Intended for healthcare professionals

Clinical Review

Assessing mental capacity: the Mental Capacity Act

BMJ 2008; 336 doi: (Published 07 February 2008) Cite this as: BMJ 2008;336:322
  1. Timothy R J Nicholson, specialist registrar in psychiatry 1,
  2. William Cutter, consultant psychiatrist 2,
  3. Matthew Hotopf, professor of general hospital psychiatry1
  1. 1Department of Psychological Medicine, Institute of Psychiatry, Western Education Centre, London SE5 9RJ
  2. 2Directorate of Older Persons’ Mental Health Services, Hampshire Partnership NHS Trust, Southampton, Hampshire SO40 2RZ
  1. Correspondence to: M Hotopf m.hotopf{at}
  • Accepted 28 November 2007

Assessing mental capacity is an important part of a clinician’s role, and the recent Mental Capacity Act can help doctors when making such decisions

Summary points

  • The Mental Capacity Act has resulted in increased formalisation of capacity law and assessment

  • The act has increased the expectation that healthcare workers should be competent at assessing capacity

  • The act has also increased the need for training and education, especially awareness and understanding of the code of practice, independent mental capacity advocates, and advance decisions

Clinicians are often confronted with decisions about mental capacity. Healthcare workers in England and Wales should therefore be aware of the recent changes to how capacity is assessed and the way that adults lacking capacity are dealt with since the implementation in 2007 of the Mental Capacity Act 2005.1

What does the Mental Capacity Act do?

The act protects people who lack the mental capacity to make decisions. Until the Mental Capacity Act 2005 was implemented no statutory law covered this area. Courts previously dealt with capacity under “common law,” which consists of the accumulated judgments of individual cases. The Mental Capacity Act is underpinned by five key principles (box 1), which are illustrated in a hypothetical scenario (box 2).

Box 1: Five key principles of the Mental Capacity Act

  • Principle 1: Capacity should always be assumed. A patient’s diagnosis, behaviour, or appearance should not lead you to presume capacity is absent

  • Principle 2: A person’s ability to make decisions must be optimised before concluding that capacity is absent. All practicable steps must be taken, such as giving sufficient time for assessments; repeating assessments if capacity is fluctuating; and, if relevant, using interpreters, sign language, or pictures

  • Principle 3: Patients are entitled to make unwise decisions. It is not the decision but the process by which it is reached that determines if capacity is absent

  • Principle 4: Decisions (and actions) made for people lacking capacity must …

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