Mental capacity is the ability to make a decision for yourself.
While you have mental capacity you have the right to make decisions about your medical treatment and care. You can choose to refuse or consent to treatment. If you have made a living will (advance decision) it will only be used if you do not have mental capacity to make or communicate a decision for yourself.
The law in England and Wales says that someones mental capacity should be assumed, unless there is reason to question it. For example, if they have had a brain injury or a diagnosis of dementia.
You must be able to do all four of these things to have mental capacity to make a decision:
- Understand the information
- Retain the information long enough to make a decision
- Weigh up the information against other factors
- Communicate the decision once you have made it
Mental capacity is decision specific. This means that someone may have the mental capacity to make some decisions but not others. For example, someone with advanced dementia may have the mental capacity to decide what they want to eat that day, but not to make a decision about refusing CPR.
In Scotland and Northern Ireland the principle of mental capacity is similar, but they have their own definitions. The Office of the Public Guardian in Scotland has a helpful definition of incapacity on their website. The Department of Health NI define mental capacity in their Code of Practice (PDF, 2.8MB).