Decision-making and mental capacity

Mental capacity is the ability to make decisions for yourself. People who cannot do this are said to 'lack capacity'. This might be due to injury, a learning disability, mental health problem or a condition such as dementia.

To have capacity a person must be able to:

  • understand the information that is relevant to the decision they want to make
  • retain the information long enough to be able to make the decision
  • weigh up the information available to make the decision
  • communicate their decision by any possible means, including talking, using sign language, or through simple muscle movements such as blinking an eye or squeezing a hand.

It is important to be aware that the mental capacity of a person with dementia can change over time, both in the short and long term. As an example, there might be days or even times of the day when they are able to think more clearly than others, so a person may have capacity at some times and lack it at others.

A person may also have the capacity to make some decisions and not others, as some decisions require the person to understand more complex information, or weigh up more options, than others. You should not assume a person lacks capacity to choose what to wear or eat just because they cannot make difficult financial or medical decisions.

The Mental Capacity Act and dementia

If you are making a decision for someone who lacks capacity then you must ensure that it is made in their best interests. Find further information and advice in this section.

Read more

The principles of the Mental Capacity Act

The Mental Capacity Act (MCA) is based on five key principles. These are mentioned throughout this section, but are listed below for reference:

  1. Every adult has the right to make decisions for themselves. It must be assumed that they are able to make their own decisions, unless it has been shown otherwise.
  2. Every adult has the right to be supported to make their own decisions. All reasonable help and support should be given to assist a person to make their own decisions and communicate those decisions, before it can be assumed that they have lost capacity.
  3. Every adult has the right to make decisions that may appear to be unwise or strange to others.
  4. If a person lacks capacity, any decisions taken on their behalf must be in their best interests. (The act provides a checklist that all decision makers must work through when deciding what is in the best interests of the person who lacks capacity - see below.)
  5. If a person lacks capacity, any decisions taken on their behalf must be the option least restrictive to their rights and freedoms.
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