Mental capacity and the law

This information is for anyone who wants to know more about capacity, and how the law protects you when you cannot make decisions yourself.

It is based on the 2005 Mental Capacity Act for England and Wales. Scotland has a similar Act called the Adults with Incapacity Act (2008).


This leaflet provides information, not advice.

The content in this leaflet is provided for general information only. It is not intended to, and does not, mount to advice which you should rely on. It is not in any way an alternative to specific advice.

You must therefore obtain the relevant professional or specialist advice before taking, or refraining from, any action based on the information in this leaflet.

If you have questions about any medical matter, you should consult your doctor or other professional healthcare provider without delay.

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Every day we make decisions about our health. We decide whether to smoke or not, whether to exercise or not – and what treatments we are prepared to have.

We have the legal right to make a decision because it seems to be for us; it's “in our own best interest”.

What is capacity?

You have capacity when you decide for yourself  - without someone else having to decide for you.


If a physical or mental illness affects your thinking so that:

  • you can't  make a decision for yourself

  • you would make a decision that you would not make if you were well.

The law say that you "lack capacity" to make that decision.


With the decision to be made

Even if your thinking is affected, you may still be able to make simple decisions, but not more complicated ones. 

Say you have dementia, and can't remember new information.

You may be able to decide about a place you'd like to visit, but may not be able to decide whether to have a hip operation or not.

When you have to make the decision

Capacity can change with time because your state of mind can change with time. An illness that interferes with your thinking can get better – at least for a while. 

An older person can become confused with a chest infection, so that they can't make many decisions properly. 

Their normal state of mind can return when the infection is treated and they can, again, make decisions in the way they normally would.

Normally you decide about whether you want a treatment. You decide what’s best for you.

You can disagree with your doctor, even if the doctor finds it hard to understand. For example, a Jehovah’s Witness may refuse a blood transfusion because it is against their religion. If you have capacity, the doctor has to accept your decision.

It is harder when you need to make a decision, but you don't have the capacity to make it. An infection, a mental illness or dementia may interfere with your thinking. The Mental Capacity Act helps us to work out what to do in these situations.

This Act protects people lacking capacity from having decisions made for them that are not in their best interests. This can happen when:

  1. Someone makes the decision, but does not know the person well. For example, a doctor might start a treatment that you would normally refuse.

  2. A person exploits the patient with impaired capacity. You might give someone money to spend for you, but they then keep it for themselves.

There are 5 principles:

  • You have capacity, unless the tests described below show that you don't. 

  • Your best interests come first. Any decision must be as close as possible to what you would have normally wanted for him yourself.

  • You can have help to make a decision for yourself. A decision can be put off or family members can support you while you think about it.

  • If you have the capacity to make a particular decision, you have the right to make a decision that others might see as unwise.

  • If the decision has to be made for someone else, it should be the least disturbing and least dangerous option for them - the "least restrictive action".

There are four questions which need to be answered.

1) Do you understand the information?

To decide about a treatment, you need to understand what you might gain from it, what the risks are, any other treatments available and what might happen if you don't have any treatment.

2) Can you retain this information?

If you can understand the relevant information, but can't remember it for more than a few seconds or minutes, you won't be able to use it to make an informed decision.

3) Can you weigh up the information?

Can you compare the benefits and risks and use this to make your decision? You may be able to understand the information (test 1), remember it (test 2), but not be able to weigh facts as you would normally.

If you have a psychosis, you may be influenced or distracted by the voices that your are hearing. If you are very depressed, you may feel so hopeless that any treatment seems pointless, even though there is a good chance of recovery.

4) Can you communicate your decision?

You can do this by talking, writing, in sign language, by nodding or even blinking an eyelid.

The answer must be yes to all four of the above questions for you to have capacity.

Any professional can test capacity. This should be the person most directly involved with the issue at hand.

For health decisions, this should be the doctor. If a lawyer is drawing up a will, but has doubts  about their client's capacity, they may ask for an expert opinion from a psychiatrist or a psychologist.

  • A doctor who wants to treat you under the MCA must contact your family (or close friends/care workers if there is no family) to find out what you would normally want.
  • The Court of Protection oversees everything to do with capacity.
  • You can give someone the power to make decisions for you if you lose capacity in the future. This is called Lasting Power of Attorney (LPA). You have to do this when you still have capacity.
  • You can make an “Advanced Decision” This is a way of planning ahead, while you still have capacity. You can say that you want (or don't want) certain treatments if you lose capacity in the future. You can use this if you have a disorder that just worse, like dementia.
  • If you have no family or close friends to speak for you, an Independent Mental Capacity Advocate (IMCA) can help you.

If you don't have the capacity to decide about treatment, the Mental Capacity Act gives doctors and nurses the power to give you a physical treatment against your will. 

If it  has to be done, it can be upsetting, so this step is taken seriously.

For mental illnesses, the Mental Health Act is used instead.

This allows a psychiatrist to treat you against your will, even if you still to have capacity, but they seem to be a risk to yourself or other people's safety, or so ill that you need the treatment.

If you:

  • are worried about your capacity;
  • are worried about the capacity of a friend or relative;
  • feel you are being pressurized into a treatment you don’t really want

discuss this with your doctor or any member of the team.

If you still aren't happy, you can contact the following organisations.

Alzheimer's Society

UK care and research charity for people with this disease and other dementias, their families and carers.


National charity to support people with learning disability.

MIND: Infoline: 0300 123 3393.

Mental health charity with information on capacity issues.

  • Authors: Dr Sohom Das and Dr Michael Yousif
  • Series Editor: Dr Philip Timms
  • User and Carer input: members of the RCPsych Service User Recovery Forum and Carers Forum.

Published: May 2018

Review due: May 2021

© Royal College of Psychiatrists