The primary objective of this study is to evaluate the safety and tolerability of a single dose of ALRN-5281 administered by subcutaneous injection to healthy adult volunteers.

Inclusion Criteria:

1. Healthy male or female subjects aged 20 to 50 years, inclusive, at the time of informed consent.
2. Subjects must be in good health as determined by the Investigator based on detailed medical history, physical examination, vital signs, clinical laboratory tests, ECGs and other screening evaluations.
3. Ability to provide written informed consent and complying with all study requirements and restrictions.
4. Is a non-smoker and non-tobacco user for a minimum of 6 months prior to screening

Exclusion Criteria:

1. History or current evidence of any clinically significant cardiac, endocrinologic, hematologic, hepatobiliary, immunologic, metabolic, urologic, pulmonary, neurologic, dermatologic, psychiatric, renal, or other major disease, as determined by the Investigator
2. Previous treatment with any GH Releasing Hormone (GHRH) analog.
3. Participation in another clinical trial or treatment with an investigational agent within 30 days or 5 half-lives, whichever is longer, prior to enrollment.
4. History of cancer within the past five years (excluding non-melanoma skin cancer).
5. History of alcohol or drug abuse or dependence within 12 months of screening as determined by the Investigator.
6. Subjects with a body weight > 120 kg.