Mental capacity


  • What can cause a lack of mental capacity?
  • What happens if I lose mental capacity?
  • How can I plan ahead?

Someone may lack mental capacity if they can’t:

  • understand information about a particular decision
  • remember that information long enough to make the decision
  • weigh up the information to make the decision, or
  • communicate their decision

We all make big and small decisions every day of our lives. Most of us are able to make these decisions for ourselves. For some people, however, their capacity to make certain decisions about their life is affected. For example:

  • A person with a learning disability may lack the capacity to make major decisions such as where to live or how to invest their money, but can still make decisions about what to eat, wear and do each day
  • A person with mental health problems may be unable to make decisions when they are unwell but able to make them when they are well
  • A person with dementia is likely to lose the ability to make decisions as their dementia progresses

What can cause a lack of mental capacity?

Many things can cause a lack of mental capacity. It can be:

  • permanent, where someone’s ability to make decisions is always affected. This could be because of a stroke or brain injury, severe dementia or learning disability
  • temporary, where someone has capacity at some times but not others. This could be because of a mental health problem, substance or alcohol misuse, confusion, drowsiness or unconsciousness because of an illness or treatment

What happens if I lose mental capacity?

The Mental Capacity Act is designed to protect you if you don’t have mental capacity. It says:

  • you have the right to make your own decisions if you have the mental capacity
  • it is assumed you have mental capacity unless you’ve had an assessment showing you don’t. No one should say you lack capacity just because you make what seems to be an unwise or unusual decision
  • you must be helped to make your own decisions
  • any decisions made for you must be made in your best interests.

No one should decide you lack capacity or make assumptions about what’s in your best interests based on your age, appearance, mental health diagnosis or other medical condition.

The Mental Capacity Act applies to people in England and Wales. If you live in Scotland, there is a separate law: the Adults with Incapacity (Scotland) Act 2000.

The NHS website has more information about the Mental Capacity Act

How can I plan ahead?

Loss of mental capacity can happen unexpectedly, so it’s sensible to make plans in case you’re unable to make your own decisions. You can:

  • use a Lasting Power of Attorney (LPA) to appoint someone to make decisions on your behalf. This includes decisions about property and financial affairs as well as your health and personal welfare
  • make an advance decision to refuse treatment. This sets out the situations where you would want to refuse medical treatment if you lacked the capacity to make or communicate that in future. Advance decisions are legally binding. However, you can’t generally use one to refuse treatment you might be given if you’re detained under the Mental Health Act (‘sectioned’)
  • make an advance statement. This sets out your wishes, beliefs, feelings and values about your care and treatment in case you’re unable to communicate them in future. It isn’t legally binding but can help family, friends, and medical professionals make decisions on your behalf

* Last updated: 3 May 2021

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