessed the dose-response relationship of cagrilintide regarding the effects on bodyweight, safety, and tolerability., Methods: We conducted a multicentre, randomised, double-blind, placebo-controlled and active-controlled, dose-finding phase 2 trial at 57 sites including hospitals, specialist clinics, and primary care centres in ten countries (Canada, Denmark, Finland, Ireland, Japan, Poland, Serbia, South Africa, the UK, and the USA). Eligible participants were adults aged at least 18 years without diabetes, with a body-mass index of at least 30 kg/m 2 or at least 27 kg/m 2 with hypertension or dyslipidaemia. Participants were randomly assigned (6:1) to subcutaneous self-injections of once-weekly cagrilintide (0·3, 0·6, 1·2, 2·4, or 4·5 mg), once-daily liraglutide 3·0 mg, or volume-matched placebo (for six placebo groups). The trial had a 26-week treatment period, including a dose-escalation period of up to 6 weeks, and a 6-week follow-up period without treatment. Participants and investigators were masked to the assigned study treatment with respect to active versus pooled placebo treatment, but not to different active treatments. The primary endpoint was the percentage change in bodyweight from baseline to week 26, assessed in all randomly assigned participants according to the trial product estimand (assuming all participants were adherent to treatment) and to the treatment policy estimand (regardless of adherence to treatment). Safety was assessed in all participants who received at least one dose of randomised treatment. This trial is registered with ClinicalTrials.gov, NCT03856047, and is closed to new participants., Findings: Between March 1 and Aug 19, 2019, we randomly assigned 706 participants to cagrilintide 0·3-4·5 mg (100-102 per dose group), 99 to liraglutide 3·0 mg, and 101 to placebo. Permanent treatment discontinuation (n=73 [10%]) occurred similarly across treatment groups, mostly due to adverse events (n=30 [4%]). In total, 29 participants (4%) withdrew from the trial. According to the trial product estimand, mean percentage weight reductions from baseline were greater with all doses of cagrilintide (0·3-4·5 mg, 6·0%-10·8% [6·4-11·5 kg]) versus placebo (3·0% [3·3 kg]; estimated treatment difference range 3·0%-7·8%; p<0·001). Weight reductions were also greater with cagrilintide 4·5 mg versus liraglutide 3·0 mg (10·8% [11·5 kg] vs 9·0% [9·6 kg]; estimated treatment difference 1·8%, p=0·03). Similar weight loss reductions were observed with the treatment policy estimand. The most frequent adverse events were gastrointestinal disorders (eg, nausea, constipation, and diarrhoea) and administration-site reactions. More participants receiving cagrilintide 0·3-4·5 mg had gastrointestinal adverse events compared with placebo (41%-63% vs 32%), primarily nausea (20%-47% vs 18%)., Interpretation: Treatment with cagrilintide in people with overweight and obesity led to significant reductions in bodyweight and was well tolerated. The findings support the development of molecules with novel mechanisms of action for weight management., Funding: Novo Nordisk A/S., Competing Interests: Declaration of interests DCWL is a consultant for, and has received speaker honoraria from, Amgen, AstraZeneca, Bausch Health, Boehringer Ingelheim, Eli Lilly, HLS Therapeutics, and Novo Nordisk; and has received research funding from AstraZeneca and Novo Nordisk. AS, AMF, and LE are employees and shareholders at Novo Nordisk A/S. CWlR is an advisory board member and speaker for Boehringer Ingelheim, GI Dynamics, Herbalife, Johnson & Johnson (J&J), Keyron, Novo Nordisk, and Sanofi; and has shares in Keyron. BMcG has served on advisory boards for Boehringer Ingelheim, J&J, and Novo Nordisk; received grants for educational work from AstraZeneca, Biogen, Boehringer Ingelheim, J&J, Janssen, Lilly, MSD, Novo Nordisk, Orexigen, and Sanofi; and received institutional research grant support from Novo Nordisk. SDP has received consulting fees or speaking honoraria from Abbott, AstraZeneca, Bausch, Boehringer Ingelheim, Dexcom, HLS, Janssen, Lilly, Merck, Novo Nordisk, and Sanofi; and research funding from Abbott, AstraZeneca, Bausch, Boehringer Ingelheim, Janssen, Lilly, Merck, Novo Nordisk, and Sanofi. KHP is a consultant, advisory board member, speaker, and clinical investigator for Novo Nordisk, and has received funding from the Novo Nordisk Foundation. DR is a consultant, advisory board member, speaker, clinical investigator for, and shareholder of Novo Nordisk; a clinical investigator for AstraZeneca and Boehringer Ingelheim; has received research funding from Obesinov; and received honoraria from Medscape. RLB has consulted for Boehringer Ingelheim, Novo Nordisk, and Pfizer; participates in advisory boards for ViiV and Gila Therapeutics; and participates in speaker bureau for Novo Nordisk, ViiV, and International Medical Press., (Copyright © 2021 Elsevier Ltd. All rights reserved.)