Just like insurance companies and public health programs, prisons worry that health services might be over-used if the people they serve don't have skin in the game.  

A study by the Brennan Center for Justice at New York University finds that 38 states charge prisoners certain fees for medical services. The introduction of fees is an attempt to rein in the growing cost of prison health care on public coffers. A recent study by Pew Charitable Trusts estimated the annual cost of medical services in U.S. prisons to be $7.7 billion.  

The fee structures vary dramatically by state, reports Stateline. The study suggests that fees are typically under $20 for doctor visits and that they are often waived if the inmates say they can't afford them. However, Texas charges prisoners up to $100 for a physician visit and Utah charges inmates up to $2,000 for a hospitalization outside of prison.