Increasing National Patient Access To Improved Effective Necessary Mental Health Treatment Act of 2020 or the INPATIENT Act of 2020 This bill requires the Centers for Medicare & Medicaid Services (CMS) to establish programs that test the impact of expanding the coverage of certain psychiatric services under Medicaid. Specifically, the CMS must establish a demonstration program to test the impact of waiving the institutions for mental diseases (IMDs) Medicaid payment exclusion on specified metrics relating to inpatient psychiatric hospital services and substance abuse services. (Current law generally prohibits federal payment under Medicaid for services provided in IMDs for individuals under the age of 65, although states may receive payment through certain mechanisms like Medicaid demonstration waivers.) The CMS must also establish a pilot program to test the impact of eliminating the Medicare 190-day lifetime limit for inpatient psychiatric hospital services, particularly the impact on value, choice, and the alignment of inpatient mental health benefits with inpatient physical health care benefits under Medicare.