Expiring patents for blockbuster antipsychotic medications is expected to increase use of the drugs’ generic versions and save Medicaid billions of dollars annually, a new study shows.

In 2011, five branded drugs accounted for 90% of all Medicaid spending on antipsychotics. Patents for several second-generation antipsychotics, including those five — aripiprazole (Abilify), quetiapine (Seroquel), olanzapine (Zyprexa), ziprasidone (Geodon) and paliperidone (Invega) — have expired or are set to expire within the next few years.

The patent expirations mean Medicaid payments for antipsychotics will decrease by almost $1.8 billion, roughly 50%, by 2016, the University of Maryland School of Medicine researchers predict. By 2019 those payments will decrease by $2.8 billion, or 76%. The authors suggest this decrease may help patients struggling to afford the medications, and allow policy makers to lift Medicaid restrictions on the medications. Among those restrictions are rules requiring physicians to obtain prior authorization before writing a prescription, and requirements to prescribe patients certain drugs before trying others.

Medicaid is currently the highest payer for for antipsychotic medications in the United States, accounting for 70% to 80% of all antipsychotic prescriptions.