This study analyzes the effects the Affordable Care Act’s (ACA) Medicaid expansion had on mental health symptoms. Data from adults aged 18-64 years in the nationally representative Panel Study of Income Dynamics 2009-2019 waves were used in a difference-in-differences analysis to compare uninsurance, Medicaid insurance, self-reported life satisfaction, self-reported psychological distress, severe psychological distress, and health professional diagnosis depression, anxiety, and permanent memory loss. The study examines individuals in four income categories, focusing on those within 100-138% the federal poverty level in states that opted for Medicaid expansion. Key findings show a reduction of 13 percentage points in the probability of being uninsured (p=<.001), an increase of 12.6 percentage points in the probability of being covered by Medicaid (p=<.001), and a 3.4 percentage point increase self-reported life satisfaction. Men had a marginally significant 3.2 percentage point decrease in the probability of having severe psychological distress (p=<.1). There was a 1 percentage point increase in the probability of being diagnosed with depression and a 2.5 percentage point probability of an anxiety diagnoses by a health care professional (p=<.05). Self-reported psychological distress resulted in no significant change score change after the implementation of Medicaid expansion for those in the 100-138% federal poverty level. The evidence from this study implies the solution to improving mental health through public policies is complex and requires a multi-faceted approach. Further research is needed to develop a broader understanding of the impact of Medicaid expansion on mental health.