Eligibility Details:  
        Inclusion Criteria:
          -  Men or women between the ages of 18 and 55 years old (inclusive)
          -  Without DSM 5 (The Diagnostic and Statistical Manual of Mental Disorders, Fifth
             Edition ) - Substance Related Disorders classification; in sustained remission is not
             exclusionary
          -  Able and willing to comply with the requirements of the protocol
          -  Able and willing to provide written informed consent
          -  Willing to undergo a minor surgical procedure under local anesthetic to allow for
             investigational drug administration in the subcutaneous tissue
          -  BMI inclusive of 18.5 to 30.0
          -  Have an initial weight between 45.3 and 81.6 kilograms (inclusive)
        Exclusion Criteria:
          -  Positive urine drug screen (UDS) at screening for illicit substances.
          -  Is currently on naltrexone medication.
          -  Has had a naltrexone implant in the past 24 months.
          -  Has received treatment with an extended naltrexone product (e.g. Vivitrol) in the past
             12 months.
          -  Has a condition which requires treatment with opioid based medication.
          -  Has a known hypersensitivity to naltrexone.
          -  Has a known hypersensitivity to poly-lactic based materials e.g. biodegradable
             sutures, surgical implants or previous biodegradable implants.
          -  Has a known hypersensitivity to local anesthesia.
          -  Is prone to skin rashes, irritation or has a skin condition such as recurrent eczema
             that is likely to impact the implant site area, or as determined by the evaluating
             physician.
          -  Demonstrates any abnormal skin tissue in the proposed implantation area.
          -  Is pregnant or planning to be. Women need to have negative blood pregnancy test at
             screening. Women need to agree to practice dual contraceptives.
          -  Participant is breastfeeding or planning to be.
          -  Has a current significant neurological (including cognitive and psychiatric
             disorders), hepatic, renal, endocrine, cardiovascular, gastrointestinal, pulmonary,
             hematological or metabolic disease unless currently controlled and stable with
             protocol-allowed medication 30 days prior to proposed investigational product
             administration.
          -  Any clinically important abnormal finding as determined by medical history, physical
             examination, ECG or clinical laboratory tests.
          -  Any additional condition(s) that in the investigator's opinion would prohibit the
             participant from completing the study or would not be in the best interest of the
             participant.
          -  Alanine aminotransferase (ALT) or aspartate transaminase (AST) > 3 times the upper end
             of the laboratory normal range.
          -  Any methadone use 14 days prior to screening, and up to Study Day 0.
          -  Current DSM-5 diagnosis of schizophrenia, bipolar, anxiety, or depressive disorder,
             confirmed by the MINI diagnostic interview assessment, or currently treated with
             medications for anxiety or depression. Past history (in remission DSM-5
             classification) of anxiety or depression is not exclusionary.
          -  Any elevated risk for suicide measured using the Columbia Suicide Severity Rating
             Scale, endorsing any of the items in the past month (C-SSRS, Lifetime)
          -  Is participating or intending to participate in any other clinical trial during the
             duration of this study.