1. Short title This Act may be cited as the Increasing National Patient Access To Improved Effective Necessary Mental Health Treatment Act of 2018 or the INPATIENT Act of 2018 . 2. Demonstration project waiving IMD exclusion to expand access to inpatient psychiatric services under the Medicaid program (a) Authority To conduct demonstration project (1) In general The Secretary of Health and Human Services (in this Act referred to as the Secretary ) shall establish a demonstration project (in this Act referred to as the demonstration project ) to test the impact of waiving the limitation of subdivision (B) following paragraph (29) of section 1905(a) of the Social Security Act ( 42 U.S.C. 1396d(a) ) on average length of stay, readmissions, cost, and quality outcomes for inpatient psychiatric hospital services and substance abuse services. (2) Terms Under the demonstration project, an eligible State (as defined in subsection (b)) shall provide payment under its State Medicaid plan under title XIX of the Social Security Act to qualifying institutions (as defined in subsection (b)(3)(C)) for the provision of medical assistance available under such plan to individuals who— (A) have attained age 21, but have not attained age 65; (B) are eligible for medical assistance under such plan (or under a waiver of such plan); (C) require such medical assistance for inpatient psychiatric hospital services or residential substance abuse services