The Mental Health Infrastructure Improvement Act of 2025 authorizes the Secretary of Health and Human Services to provide loans and loan guarantees for the planning, construction, or renovation of pediatric and adult mental health and substance use disorder treatment facilities. These funds can also be used to enhance digital infrastructure, telehealth capabilities, or other patient care infrastructure, and to add or convert beds for psychiatric and substance use inpatient services. The bill includes provisions for refinancing certain existing loans, subject to specific limitations. In allocating these funds, the Secretary must prioritize projects that increase psychiatric or substance use disorder bed capacity in underserved counties or provide services in high-need rural or underresourced communities. Preference is also given to facilities offering multiple services across the care continuum or specialized care for complex cases, with at least 25 percent of funds set aside for facilities serving primarily pediatric and adolescent populations. The legislation outlines specific terms and conditions for these financial instruments, such as a maximum loan maturity of 20 years and a requirement for borrowers to finance at least 25 percent of the project from non-federal sources. Loans and guarantees are contingent on enhancing public access to services and efficient credit subsidy. The bill limits total funding to $200,000,000 annually for fiscal years 2026 through 2030, subject to appropriations. Additionally, the Act establishes the Mental Health and Substance Use Treatment Trust Fund in the U.S. Treasury. Revenues from the loan and loan guarantee program that exceed its operational costs will be deposited into this fund, which is authorized to be used for block grants supporting community mental health services.