A Study to Evaluate the Effectiveness and Safety of the Drug AZD6234 for Managing Weight in Adults Who Are Obese or Overweight. These Participants May or May Not Also Have Type 2 Diabetes

Inclusion Criteria: * Aged 18 years or older at the time of signing informed consent. * Body mass index: * at least 28 kg/m²; or * at least 24 kg/m² and less than 28 kg/m² with at least one protocol-defined weight-related comorbidity, including type 2 diabetes mellitus, hypertension, dyslipidaemia, obstructive sleep apnoea, cardiovascular disease, heart failure, chronic kidney disease, metabolic dysfunction-associated steatotic liver disease, knee osteoarthritis, or stress urinary incontinence. * Stable body weight (≤ 5% body weight change) for at least 3 months prior to Randomisation. * Participants with type 2 diabetes mellitus must: * have been diagnosed at least 6 months before informed consent; * have HbA1c between 6.0% and 10.0% at Screening; and * be managed with diet and exercise alone or with a stable dose of 1 to 3 oral glucose-lowering medications for at least 3 months before Screening. * At least one previous self-reported unsuccessful attempt to lose body weight. * Participants of childbearing potential must comply with protocol-defined highly effective contraception requirements and have negative pregnancy tests at Screening and Randomisation. * Able to provide signed informed consent. Exclusion Criteria: * Obesity primarily caused by another endocrine disorder. * Severe heart failure, defined as New York Heart Association Class IV, or hospitalisation for heart failure within 3 months before Screening. * Type 1 diabetes mellitus or ketoacidosis or hyperosmolar coma/state within 3 months before Screening. * Clinically significant gastric-emptying abnormality requiring treatment. * Significant inflammatory bowel disease or another severe disease or prior surgery affecting the upper gastrointestinal tract. * Cardiovascular event, percutaneous coronary intervention, or coronary artery bypass graft within 3 months before Screening. * Previous or planned surgical treatment for obesity. * Uncontrolled hypothyroidism or hyperthyroidism. * Significant hepatobiliary disease, including protocol-defined elevations in alanine aminotransferase, aspartate aminotransferase, or total bilirubin. * Neoplastic disease within 5 years before Screening, except as otherwise permitted by the protocol. * Clinically important disease or disorder that may place the participant at risk or interfere with study participation. * Known or suspected drug abuse or alcohol abuse. * Planned elective surgery requiring discontinuation of study intervention for more than 6 weeks. * Weight-management treatment within 3 months before Randomisation. * Treatment with a glucagon-like peptide-1 receptor agonist or another glucagon-like peptide-1-containing medication within 3 months before Randomisation. * Treatment with a marketed or investigational amylin-based compound within 3 months before Randomisation. * Use of insulin therapy for type 2 diabetes mellitus. * Long-term systemic glucocorticoid treatment lasting more than 14 days or use of central nervous system stimulants. * Concomitant medication that may increase risk, affect study results, or interfere with study participation. * Unstable major depressive disorder or Patient Health Questionnaire-9 score of 15 or higher. * History of psychosis or active symptomatic bipolar disorder. * Active suicidal ideation corresponding to Category 4 or 5 on the Columbia-Suicide Severity Rating Scale, or history of a suicide attempt. * Participation in another clinical study within 30 days before Screening. * Known hypersensitivity to AZD6234. * Involvement in the planning and/or conduct of the study. * Unlikely or unable to comply with study procedures, restrictions, or requirements. * Previous randomisation in the present study. * Currently pregnant or breastfeeding. * Any other condition that, in the Investigator's judgement, makes participation inappropriate.