In the vast majority of the United States, prisons and jails are the most common place to find people suffering from mental illness. But a new Human Rights Watch (HRW) report reveals that most U.S. correctional facilities are underequipped to deal with mental health needs and are inflicting serious harm on this vulnerable population, Al Jazeera America reports.

The HRW report is the first-ever comprehensive study on the mistreatment and abuse of mentally ill inmates across the country. The findings estimated that one in five U.S. inmates show signs of serious mental illness, and many more experience less severe or intermittent symptoms while incarcerated.

After traveling to prisons across the country, HRW researchers found that a large percentage of mentally ill inmates are struggling to manage symptoms of their mental illness, either from a lack of medication, counseling or both. This absence of comprehensive mental health treatment is often compounded by a lack of training among correctional staffers to either identify or manage the behaviors of mental illness.

The report documented numerous episodes of corrections officers retaliating against inmates they perceived to be “acting up” when these prisoners were actually exhibiting signs of mental illness. Advocates accused correctional staffers of regularly mistreating mentally ill inmates using excessive force, harmful chemical agents, stun guns and full-body restraints.

As a result of this abuse, HRW psychologists found that many mentally ill inmates released from U.S. correctional facilities were sicker and more socially impaired than when than they entered the system. The report also found that “warehousing” the mentally ill in U.S. prisons was by far more expensive—both socially and financially—than providing them with appropriate mental health treatment.

For more information about mental illness outcomes among newly released inmates, click here.