This final rule modifies the TRICARE regulation to reduce administrative barriers to access to mental health benefit coverage and to improve access to substance use disorder (SUD) treatment for TRICARE beneficiaries, consistent with earlier Department of Defense and Institute of Medicine recommendations, current standards of practice in mental health and addiction medicine, and governing laws. This rule has four main objectives: (1) To eliminate unnecessary quantitative and non-quantitative treatment limitations on SUD and mental health benefit coverage and align beneficiary cost-sharing for mental health and SUD benefits with those applicable to medical/surgical benefits; (2) to expand covered mental health and SUD treatment under TRICARE, to include coverage of intensive outpatient programs and treatment of opioid use disorder; (3) to streamline the requirements for mental health and SUD institutional providers to become TRICARE authorized providers; and (4) to develop TRICARE reimbursement methodologies for newly recognized mental health and SUD intensive outpatient programs and opioid treatment programs.