Change in Severity of Mental Disorder for Individuals in Custody in Short-Term Segregation.

The mental health effects of segregation remain contested, with limited longitudinal evidence using clinical data. We conducted a retrospective longitudinal observational study of individuals placed in segregation in British Columbia correctional facilities between 2019 and 2022. Global mental health severity was assessed using serial Clinical Global Impression for Corrections (CGI-C) ratings. Mixed-effects regression models were used to examine change in CGI-C scores over time, accounting for repeated observations nested within segregation encounters and individuals. The sample included 2,288 individuals across 3,273 segregation encounters (9,282 CGI-C observations). The median segregation duration was 10 days. At the encounter level, 24.6 percent showed at least a one-point improvement in CGI-C, 60.3 percent showed no change, and 15.1 percent worsened. In adjusted models, identified mental health needs (MHNs) were associated with higher overall severity (higher CGI-C scores) and a small deterioration (increase in CGI-C scores) over time. Baseline mental health severity strongly differentiated the trajectories: individuals with high initial CGI-C ratings showed a marked early reduction in severity, whereas those with low initial severity exhibited a gradual increase. Despite improvement, high-severity individuals remained more symptomatic overall. Individuals with MHNs at baseline experienced a less favorable trajectory, although persons with a higher severity at baseline modestly improved over time, perhaps because of available support services.