Inclusion Criteria:
* 18 years of age or older.
* Lives within a reasonable distance from NYPH for convenient clinic visits.
* Can speak, read, and write English proficiently.
* Meet diagnostic criteria for PGD based on the DSM guidelines
* If a female patient, must agree to use a method of contraception and be willing and able to continue contraception during the first 8 weeks of the study while she is taking the study drug. Female patients who are planning to use oral hormonal contraception during this time must have initiated it at least 2 months prior to the baseline visit.
* If a male patient, must agree to use a method of contraception and be willing and able to continue contraception during the first 8 weeks of the study while he is taking the study drug.
Exclusion Criteria:
• Having recently started taking/prescribed medications for any psychiatric illness (e.g.
SSRIs for MDD) within the past 3 months; participants who have been taking this medication for longer than 3 months can be included.
* Having recently started psychotherapy for any psychiatric illness within the past 3 months; participants who have been receiving psychotherapy for longer than 3 months can be included.
* Prior history of recently active (e.g. within the past 3 months) opioid dependence.
* Current prescription, non-prescription, or illicit opioid use, (i.e., acute use within the past 14 days or chronic use within the last 30 days), including opioid antagonists for alcohol or opioid dependence, all opioid analgesics, certain cough and cold remedies (e.g., codeine), and certain anti-diarrheal preparations (e.g., loperamide).
* Possible future use of opioids during the study (e.g. for surgery).
* Current use of leflunomide (Arava), droperidol (Droleptan), diazepam (Valium), thioridazine (Mellaril, Novoridazine, Thioril), or any other clinically relevant medication that has potential to cause liver injury with concurrent use of naltrexone.
* Currently pregnant, lactating, or planning to become pregnant during the study.
* Active hepatitis or liver disease.
* Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) levels more than one standard deviation (SD) above the upper limit of normal on initial laboratory examination. Screen positive for active suicidal thoughts or behaviors.
