Effect of LY3437943 Versus Placebo in Participants Who Have Obesity or Are Overweight

Inclusion Criteria: * Age 18 to 75 years (inclusive) at time of informed consent. * BMI ≥30 and ≤50 kg/m², OR BMI ≥27 and \<30 kg/m² with at least 1 weight-related comorbidity (hypertension; dyslipidemia; or cardiovascular disease such as ischemic CVD or NYHA Class I-II heart failure). * Motivated and able/willing to self-inject (or have trained assistance if needed) and follow study procedures, including lifestyle advice and questionnaires. * Subgroup (NAFLD addendum): liver fat content ≥10% by MRI-PDFF (for participants invited to the addendum). * Male and/or female; contraception requirements apply; women of childbearing potential must have negative pregnancy tests at specified visits and should not be breastfeeding. * Capable of giving signed informed consent and complying with protocol requirements. Exclusion Criteria: * History of diabetes mellitus (type 1 or type 2), ketoacidosis, or hyperosmolar state/coma. * Screening lab values suggestive of diabetes (HbA1c ≥6.5%; fasting glucose ≥126 mg/dL; or random glucose ≥200 mg/dL). * Self-reported change in body weight \>5 kg within 3 months prior to screening. * Prior or planned surgical treatment for obesity (exceptions: liposuction/abdominoplasty \>1 year prior). * Current/planned endoscopic or device-based obesity therapy, or device removal within last 6 months (e.g., intragastric balloon, gastric artery embolization). * Renal impairment: eGFR \<45 mL/min/1.73 m² (CKD-EPI) at screening. * Clinically significant gastric emptying abnormality (e.g., severe gastroparesis) or chronic drugs affecting GI motility. * History of acute or chronic pancreatitis (exception for resolved gallstone pancreatitis post-cholecystectomy). * TSH outside 0.4 to 6.0 mIU/L at screening (with protocol-defined exceptions). * Obesity due to other endocrine disorders (e.g., Cushing's) or monogenic/syndromic obesity (e.g., Prader-Willi). * Psychiatric exclusion criteria including unstable major depressive disorder/severe psychiatric disorder within 2 years; lifetime suicide attempt; PHQ-9 score ≥15; or specified Columbia-Suicide Severity Rating Scale (C-SSRS) findings within past month. * Uncontrolled hypertension (systolic ≥160 mmHg and/or diastolic ≥100 mmHg) or elevated resting pulse rate (\>100 bpm) at baseline. * Recent (within 3 months) major cardiovascular events (e.g., MI, stroke, unstable angina, CHF hospitalization); tachyarrhythmia syndromes; NYHA Class III-IV CHF; or ECG abnormalities interfering with interpretation. * Acute/chronic hepatitis or liver disease other than NAFLD; or screening labs: ALT \>3× ULN, ALP \>1.5× ULN, or total bilirubin \>1.5× ULN (with exception). * Elevated calcitonin at Visit 1 per protocol thresholds; personal/family history of medullary thyroid carcinoma or MEN2. * Active/untreated malignancy or remission \<5 years (with protocol exceptions for certain in-situ/skin cancers). * Contraindication to GLP-1 receptor agonists, or other conditions that could prevent protocol compliance (including drug/alcohol abuse or eating disorder), per investigator judgment. * Alcohol consumption \>14 units/week (women) or \>21 units/week (men). * Recent marijuana/THC-containing product use within 3 months or unwillingness to abstain during trial (protocol exception for cannabidiol oil if agrees to refrain). * Organ transplant history (except corneal transplant) or awaiting transplant. * Hematologic conditions interfering with HbA1c measurement; recent large blood donation/transfusion/severe blood loss; hemoglobin below protocol thresholds. * Severe atopy/multiple severe allergies or severe hypersensitivity reactions. * Fasting triglycerides \>500 mg/dL at screening (with stability requirement for lipid-lowering therapy). * Significant active, uncontrolled medical condition or history posing risk or interfering with data interpretation, per investigator judgment. * History of symptomatic gallbladder disease within past 2 years (protocol-defined exceptions after cholecystectomy). * History of documented HIV infection. * Chronic systemic glucocorticoid therapy within 3 months or active autoimmune abnormality likely to require systemic steroids during study (with specified formulation exceptions). * Recent medications that may cause significant weight gain (e.g., tricyclic antidepressants, atypical antipsychotics, mood stabilizers) within 3 months. * Recent use (within 3 months) of medications or remedies intended to promote weight loss (examples listed in protocol, including GLP-1 RAs). * Use of metformin or other glucose-lowering medications (e.g., for PCOS or diabetes prevention) not permitted at entry. * Started implantable/injectable contraceptives within 18 months prior to screening (IUDs allowed if used ≥3 months). * Known allergies to GLP-1 receptor agonists or LY3437943. * Currently enrolled in another investigational study or recent participation/treatment within 30 days (or 5 half-lives, whichever longer). * Previously received LY3437943 in this or another study. * Investigator site personnel directly affiliated with the study and/or their immediate family; or Lilly employees. * Note: The publicly posted protocol references additional exclusion criteria numbered 52-57 in a separate protocol addendum (not included in the posted protocol PDF).