 - 1 Any psychiatric e.g. depression with suicidal ideation or medical condition that would preclude safe participation in the study; 2 known allergyprevious adverse reaction to naltrexone; 3 current use of dependence on any opioids or a known medical condition which currently requiresmay likely require opioid analgesics; 4 opioid-positive urine at enrollment; 5 current CD4 count 200 cellsmm3 6 moderatesevere liver disease AST, ALT 3 times upper limit of normal; 7 impaired renal function creatinine clearance 50 mlmin; 8 currently participating in another intervention research study with potential overlap; 9 alcohol dependence as determined by SCID criteria participants with non-dependent alcohol use disorderssymptoms of alcohol abuse per DSM-IV are eligible 10 any condition that, in the principal investigator andor study clinicians judgment interferes with safe study participation or adherence to study procedures; 11 not having a cell-phone that can send and receive text messages. 