This is a A Phase 1, Randomized, Double-Blind, Placebo-Controlled, Single-Ascending-Dose Study To Investigate the Safety, Tolerability, and Pharmacokinetics of a kappa receptor agonist HSK21542 in Healthy Volunteers.

The study will enroll approximately 50 adults. The anticipated study duration will be up to 6 months.

Inclusion Criteria:

• Healthy male and female subjects, age 18-45 years;
• BMI between 18.0-27.0 kg/m2
• Determined by investigator to be in general good health according to medical history, comprehensive physical examination;
• Understanding of the nature, significance, potential benefits and risks of the trial, understanding of the procedures and be able to provide written informed consent voluntarily ;
• Good communication with investigators, compliance with the study requirements and willingness to stay in phase I clinical trial ward as required.

Exclusion Criteria:

• Anyone who has suffered or is currently suffering from any serious diseases, that may interfere with the results of the trial;
• Determined by investigator to be abnormal with clinical significance in Physical examination, vital signs monitoring, electrocardiogram, chest radiograph, laboratory examination;
• HBsAg positive, HCV antibody positive, Treponema pallidum antibody positive, or HIV antibody positive;
• QTcF > 450ms;
• Allergic constitution;
• Intolerance of venipuncture and/or history of haemorrhage or needle fainting;
• Drug or alcohol abuse;
• Have used any prescription, over-the-counter, Chinese herbal medicine or health products within 14 days;
• Blood donation or massive bleeding within 3 months (greater than 450 mL);
• Participants in any drug clinical trial within 3 months.
• Birth planning in the next six months.