This legislation seeks to remove the long-standing exclusion of services provided in Institutions for Mental Diseases (IMDs) from federal Medicaid matching funds. It specifically amends the Social Security Act to eliminate language that prevents Medicaid from covering medical assistance for patients receiving care in IMDs. Furthermore, the bill strikes all references to age-based exclusions, thereby allowing Medicaid to cover IMD services for beneficiaries of all adult ages , not just those under or over 65 as previously implied in some contexts. This change aims to expand access to mental health and substance use disorder treatment under Medicaid. To ensure quality of care, the bill also redefines what constitutes an IMD under the Social Security Act. It mandates that such institutions must meet nationally recognized, evidence-based standards for mental health programs. For IMDs providing substance use disorder treatment, they must also adhere to similar evidence-based standards, such as those from the American Society of Addiction Medicine. These standards, which must be approved by the Secretary, will cover aspects like the types of services offered, hours of clinical care, and staffing credentials.