1. 18 to 75 years of age (both inclusive) at the time of signing the informed consent form (ICF).

2. History of failing to lose sufficient weight with lifestyle/dietary modification.

BMI ≥30.0 kg/m2, or

BMI ≥27.0 kg/m2 with at least 1 of the following:

4. In the investigator's opinion, are well motivated, capable, and willing to:

Exclusion Medical Conditions Related to Obesity

1. A self-reported change (increase or decrease) in body weight >5 kg within 3 months prior to screening.

2. Prior or planned surgical treatment for obesity (excluding liposuction or abdominoplasty, if performed >1 year prior to screening).

3. Have or plan to have endoscopic and/or device-based therapy for obesity or have had device removal within the last 6 months prior to screening, including but not limited to:

4. History of type 1 or T2DM, history of ketoacidosis, or hyperosmolar state/coma.

5. At least 1 laboratory value suggestive of diabetes during screening, including 1 or more of HbA1c ≥6.5% (48 mmol/mol), fasting serum glucose ≥126 mg/dL (7.0 mmol/L), or random glucose ≥200 mg/dL (11.1 mmol/L).

Other Medical Conditions

6. Renal impairment measured as estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2, calculated by chronic kidney disease-epidemiology collaboration (CKD-EPI) as determined by central laboratory during screening.

7. Known clinically significant gastric emptying abnormality (eg, severe gastroparesis or gastric outlet obstruction) or chronically take drugs that directly affect GI motility.

8. History of acute or chronic pancreatitis. A participant with a history of acute pancreatitis caused by gallstones may be included in the study if the participant has a cholecystectomy to resolve the problem.

9. Thyroid-stimulating hormone (TSH) outside of the range of 0.4 to 6.0 mIU/L at screening.

Note: Participants receiving treatment for hypothyroidism may be included, provided their thyroid hormone replacement dose has been stable for at least 6 months.

Note: TSH values above the normal range can, in some participant, suggest subclinical hypothyroidism. If, in the investigator's opinion, the participant has subclinical hypothyroidism and may require initiation of thyroid hormone replacement during the study, the participant should be excluded from the study.

10. Obesity induced by other endocrinologic disorders (eg, Cushing's syndrome) or diagnosed monogenetic or syndromic forms of obesity (eg, melanocortin 4 receptor deficiency or Prader-Willi syndrome).

11. History of significant active or unstable major depressive disorder (MDD) or other severe psychiatric disorder (eg, schizophrenia, bipolar disorder, or other serious mood or anxiety disorder) within the last 2 years.

Note: Participants with MDD or generalized anxiety disorder whose disease state is considered stable for the past 2 years and expected to remain stable throughout the course of the study, in the opinion of the investigator, may be considered for inclusion if they are not on excluded medications.

12. A history of suicide attempt.

13. Patient health questionnaire-9 (PHQ-9) score of 15 or more at screening.

14. On the Columbia Suicide Severity Rating Scale (C-SSRS) prior to randomization:

15. Uncontrolled hypertension (SBP ≥160 mmHg and/or DBP ≥100 mmHg). If a participant is on antihypertensive therapies, doses must be stable for 30 days prior to screening. For participants with uncontrolled hypertension at screening, antihypertensive medication may be started or adjusted. BP must meet the protocol criterion for hypertension control with stable treatment for at least 30 days before re-screening.

16. An elevated resting pulse rate >100 bpm at baseline.

17. Any of the following cardiovascular conditions within 3 months prior to screening:

18. Ongoing or history of frequent intermittent or chronic tachyarrhythmia syndromes (eg, atrial fibrillation, supraventricular tachycardia, and positional orthostatic tachycardia syndrome).

Note: Participants with a history of premature atrial contractions or premature ventricular contractions may be included.

19. NYHA Functional Classification III or IV CHF.

20. An electrocardiogram (ECG) considered by the investigator indicative of active cardiac disease or with abnormalities that may interfere with the interpretation of changes in ECG intervals at screening.

21. Acute or chronic hepatitis, or signs and symptoms of any other liver disease other liver disease except nonalcoholic fatty liver disease (NAFLD) (ie, participants with NAFLD are eligible for participation), or any of the following at screening:

22. Serum calcitonin level of:

23. A family or personal history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN2).

24. A history of an active or untreated malignancy or are in remission from a clinically significant malignancy (other than basal or squamous cell skin cancer, in situ carcinomas of the cervix, or in situ prostate cancer) for <5 years.

25. Any other condition not listed in this section (eg, hypersensitivity or intolerance) that is a contraindication to GLP-1R agonists.

26. A history of any other condition (such as known drug or alcohol abuse, diagnosed eating disorder, or other psychiatric disorder) that, in the opinion of the investigator, may preclude the participant from following and completing the protocol.

27. Alcohol consumption >14 units/week for women and >21 units/week for men.

28. A history of use of marijuana or tetrahydrocannabinol (THC)-containing products within 3 months of enrollment or unwillingness to abstain from marijuana or THC-containing product use during the study.

Note: If a participant has used cannabidiol oil during the past 3 months but agrees to refrain from use for the duration of the study, the participant may be enrolled.

29. Have had an organ transplant (corneal transplants [keratoplasty] are allowed) or are awaiting an organ transplant.

30. Any hematological condition that may interfere with HbA1c measurements (eg,

31. A blood donation of ≥500 mL within the previous 8 weeks of screening or a blood transfusion or severe blood loss within the prior 3 months, or have known hemoglobinopathy, hemolytic anemia, sickle cell anemia, or a hemoglobin value <11 g/dL (men) or <10 g/dL (women), or any other condition known to interfere with HbA1c methodology.

32. A history of atopy (severe or multiple allergic manifestations) or clinically significant multiple or severe drug allergies, intolerance to topical corticosteroids, or severe posttreatment hypersensitivity reactions (including, but not limited to, erythema multiforme major, linear immunoglobulin A dermatosis, toxic epidermal necrolysis, anaphylaxis, angioedema, or exfoliative dermatitis).

33. A fasting serum triglyceride level of >500 mg/dL at screening. If a participant is on lipid-lowering therapies, doses must be stable for 30 days prior to screening.

Prior/Concomitant Therapy

34. Are receiving or have received within 3 months prior to screening chronic (>2 weeks) systemic glucocorticoid therapy (excluding topical, intraocular, intranasal, single intraarticular injection, or inhaled preparations) or have evidence of a significant, active autoimmune abnormality (eg, lupus or rheumatoid arthritis) that has required (within the last 3 months) or is likely to require, in the opinion of the investigator, concurrent treatment with systemic glucocorticoids (excluding topical, intraocular, intranasal, intraarticular, or inhaled preparations) during the course of the study.

35. Receiving treatment with or have a history of treatment with (within 3 months prior to screening) medications that may cause significant weight gain including, but not limited to, tricyclic antidepressants, atypical antipsychotics, and mood stabilizers:

Examples:

36. Have taken within 3 months prior to screening medications (prescribed or over thecounter) or alternative remedies intended to promote weight loss.

Examples include, but are not limited to:

37. Use of metformin or any other glucose-lowering medication, whether prescribed for polycystic ovarian syndrome or diabetes prevention is not permitted.

38. Have started implantable or injectable contraceptives (such as Depo Provera®) within 18 months prior to screening.

Prior/Concurrent Clinical Study Experience

39. Have known allergies to GLP-1R agonists or GZR18.

40. Are currently enrolled in any other clinical study involving an IP or any other type of medical research judged not to be scientifically or medically compatible with this study.

41. Within the last 30 days, participated in a clinical study and received treatment, whether active or placebo. If the study involved an IP, 5 half-lives or 30 days, whichever is longer, should have passed.

42. Have previously completed or withdrawn from this study or any other study investigating GZR18 and have previously received GZR18.

Other Exclusions

43. Women of childbearing potential (WOCBP) who: