We study the effect of public insurance on smoking cessation medication prescriptions and financing. We leverage variation in insurance coverage generated by recent Affordable Care Act expansions to Medicaid. We estimate differences-in-differences models using administrative data on the universe of Medicaid-financed prescriptions sold in retail and online pharmacies 2011-2017. Our findings suggest that these expansions increased Medicaid-financed smoking cessation prescriptions by 34%. This increase reflects new medication use and a shift in payment from private insurers and self-paying patients to Medicaid. Adjusting our estimate for changes in financing implies that Medicaid expansion lead to a 24% increase in new medication use.