A report from Peninsula College of Medicine and Dentistry, Plymouth University and the Centre for Mental Health, suggested that prison and community sentences offer the best opportunities to provide mental healthcare to help break the cycle of repeat offending, unemployment and ill health.
The study found support for offenders with mental health problems falls substantially short of the treatment available for those with addictions.
Offenders reported low levels of healthcare contact for common mental health problems and comparatively high levels of contact with specialist drug services, particularly those using heroin, the study said.
Researchers interviewed 200 offenders as they passed through police stations, courts, prison and the probation service, to document both their health needs and the care provided.
"Most prisoners, and many people on the probation caseload, have a mental health condition," Sean Duggan, chief executive of the Centre for Mental Health, said in a statement. "It is important that these people are able to get access to mental health support as part and parcel of help with their most urgent needs. This should include equal access to Improving Access to Psychological Therapies services for offenders."