Post-imprisonment health service contacts for mental health and substance use : a retrospective population-based data linkage study

Background: Mental health (MH) and substance use (SU) problems among people released from prison contribute substantially to premature mortality and emergency services demand. Understanding of MH- and SU-related healthcare contacts prior to these severe and costly outcomes is limited. We assessed MH- and SU-related contact rates across multiple services, comparing people released from prison to a matched general population sample. Objectives: To compare rates of health service contacts for mental health and substance use between people released from prison and a matched general population sample. Design: Retrospective cohort study using linked administrative data with nationwide coverage. The cohort contained all people released from any Scottish prison in 2015 (exposed group), and a random general population sample matched (ratio 1:5) on sex, age, postcode, and deprivation indices, who had no imprisonment in the five years prior (unexposed group). We linked individual-level administrative healthcare (prescriptions, outpatient, inpatient, emergency: 2010-2020), prison (admissions/releases: 2010-2020), and deaths records (2015-2020). We estimated adjusted incidence rate ratios (aIRRs) with 95% confidence intervals using fixed-effects Poisson regression with cluster-robust standard errors, controlling for time-in-community, pre-index MH and SU healthcare contacts, and comorbidities. We stratified models by MH, SU, and dual diagnosis (attributable to both MH and SU). Setting: Scotland. Results: We linked records for 8313 people released from prison, and 41 213 matched individuals. Contact rates were significantly higher for people released from prison across all services, and particularly for emergency and unscheduled care. aIRRs for ambulance calls were MH=7.75 [5.76-10.42], SU=7.58 [5.71-10.08], dual diagnosis=8.28 [6.50-10.55]; and emergency department contacts were MH=4.88 [3.78-6.29] and SU=7.98 [5.71-11.17]. aIRRs for community prescriptions were MH=1.80 [1.67-1.94], SU=5.95 [4.83-7.32], dual diagnosis=5.33 [3.70-7.68]; SU services were 7.13 (6.00-8.48); and outpatient MH services was 2.62 (2.17-3.16). Conclusion: Despite elevated MH- and SU-related contact rates with community services, people released from prison have disproportionately high contact rates with emergency and unscheduled care. This suggests that early support is either inadequate or not accessed by those in greatest need. Improved post-release MH and SU care is vital for individual and public health.