Single Ascending Dose Study of NRS 033 in Healthy Volunteers

Inclusion Criteria: * Male or female ≥18 and ≤55 years of age at time of consent * Body mass index ≥18.0 to ≤35.0 kg/m2 * Medically healthy based on the absence of clinically significant abnormal vital sign * Females must have a negative serum pregnancy test at time of screening and negative urine pregnancy test upon admission; also, females of childbearing potential must agree to use a highly effective means of contraception from Screening until 9 months after receiving the study medication. * Male subjects with female partners of childbearing potential must agree to use a male condom and will be advised of the benefit for a female partner to use a highly effective method of contraception * Agree to stay within National Institute on Alcohol Abuse and Alcoholism (NIAAA) low risk drinking criteria. For women, low-risk drinking is no more than 3 drinks on any single day and no more than 7 drinks per week. For men, it is defined as no more than 4 drinks on any single day and no more than 14 drinks per week. * Agree not to take opioid analgesics. Exclusion Criteria: * Clinically significant medical or psychiatric diagnosis (assessed on history, physical exam, ECG, and/or blood tests; includes significant history of cardiovascular, pulmonary, hepatic, gallbladder, or biliary tract, renal, hematologic, gastrointestinal, endocrine, immunologic, dermatologic, neurologic, psychiatric disease, or active sexually transmitted disease). * Significant neuropsychiatric diagnosis (e.g., major depression, suicidal ideation, multiple sclerosis, dementia) as reported by the subject, or a past history of suicide attempt. * Females who are pregnant, lactating, or likely to become pregnant during the study. * History over last 30 days of consuming alcohol \>3 drinks day per day or \>7 drinks per week if female; if male \>4 drinks per day or \>14 drinks per week. * Currently uses tobacco or nicotine containing products, including but not limited to cigarettes, electronic cigarettes, pipes, cigars, chewing tobacco, nicotine patch or nicotine gum. * Reported history of a significant traumatic injury, major surgery, or open biopsy within the 4 weeks prior to signing the informed consent form. * Subject reported history of any use of long-term use of opioids agonists or antagonists; e.g., methadone, oxycodone, hydrocodone, naltrexone, buprenorphine. * Subject reported history of any medications to treat opioid use disorder (MOUD); e.g., methadone, naltrexone, buprenorphine, kratom. * Subject reports anticipated need for opioid analgesia in the next 12 months (e.g., planned surgery). * Subject reports history or presence of allergic or adverse response (including rash or anaphylaxis) to naloxone, naltrexone, nalmefene, morphinan opioid agonists, benzyl alcohol or sesame oil. * Positive urine drug screen (UDS) for barbiturates, benzodiazepines, cocaine, methamphetamine, or opioids. * Positive alcohol breath test. * Received an investigational drug within the last 30 days or 5 half-lives of the drug, whichever is longer, prior to administration of study medication. * Has taken exclusionary prohibited medications within the last 30 days or 5 half-lives of the drug, whichever is longer. * Subjects with a history of syncope, or have a history of symptomatic hypotension or symptomatic hypoglycemia. * Subjects who test positive for human immunodeficiency virus (HIV), Hepatitis B surface antigen (HbsAg), or Hepatitis C virus (HCV) antibody.