Please note: the Mental Health Act 2025 received Royal Assent on 18 December 2025. The Act will reform the Mental Health Act 1983, and implements reforms proposed by Sir Simon Wessely in his Independent Review of the Mental Health Act in 2018. The government has proposed a long-term implementation plan for the new Act, so people being detained under the Mental Health Act are not immediately affected. Exact timelines are not known, and it is likely to be at least several months before changes are implemented, with some changes potentially taking years. A new ‘Code of Practice’ is being developed which will set out more detailed guidance on the Act before it comes into force.

1. Introduction

Mental health and mental wellbeing mean different things to  different people. If a person feels well and has good mental health,  they will usually be able to cope with day to day life, make the most of their potential and take part in and enjoy social, family, community and work related activities.

When a person does not feel that they are in a state of good mental health, it can affect their life in many ways and daily life including work and socialising with family, friends, colleagues and the wider community can become difficult.

2. Mental Health Act 1983

In legal terms, the Mental Health Act 1983 does not use the term mental health, but refers instead to mental disorder.

2.1 Amendments to the Act

In 2007, the definition of mental disorder used in the Mental Health Act (MHA) 1983 was simplified, to ‘ any disorder or disability of the mind’.

This is a very wide definition and covers a range of disorders including schizophrenia, depression, anxiety disorders and eating disorders. However, suffering from one of these disorders by itself does not mean that a person is subject to the provisions of the MHA.

The Act also contains an exception for people with learning disabilities. A person will not fall within the definition of mental disorder simply because they have a learning disability. A learning disability only falls within the definition of a mental disorder if it is associated with abnormally aggressive or seriously irresponsible conduct.

A  person cannot be detained under the Act purely as a result of their learning disability alone.

The amendments made to the Act in 2007 also mean that people with personality disorders who were not previously able to be detained under the Act (because their disorders did not result in ‘abnormally aggressive or seriously irresponsible conduct on the part of the person concerned’) can now be detained.

There remains an exclusion that relates to a dependence on drink or drugs which means a person cannot be detained under the MHA 1983 solely for such a dependency, but they can be detained if it arises because of or from a mental disorder.

Chapter 2 of the Code of Practice to the Mental Health Act explains in further detail what illnesses may be considered under the Act and also references personality disorders and the MHA.

3. Further Reading

3.1 Relevant chapters

Section 117 Aftercare

Relationship between the Mental Capacity Act 2005 and the Mental Health Act 1983

3.2 Relevant information

Mental Health Act 1983: Code of Practice

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