This is a Phase 1, randomized, double-blind, placebo-controlled, single-center study designed to evaluate the safety, tolerability, and pharmacokinetics of ZT003 following subcutaneous administration in healthy adult participants. The study includes both single ascending dose (SAD) and multiple ascending dose (MAD) parts.

This is a first-in-human, Phase 1, randomized, single-center, double-blind, placebo-controlled study to evaluate the safety, tolerability, and pharmacokinetics of ZT003 following subcutaneous administration in healthy adult participants. The study is designed in two parts:

Part A (Single Ascending Dose [SAD]): Approximately 40 participants will be enrolled into sequential dose cohorts. Each cohort will receive a single dose of ZT003 or matching placebo administered subcutaneously. Dose escalation will proceed based on safety, tolerability, and pharmacokinetic data from the preceding cohorts.

Part B (Multiple Ascending Dose [MAD]): Approximately 36 participants will be enrolled into sequential cohorts. Each participant will receive multiple subcutaneous doses of ZT003 or placebo. Dosing frequency and duration will be based on data obtained from Part A and guided by predefined criteria.

The study will evaluate safety through the monitoring of adverse events, clinical laboratory tests, vital signs, physical examinations, ECGs, and injection site assessments. Pharmacokinetic parameters will be measured using plasma drug concentration profiles. The results from this study will inform dose selection and design for future clinical studies in patient populations.

Inclusion Criteria:

1. Healthy male and female participants, aged 18 to 65 years at the time of screening.
2. Body weight >50 kg to <130 kg, and BMI between 22.0 and 45.0 kg/m square.
3. Medically healthy, with no clinically significant abnormalities in medical history, physical examination, vital signs, ECG, or clinical laboratory assessments, as judged by the Investigator.
4. Females of childbearing potential must use highly effective contraception and have a negative pregnancy test at screening and Day -1.
5. Male participants must agree to use acceptable contraception from screening through at least 90 days after the last dose.
6. Able to understand and comply with study procedures and provide written informed consent.
7. Thyroid function tests within normal range as specified by the testing laboratory, unless deemed not clinically significant by the PI or designee.

Exclusion Criteria:

1. History or presence of any clinically significant disease or disorder that may put the participant at risk or interfere with study assessments.
2. Positive test for hepatitis B surface antigen (HBsAg), hepatitis C antibody (HCV Ab), or HIV antibody at screening.
3. History of drug or alcohol abuse within 12 months prior to screening.
4. Use of prescription drugs, over-the-counter medications, herbal products, or supplements within 14 days (or 5 half-lives) prior to first dose unless deemed acceptable by the Investigator.
5. Participation in another clinical study with an investigational product within 30 days or 5 half-lives of the investigational product before dosing.
6. Any history of significant allergy or hypersensitivity to any component of the investigational medicinal product (IMP).
7. Clinically significant ECG abnormalities, including QTc >450 ms (males) or >470 ms (females) at screening.
8. Abnormal clinical laboratory results at screening considered clinically significant by the Investigator.
9. History of bleeding disorders or current use of anticoagulant therapy.
10. Pregnant or lactating females, or females planning to become pregnant during the study period.