Assessment of capacity in a medical and psychiatric setting is a key skill of a foundation year doctor and a common OSCE station in final year clinical examinations. Making decisions when patients lack capacity is governed by the Mental Capacity Act 2005 in England and Wales and the Adults with Incapacity Act 2000 in Scotland. Most of this guidance pertains to the legislation in Scotland, however, the two are broadly similar.

NB: There is at present no primary legislation on capacity covering Northern Ireland.(1)


Capacity should be judged in relation to individual issues/situations and not as an all or nothing approach.(2) Every possible effort should be made to maximise a patient’s capacity to make an autonomous decision about their care. A patient is deemed to lack capacity if they are incapable of:

  • Acting on (ie following through)
  • Making
  • Communicating
  • Understanding or
  • Retaining memory of their decisions.(1)


Components to Capacity

Mental Capacity Act 2005

Five principles must be applied to any action or decision taken under the terms of the Act:


  1. Capacity must always be assumed unless it has been established that the patient lacks capacity

  2. A patient must not be treated as unable to make a decision until all practical steps to help him/her do so have been taken without success

  3. A patient must not be treated as unable to make a decision simply because he/she makes an unwise decision

  4. A decision or action made under the Act must be in the patient’s best interests

  5. Decisions made must be the least restrictive option in terms of the patient’s rights and freedom of action.(1, 3)

Key Questions in assessing capacity:

Adults with Incapacity (Scotland) Act 2000

The act safeguards the welfare of persons aged 16 or over who lack the capacity to take some or all decisions for themselves due to either:

  • A mental disorder (eg schizophrenia) or
  • An inability to communicate their decision because of a physical disorder.

It allows other people to make decisions on the patient’s behalf and defines the principles which must be adhered to when deciding to intervene.

Any intervention must be:

  • Necessary & must benefit the patient
  • The minimum necessary to achieve the desired outcome.


Those making decisions on the patient’s behalf must:

  1. Take account of the patient’s present & past wishes and have exhausted every possible means of communicating with the patient to ascertain these
  2. Take account of the views of the patient’s nearest relative & primary caregiver & of any other person with the powers to intervene or with an interest in the person as far as is reasonable & practical to do so
  3. Encourage the patient to use any skills which they have to make decisions
  4. Consider if it’s possible to intervene without employing the Act.(1)


Relatives with power of attorney can make decisions on the patient’s behalf as long as they comply with the principles outlined above, they cannot, however, veto or indeed demands specific treatments.(4)



  1. The General Medical Council. Consent: patients and doctors making decisions together June 2008. Available from: (accessed 9th April 2012).
  2. Cogan A, Rasul N. Assessing Capacity. Presented at Year 4 Undergraduate Psychiatry Centralised Teaching, University of Glasgow. Glasgow, 2012.
  3. Department of Health. Mental Capacity Act. London: Stationery Office, 2005. Available from: (accessed 9th April 2012).
  4. The Scottish Executive. The Adults with Incapacity Act 2000. London: HMSO, 2000, Available at: (accessed 9th April 2012).

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