Inclusion Criteria:
1. Male or female, of any race, between 18 and 60 years of age, inclusive.
a. Females must not be pregnant or lactating.
2. Body mass index between 25.0 and \<40.0 kg/m\^2.
3. Have a stable body weight (\<5 kg self-reported change) within 3 months before screening, as assessed by the investigator (or designee) based on participant self-report.
Exclusion Criteria:
1. History or evidence, at screening or check-in, of clinically significant disorder, condition, or disease not otherwise excluded that, in the opinion of the investigator (or designee), would pose a risk to participant safety or interfere with the trial evaluation, procedures, or completion. Participants with clinically significant findings from medical history, physical examination, 12-lead electrocardiogram (ECG), vital signs measurements, and clinical laboratory evaluations (congenital nonhemolytic hyperbilirubinemia \[eg, suspicion of Gilbert's syndrome based on total and direct bilirubin\] is not acceptable) as assessed by the investigator (or designee) will be excluded.
2. History of or active diabetes (regardless of type, with the exception of a history of gestational diabetes) or hemoglobin A1C ≥6.5% (≥48 mmol/mol).
3. History or evidence of endocrine disorder (eg, Cushing's Syndrome) that can cause obesity.
4. History of acute or chronic pancreatitis within 1 year prior to check-in, or elevation in serum lipase/amylase (\>2 x the upper limit of normal) at screening or a fasting serum triglyceride level of \>500 mg/dL at screening.
5. Malignancy, except nonmelanoma skin cancers or cervical or breast ductal carcinoma in situ, within the last 5 years.
6. Personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2.
7. History or current signs or symptoms of cardiovascular disease (aside from controlled hypertension and controlled dyslipidemia), including but not limited to myocardial infarction, congenital heart disease, valvular heart disease, coronary revascularization, or angina.
8. History or evidence of clinically significant arrhythmia at screening, including any clinically significant findings on the ECG taken at screening or check-in.
9. History of hypersensitivity, intolerance, or allergy to AMG 133 or related/similar compounds or their ingredients.
10. Estimated glomerular filtration rate ≤60 mL/min/1.73 m\^2, as calculated by the Chronic Kidney Disease Epidemiology (CKD EPI) equation at screening or check-in.
11. Use of any over-the-counter or prescription medications within 30 days or 5 half-lives (whichever is longer) before check-in.
12. Current use or prior use of any glucagon-like peptide-1 receptor (GLP-1R) agonist, or gastric inhibitory polypeptide receptor (GIPR) agonist or antagonist within the past 3 months prior to check-in.
13. Current or prior use of all herbal medicines (eg, St. John's wort), vitamins, and supplements consumed by the participant within the 30 days prior to enrollment, unless deemed acceptable by the investigator (or designee) and in consultation with the medical monitor, as appropriate.
14. Participant has received a dose of an investigational drug within the past 30 days or 5 half-lives, whichever is longer, prior to check-in.
15. Have previously completed or withdrawn from this trial or any other trial investigating AMG 133 or have previously received the investigational product.
