Peer support services for individuals with substance use or mental health disorders, provided by trained peer workers with their own lived experience of recovery, have expanded rapidly within Medicaid over the past two decades. Nearly every state now covers these services, yet coverage does not ensure use. This brief examines how much Medicaid enrollees used separately billed peer support services in each state in 2018 and 2023, and what drove changes over time.

Why This Matters

Peer support services offer a promising, low-cost way to improve recovery outcomes and treatment engagement for people with substance use or mental health disorders. Policymakers, Medicaid agencies, and behavioral health advocates have invested substantially in building the payment infrastructure for these services, but if enrollees aren't using them, that infrastructure isn't delivering on its promise. Understanding why use remains low in most states, and why some have succeeded in expanding it, can help guide more effective policy and investment.

What We Found

Use of peer support services grew modestly between 2018 and 2023 but remains very low in most states.

• For substance use disorders: In 2018, only Arizona had reached established levels of use (more than 10 percent of eligible enrollees). By 2023, six states had reached that threshold, and use increased in all but three states. Kentucky had the highest use in 2023, at nearly 21 percent.
• For mental health disorders: Use increased in 27 states but declined in 14 others. No state crossed into established use between 2018 and 2023, and in most states, fewer than 2 percent of eligible enrollees received peer support services.
• Population shifts don't explain the trends. We tested whether changes in enrollees' age and disorder severity could account for observed shifts in use. They could not; the pattern of low and variable use persists even after accounting for who is in the Medicaid population.

Wide variation across states suggests that the states with growing or established use may offer replicable lessons. Policymakers can study what Arizona, Kentucky, and other higher-use states have done differently, whether in workforce development, billing practices, or outreach, and apply those lessons elsewhere.

How We Did It

We analyzed Medicaid claims and eligibility data from the Transformed Medicaid Statistical Information System for adults ages 18 to 64 with substance use or mental health disorders in 2018 and 2023. We identified peer support service use primarily through a standard billing code and a small number of state-specific codes; because billing practices vary by state, estimates may not be perfectly comparable across states. To test whether shifts in enrollees' age and disorder severity explained changes over time, we applied a statistical technique called marginal standardization in states with sufficient data.