Mental health law and compulsory treatment

The Mental Health Act

The Mental Health Act 1983 is the law that allows people with a ‘mental disorder’ to be admitted, detained and treated in hospital without their consent – either for their own health or safety, or for the protection of other people.

This law is the most relevant to the treatment of people with psychosis in England and Wales. The Act was amended by the Mental Health Act 2007 and was slightly amended again by the Health and Social Care Act 2012. There is a separate page on this website about the Mental Health Act.

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The Mental Capacity Act

The Mental Capacity Act 2005 spells out different legal ways of making a wide range of decisions on behalf of someone aged over 16 when that person is unable to make a decision for themselves because they lack capacity.

The law defines ‘lacking capacity’ and how to determine whether someone is lacking capacity at any particular time.

An individual is considered to lack capacity to make a specific decision if they are: 

1) unable to understand information relevant to the decision; or
2) unable to retain that information; or
3) unable to weigh up and use the information to make the decision; or

4) unable to communicate their decision. 

An individual only has to meet one of these four criteria to be considered to lack the capacity to make a decision.

People experiencing mental illness may, because of the effects of the illness, sometimes lack capacity to make decisions about their treatment and care. However, case law stipulates that people who lack capacity because of their mental illness should be treated for that illness under the Mental Health Act. The Mental Health Act allows treatment to be given regardless of whether people have the capacity to consent.

The Mental Capacity Act may be used to give treatment for physical health problems to someone who lacks capacity because of their mental disorder – if someone who was experiencing psychosis needed hospital-based treatment for pneumonia, for example.

The Mental Capacity Act can be used to give treatment to somebody without their consent if that person is assessed as lacking capacity at that particular time, and if treatment would be in their 'best interests.' This means that any decision reached on behalf of the individual who lacks capacity must be the best course of action for him or her.

Mostly, the doctor who will be responsible for giving the medical treatment will be responsible for making the 'best interests' decision and in order to reach this decision, he or she must work through a process and statutory checklist which is contained in Section 4 of the Mental Capacity Act. This requires that they consider a range of factors when making the decision.

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Deprivation of liberty safeguards procedure

If hospital staff want to detain someone for treatment under the Mental Capacity Act, they may need to use the 'deprivation of liberty safeguards' procedure. This involves six assessments and aims to ensure that any decision to deprive someone who lacks capacity of their liberty is taken following a proper legal process. (The deprivation of liberty safeguard process should not be used to detain someone for treatment for their mental health problem: as stated above, the Mental Health Act should be used to detain someone for treatment for a 'mental disorder'.)

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Mental Capacity Act advance decisions

The Mental Capacity Act (sections 24, 25 and 26) specifically allows people to make an 'advance decision' to refuse treatment at a future time when they lack capacity (though this can be over-ruled in some instances). It also allows people to make a written statement about their wishes and preferences, should they lose capacity. These statements are not legally binding but should be considered when best interests decisions are being taken. The law also enables people to appoint 'an attorney' to make decisions for them if they lose capacity in future.

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Codes of Practice

There are Codes of Practice for the Mental Health Act, the Mental Capacity Act and the deprivation of liberty safeguards. These Codes of Practice give guidance about good practice and how to act within the law. Mental health professionals have to take account of them in their work.

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Independent mental capacity advocates and independent mental health advocates

Local authorities have a duty to arrange an independent mental capacity advocate (IMCA) service to provide help and support to people who are subject to the Mental Capacity Act 2005 (if they meet certain criteria). Local authorities also have a duty to arrange an independent mental health advocate (IMHA) service to provide help and support to people detained or treated under the 1983 Mental Health Act.



This page was updated 22 January 2013
Links last updated: 1 January 2015
Next links check due: April 2015


Mental Health Act Code of Practice

(a new Code of Practice will come into force on 1 April 2015. Visit GOV.UK for information about proposed changes)

Mental Capacity Act Code of Practice

Mental Capacity Act 2005 Deprivation of liberty safeguards – Code of Practice to supplement the main Mental Capacity Act 2005 Code of Practice

Best interests: Guidance on determining the best interests of adults who lack the capacity to make a decision (or decisions) for themselves (England and Wales)

A report published by the Professional Practice Board of the British Psychological Society and written by Theresa Joyce, a consultant clinical psychologist and Mental Capacity Act and safeguarding adults clinical 'lead' at South London and Maudsley NHS Foundation Trust.

Other useful websites

Mental Capacity Act - making decisions



Mental Health Act 1983

Mental Capacity Act 2005

Mental Health Act 2007
(amendments to the Mental Health Act 1983 and the Mental Capacity Act 2005)

Health and Social Care Act 2012