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The Royal College of Psychiatrists Improving the lives of people with mental illness


Mental Illness, Offending and Substance Misuse


About this leaflet

This leaflet is for members of the public who want to know more about mental illness, offending and substance misuse.  


Mental illness, offending and substance misuse

We describe what is meant by mental disorder, offending and substance misuse and how often they are seen together.  Also we will talk about treatments and other sources of help. We examine whether people with mental illness are more likely to commit violent crimes.


Offending and mental health

Mental illness is sometimes called a ‘mental disorder’. This includes schizophrenia, bipolar disorder, drug-induced psychosis, personality disorder, depression, anxiety and post-traumatic stress disorder. These are just some examples of mental disorders.


The branch of psychiatry dealing with the assessment and treatment of offenders with mental health problems is called ‘forensic psychiatry’.


How common are mental health problems in prison?

Studies have found that mental health problems are much more common in prisoners than in the general population.  As much as 9 out of 10 prisoners report some kind of mental health problem and the most commonly reported symptoms in prisoners are sleep problems and worrying.


What types of crimes are committed by people with mental illness?

The types of crime committed by people with mental illness are no different from the crimes committed by people who do not have mental illness.


What happens to mentally disordered offenders?

Mentally disordered offenders still go through the criminal justice process as anyone else would. However, there are measures in place to help people with mental illness. There are assessments to identify people who would be best helped in hospital. The Courts can also ask for a psychiatric report to help them decide on the best course of action. 


Sometimes offenders with a severe mental illness are sent to hospital rather than prison to serve their sentence. This decision depends on how severe their mental illness is.  People with less severe mental health problems can get help in prison from mental health ‘In reach’ teams. 


What treatment is available?

This may include medicines or psychological treatments to reduce criminal behaviour and to help people understand their mental illness.

The programmes currently running in prisons include:

  • Reasoning and Rehabilitation
  • Anger Management
  • Cognitive Self Change
  • Sex Offender Treatment.

Substance misuse and mental illness

Substance misuse is the taking of a drug or alcohol in such a way that it leads to harm. Examples of harm include: addiction, debt, physical harm, criminal actions and relationship problems.

The drugs used may be:

  • Legal substances (e.g. alcohol)
  • Illegal substances, such as opiates (e.g. heroin), stimulants (e.g. cocaine, crack, amphetamines and ecstasy) and cannabis
  • Prescription drugs used in a way not intended by the doctor (e.g. benzodiazepines).

If someone has a mental illness along with a substance misuse problem, they are said to have a ‘dual diagnosis’.


Is there a link between mental illness and substance misuse?

Research shows that substance misuse may cause or increase symptoms of mental illness. On the other hand, mental illness may lead someone to abuse substances. They may want to block out their symptoms or the side-effects of medication. They may have difficulties in sleeping, feel lonely or simply wish to boost their self-confidence.


People with a dual diagnosis have other problems including being lonely, homeless, having a history of abuse and are more likely to get into trouble with the police.


Depression, anxiety and schizophrenia are more likely to be linked to substance misuse. The drug use can stop people making a full recovery. It is also more likely to lead to becoming unwell again or to have to be re-admitted to hospital.


How common are these problems?

The UK has one of the highest levels of drug misuse in Europe.


About a quarter of people in the UK drink more alcohol than they should. The amounts drunk have doubled over the last 50 years and are still rising. Physical health problems caused by alcohol have doubled in the last 10 years. Deaths have doubled over the last 15 years.


About 35% of people aged 16-59 have used illegal drugs in their lifetime. Cannabis is the most commonly used drug.


Dual Diagnosis - substance misuse problems are common among people in mental health services. The number of people with a mental illness and who misuse substances has increased by 62%, in particular for those suffering from schizophrenia.


What are the consequences?

People with dual diagnosis do worse than those with mental health problems alone. They are also more likely to be admitted to hospital, to self-harm and commit suicide.

The combination of having a mental illness, substance misuse and not taking medication can increase the risk of violence toward others. However this makes up only a small amount of violent acts.


Drug-related violent crime

This can be split into:

  • violence from effects of the drug
  • violence from interaction between a mental illness and drug use
  • violence related to stealing to get money from drugs
  • fighting between drug users, dealers or gangs.           

Prisons, mental health and drugs

Unfortunately, dual diagnosis is often seen in people in prison. The criminal justice system tries to help people with drug problems through prison-based drug treatments and community punishments which include drug rehabilitation programmes.


Other sources of help

Alcoholics Anonymous Phone: 0845 769 7555

Centre for Mental Health

They have objectives to improve the lives, mental health and wellbeing of offenders and enhance the lives of people with mental health problems through employment.

Mental Health Foundation

Provides information and support for everyone with mental health problems or learning disabilities.


Promotes the views and needs of people with mental health problems. Phone: 0845 766 0163.


Narcotics Anonymous Phone: 0300 999 1212.


Nacro Crime reduction charity who work with disadvantaged people, offenders and those at risk of offending


Resettlement Plus Helpline

Nacro's helpline offers specialist support and advice to prisoners, ex-offenders and their families on 020 7840 6464.


Mental Health Primary Care in Prison

A guide to mental ill health in adults and adolescents in prisons and young offender institutions.



1.    Peay, J 2007.  Mentally disordered offenders, mental health and crime, in MacGuire M. et al. (eds) the Oxford Handbook of Criminology, 4th ed. Oxford: Oxford University Press

2.    Advisory Council on the Misuse of Drugs (2006) Pathways to Problems: Hazardous use of tobacco, alcohol and other drugs by young people in the UK and its implications.

3.    NHS Information Centre (2008) Statistics on Alcohol: England 2008, London, NHS Information Centre.

4.    Frisher, M., Crome I., Macleod, J., Millson, D., and Croft, P. (2005) Substance abuse and psychiatric illness: Prospective observational study using the General Practice Research Database. Journal of Epidemiology and Community Health, 59, pp.847–850.

5.    Swanson, J., Borum, R., Swartz, M., and Hiday, V. (1999) Violent behaviour preceding hospitalisation among persons with severe mental illness, Law and Human Behaviour 23, pp.185–203.

Expert Review: Dr Ali Ajaz and  Dr Paula Murphy
Series Editor: Dr Philip Timms, chair, Royal College of Psychiatrists' Public Education Editorial Board
This leaflet reflects the best available evidence available at the time of writing.

 Royal College of Psychiatrists. This leaflet may be downloaded, printed out, photocopied and distributed free of charge as long as the Royal College of Psychiatrists is properly credited and no profit gained from its use. Permission to reproduce it in any other way must be obtained from the Head of Publications. The College does not allow reposting of its leaflets on other sites, but allows them to be linked directly.

For a catalogue of public education materials or copies of our leaflets contact: Leaflets Department, The Royal College of Psychiatrists, 21 Prescot Street, London E1 8BB, Telephone: 020 7235 2351x 2552
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