Medicaid | Eligibility, Coverage & ACA Expansion

Medically reviewed by James Whitfield, MHA, CHC
Healthcare Policy & Insurance Editor · Last reviewed January 2025

Medicaid is the joint federal-state health insurance program providing coverage to low-income Americans — including children, pregnant women, elderly individuals, and people with disabilities. As of 2023, Medicaid covers approximately 89 million individuals, making it the largest health insurance program in the United States by enrollment. Medicaid is jointly funded by the federal government and states, with states operating their programs within federal guidelines.

ACA Medicaid Expansion

The Affordable Care Act included a provision expanding Medicaid eligibility to most adults under age 65 with incomes up to 138% of the federal poverty level (approximately $20,100 for an individual in 2024). As of 2024, 40 states and DC have adopted Medicaid expansion. In expansion states, the ACA has dramatically increased insurance coverage for individuals with substance use disorders and mental health conditions — populations that previously had extremely high uninsurance rates.

What Medicaid Covers

Federal law requires state Medicaid programs to cover certain mandatory benefits, including inpatient and outpatient hospital services, physician services, laboratory and X-ray services, home health services, and nursing facility services. States may also offer optional benefits including prescription drugs (covered by nearly all states), physical therapy, dental care, and behavioral health services beyond the federal minimum.

Behavioral Health Coverage Under Medicaid

Medicaid covers substance use disorder treatment and mental health services in all states, though the scope and delivery model varies. The Medicaid EPSDT benefit requires comprehensive behavioral health screening and treatment for children and adolescents. For adults, the Mental Health Parity and Addiction Equity Act (MHPAEA) applies to Medicaid managed care plans, requiring that behavioral health benefits be comparable to medical/surgical benefits. Most states cover MAT for opioid use disorder under Medicaid, including buprenorphine and methadone, though coverage of methadone through OTPs specifically varies by state.

Applying for Medicaid

Medicaid applications can be submitted through your state Medicaid agency, through HealthCare.gov (which screens for Medicaid eligibility), or in person at your local Medicaid office. Coverage can be retroactive for up to three months prior to application in some states — important for individuals who incurred medical expenses before applying.