According to several studies, the mentally ill suffer more from solitary confinement than the non-mentally ill prisoner. Also, when compared to the rest of the inmate population, the mentally ill are more likely to end up in solitary confinement, thus creating the potential for a cyclical effect.
Research has found that diagnosed mentally ill inmates have higher suicide rates and rates of self-harm when they are exposed to the conditions of solitary confinement. Also there is the complication of delivering care to a patient who is being kept in isolation via confinement. It is simply more difficult for a care giver to access the person on an effective level.
It should be noted, however, there is not a consensus on the matter. Other researchers claim that the studies were poorly constructed and performed, and more study is needed before reaching a conclusion on the effects of solitary confinement on the mentally ill in correctional facilities.