Inclusion Criteria:
1. Is willing and able to provide informed consent and comply with all protocol requirements
2. Is aged ≥18 years and ≤55 years at time of informed consent
3. Has a body mass index (BMI) between 18.0 and 32.0 kg/m2 and body weight (BW) not lower than 50 kg
4. Participant is a nonsmoker (for at least 3 months prior to Screening) and does not use tobacco-containing products (including but not limited to cigarettes, pipes, cigars, chewing tobacco, or nicotine patch or gum)
5. Has Blood pressure (BP) and Heart rate (HR) within the normal range at the Screening visit after 5 minutes in a seated position:
1. Systolic BP between 90 and 145 mmHg
2. Diastolic BP between 60 and 90 mmHg
3. HR between 60 and 90 beats per minute
6. Electrocardiogram (ECG) is normal based on 12-lead ECG assessment at Screening:
1. ECG PR interval between 120 and 200 ms
2. ECG QRS interval \<100 ms
3. ECG QT interval (corrected) (QTc) with Fridericia formula (QTcF) \<450 ms and no history of additional risk factors for Torsades de pointes (TdP)
4. No sign of any sinus node dysfunction
7. Has clinical laboratory parameters (hematology \[including coagulation\], clinical chemistry, and urinalysis) within normal ranges. Individual values out of the normal range may be acceptable if judged clinically insignificant by an Investigator.
8. Has not been dosed in an interventional clinical drug trial within 30 days prior to screening or within 5 half-lives of the last dose of study drug, whichever is longer.
9. If female, participants who are not of childbearing potential should be surgically sterile (e.g., have undergone hysterectomy, bilateral oophorectomy, bilateral salpingectomy, or tubal ligation/occlusion) or in a post-menopausal state (at least one year without menses). Female participants of childbearing potential will use a highly effective (i.e., failure rate of \<1%) method of contraception throughout the study and for at least five half-lives following MCAM dosing. Methods of contraception that are considered to be highly effective with a failure rate of \<1% that are appropriate for this study include the following: a) intrauterine device (IUD)/intrauterine system (IUS); b) implantable rod; c) bilateral tubal occlusion; d) complete abstinence from sexual intercourse; and e) infertile male partner (e.g., vasectomized \[with documented evidence of azoospermia\], permanently sterile following bilateral orchidectomy, or any other documented cause of infertility).
10. If female, must have a negative serum or urine pregnancy test at Screening and a negative serum or urine test at Admission (day 1)
11. Male participants who report surgical sterilization will be required to confirm sterility by post-vasectomy semen analysis (PVSA). Participants in whom PVSA confirmation cannot be obtained will be required to use a double-barrier method (e.g., condom with spermicide), same as for the rest of the male participants, or agree to remain abstinent from heterosexual intercourse at the time of Screening, during the study, and for at least five half-lives following MCAM dosing.
12. If male, participants must agree not to donate sperm for the duration of the study and for 90 days after the last dose of study drug.
Exclusion Criteria:
1. Any significant acute or chronic medical illness
2. Any history of cancer within 5 years of enrollment, with the exception of fully resected skin basal cell carcinoma
3. Any major hospitalization or surgery 3 months prior to study drug administration
4. Has donated or experienced a blood loss of 500 mL or more within 56 days prior to Screening or has donated plasma within 7 days prior to Screening
5. Poor venous access assessed at Screening
6. Has ever participated or plans to participate in a substance or alcohol rehabilitation program to treat their substance or alcohol dependence. If participation in a rehabilitation program was court-mandated as part of a plea agreement, entry may be permissible at an Investigator's discretion
7. Any history of substance use disorder) as defined in the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5; e.g. a score of ≥2, within a 12-month period) or recent use of an opioid-containing product (e.g., codeine) within 6 months prior to study drug administration
8. History of, or currently diagnosed with, any clinically significant psychiatric disorder (based on the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition \[DSM-5\] and Mini International Neuropsychiatric Interview \[MINI\] criteria), which in the opinion of an Investigator could interfere with study participation or study data collection
9. History of any suicidal ideation within the past 6 months or a lifetime history of suicidal behavior, as assessed by the Columbia-Suicide Severity Rating Scale (C-SSRS)
10. Any neurological, renal, cardiac, hepatic, or other medical condition that could interfere with study assessments as determined by and Investigator, or Sponsor
11. Any significant illness or infection, as determined by an Investigator or Sponsor, within the prior 30 days
12. Positive urine alcohol or urine drug screen for substance of abuse at Screening
13. Must not be physically dependent on opioids, as demonstrated by successful completion of the naloxone challenge
14. Known hypersensitivity to any component of the MCAM drug product, naloxone, or placebo
15. Use of any prescription or over-the-counter medications (such as antacids, vitamins, minerals, dietary/herbal preparations, St. John's Wort, and nutritional supplements) within 14 days prior to Screening or 5 half-lives prior to the study
16. Positive screen for hepatitis B surface antigen (HBsAg), Hepatitis C (HCV) antibody, or HIV-1 and HIV-2 antibodies
17. Have a procedure planned that would require the use of opioids for pain management within at least 2 weeks after the conclusion of the study (participants may be resistant to opioids for two weeks or longer after study participation)
18. Is likely, in the opinion of an Investigator, to be non-compliant or uncooperative with study procedures for any reason
19. If female, are pregnant, nursing, or planning to become pregnant during the study
