Comorbid substance use disorders and mental health disorders among New Zealand prisoners

A study of New Zealand prisoners conducted by the Department of Corrections in 1999 showed that up to 70 percent had drug and/or alcohol problems and a significant proportion had various mental health issues. However, that research didn’t consider the co-existence of mental health issues and drug/alcohol  problems, which overseas studies have identified as significant among prisoners.

Offenders are screened for drug and alcohol issues and mental health problems on reception to prison but, if problems are indicated, further assessments are conducted separately and the conditions are treated in parallel or serially. Understanding the extent of comorbidity is critical to providing the best possible treatment to the prisoner population. It is acknowledged that diagnosis of comorbid drug/alcohol problems and mental health issues can be difficult, as the symptoms related to drug use and those related to mental health disorders can be confused. In addition, the symptoms related to drug taking or mental health disorders may combine and reinforce each other when they appear, making it difficult to distinguish between the two.

In 2014, the Department successfully applied for funds from the Government’s Proceeds of Crime allocation under the Methamphetamine Action Plan to conduct a study into the prevalence of co-morbid mental health and substance abuse issues amongst prisoners. National Research Bureau was contracted to interview prisoners about substance use and mental health problems, and CGA Consulting was contracted to analyse the data collected and to produce a report summarising the findings.

Over 1200 prisoners were interviewed across 13 prisons between March and July 2015 and this report presents the findings from those interviews.

The results will enable the Department to work with the Ministry of Health to improve planning for service delivery across the health and corrections domains; they will support improved delivery of forensic mental health services within prisons; and they will assist the Department in assessing prisoners and ensuring that all forms of treatment, both psychiatric and rehabilitative, are delivered in an integrated way.

Please email us if you would like a copy of this document in a different format.

Commissioning agencies
Date of last publication
Jun 2016

Methodology

This study used the Composite International Diagnostic Interview 3.0 (CIDI 3.0) and the Personality Diagnostic Questionnaire 4+ (PDQ-4) to assess the prevalence of mental health and substance use disorders. The study sample included 1209 New Zealand prisoners across 13 prisons. This report presents the prevalence for the 12-month and lifetime diagnosis of mental health and substance use disorders including breakdowns by gender, age and ethnicity. Comparisons have been provided where possible for the general population using the 2006 New Zealand Mental Health Survey (unless noted otherwise) or the 1999 New Zealand Prisoner Mental Health Study.

Key Results

Mental disorders

  • Nearly all (91%) prisoners had a lifetime diagnosis of a mental health or substance use disorder and 62% had this diagnosis in the past 12-months.
  • Female prisoners were significantly more likely to have a 12-month diagnosis of any mental disorder than male prisoners (75% compared to 61%).
  • General population comparison: Prisoners were three times more likely than the general population to have a 12-month diagnosis of any mental disorder (62% compared to 21%).

Anxiety disorders

  • Just over one in five (23%) prisoners had an anxiety disorder diagnosis in the past 12-months, while 30% had a lifetime anxiety diagnosis.
  • Female prisoners had a significantly higher prevalence of post-traumatic stress disorder compared to males for both 12-month and lifetime diagnoses, with over half (52%) of women having a lifetime post-traumatic stress disorder diagnosis.
  • General population comparison: A lifetime post-traumatic stress disorder diagnosis was four times higher among prisoners (24%) than in the general population (6%).
  • Prison population comparison: The lifetime prevalence of generalised anxiety disorder was just over 1% in the 1999 prisoner mental health study which had increased to nearly 9% in 2015, while the lifetime prevalence of panic disorder had also increased from nearly 2% in 1999 to nearly 6% in 2015.

Mood disorders

  • Nearly a third (32%) of prisoners had a lifetime diagnosis of any mood disorder, while 24% had a 12-month mood disorder diagnosis.
  • When compared to other ethnic groups, Māori prisoners had the lowest prevalence of lifetime diagnosis of major depressive disorder (17%).
  • General population comparison: The 12-month prevalence of any mood disorder was three times higher for prisoners (24%) than in the general population (8%).
  • Prison population comparison: When compared to the 1999 prisoner mental health study, the lifetime prevalence of major depressive disorder decreased slightly (from 23% to 21%), the lifetime prevalence of bipolar increased from 2% to 11%, and dysthymia increased from 1% to 5%.

Psychosis symptoms

  • The lifetime presence of psychosis symptoms (such as seeing visions and hearing voices) was present in 13% of prisoners, and in 7% of prisoners in the past year.
  • Prisoners with a lifetime diagnosis of an anxiety (23%) or mood (20%) disorder had the highest prevalence of ever experiencing symptoms of psychosis compared to 13% overall.
  • Prison population comparison: The lifetime prevalence of schizophrenia and related disorders was estimated to be 6% in the 1999 prisoner mental health study, while 12% of prisoners were found to report symptoms of psychosis in 2015.

Psychological distress

  • Over one in four (28%) of prisoners experienced psychological distress in the past 30 days.
  • There were significantly higher rates of psychological distress among female (47%) compared to male (27%) prisoners.
  • The prevalence of psychological distress was more than twice as high (60% compared to 28%) for prisoners with a 12-month diagnosis of an anxiety disorder compared to the total.
  • General population comparison: Prisoners were nearly five times more likely (28% compared to 6%) to have experienced psychological distress in the past 30 days compared to the general population from the 2013/14 New Zealand Health Survey.

Suicidal behaviours

  • Over one-third (35%) of prisoners had ever thought about suicide, 17% had ever made a suicide plan and 19% of prisoners had ever attempted suicide.
  • Female prisoners had higher rates of suicidal behaviours than men, including ever thinking about suicide (44% compared to 34%) and ever attempting suicide (29% compared to 18%).
  • General population comparison: Prisoners had higher rates of suicidal behaviours than people in the general population, including being twice as likely to have ever thought about suicide (35% compared to 16%) and four times as likely to have ever attempted suicide (19% compared to 5%).

Mental health treatment

  • Nearly half (46%) of prisoners diagnosed with a 12-month mental health or substance use disorder had received some form of mental health treatment in the past year.
  • Female prisoners had significantly higher rates of mental health treatment than males for nearly all disorders, including 60% of women with a 12-month diagnosis of any mental disorder obtaining mental health treatment compared to 45% of men.
  • Pacific peoples were substantially less likely to access health services for their mental health than prisoners of European descent (33% compared to 54%).
  • General population comparison: Fewer than half (46%) of prisoners with a 12-month diagnosis of any mental disorder received some form of mental health treatment in the past year, which was slightly higher (39%) than found in the general population.

In summary, prisoners had high rates of mental health and substance use disorders including high rates of comorbidity which were often undetected and under-treated. The findings of this report provide important evidence to assist with identifying areas for improved detection, early intervention, treatment and rehabilitation and diversion away from the criminal justice system. In particular, the findings suggest that improved integration of mental health and substance use disorder treatment would be an important strategy for improving the health and reducing re-offending among prisoners.

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