Naltrexone, an opioid receptor antagonist, is one of only three medications approved by the FDA to treat opioid use disorder (OUD). Use of naltrexone is presently limited to specialized addiction treatment settings, in part because of the few training opportunities for medical providers on the use of naltrexone. This module presents a summary of a 4-modules training program on the use of naltrexone developed by PCSS. It reviews background information on the use of opioid antagonists in treatment of OUD, describes differences between agonist and antagonist based treatment, and provides a summary of the evidence for its efficacy. Clinical issues are also discussed including the selection of patients, protocols for treatment initiation, and the management of common clinical challenges that emerge during maintenance treatment with naltrexone.