Mental capacity

The Mental Capacity Act in England and Wales, and Adults with Incapacity Act in Scotland, aim to protect people who cannot make a decision for themselves.

What is mental capacity?

Mental capacity means being able to make decisions for yourself.

In England and Wales, the Mental Capacity Act 2005 aims to protect people who cannot make a decision for themselves (do not have capacity).

In Scotland, the Adults with Incapacity Act 2000 (Scotland) protects people who do not have capacity.

These acts allow other trusted people to make decisions for you, in your best interests. This might include decisions about your medical treatment or managing your finances and property. This means it can help you plan ahead and also protects you if you have not planned ahead.

A person lacks capacity if they cannot:

  • understand information about the decision
  • use or consider the information to act on the decision
  • remember the information and making decisions
  • communicate their decision by talking, using sign language or any other means.

Different conditions of the brain and nervous system might affect a person’s mental capacity or ability to communicate. This can include dementia, brain injuries, some mental health conditions or being unconscious.

Having one of these conditions does not always mean that you do not have the mental capacity to make certain decisions. Your ability to make decisions can change as your health changes.

If a person does not have mental capacity these acts explain:

  • who can make decisions for them
  • in which situations they can make decisions
  • the process to follow when making decisions.

If it is not clear whether someone has mental capacity, doctors do a number of tests. They may also get advice from a specialist. This may take a while because it is important to understand how mental capacity changes over time. If the decision is not urgent and you do not have capacity, it may be delayed. This is to see if your condition improves enough for you to be involved in decision-making.

Healthcare professionals will support you and those around you to make decisions about your care and wishes. Even if you do not have capacity to make decisions, your healthcare team try to understand your wishes and involve you as much as possible.

Related pages

Managing your care if you have not planned ahead

If you have not planned ahead for any future care and cannot communicate or make a decision for yourself, you are protected by the Mental Capacity Act (England and Wales) and the Adults with Incapacity Act (Scotland).

Usually, you, your family, carers or close friends will be involved in making everyday decisions about your care. But sometimes, an important or difficult decision may need to be made about your medical care or treatment in an emergency.

If you are not able to make and communicate your own decisions, a senior healthcare professional usually decides about your care in an emergency situation.

Decisions about your care must be made in your best interests.

England and Wales

In England and Wales decisions are guided by the Mental Capacity Act.

Sometimes a senior health professional will need to make a decision about your medical care and treatment. They must do their best to make sure any treatment will be of most benefit to you. They will base their decision on what they know about:

  • your situation
  • your wishes
  • any advance statements you may have made
  • their experience.

They will discuss the decision with your family, friends and anyone else involved in your care. This is to make sure any care or treatment will provide the most benefit to you. But a senior health care professional will have the final responsibility for the decision. These decisions are called best interests decisions.

Sometimes this means that what the family might want is not able to happen. In this situation, the healthcare professional should explain the reasons for their decision and the law regarding best interests decisions.

Making a best interests decision

If a best interests decision is about life-sustaining treatment, a health professional looks at the treatment options to make sure that the best interests of a person are met.

The Mental Capacity Act gives healthcare professionals a list of things to think about when making a best interests decision. These include:

  • all the relevant circumstances
  • your past and present wishes
  • your values and beliefs
  • the views of people caring for you, such as family members, friends or carers.

The Mental Capacity Act also states that a best interests decision must not be based on your age, condition, appearance or any aspect of your behaviour.

The Act also ensures that those who make decisions think about all the relevant circumstances about your care. It also makes sure that the motives of the person making the decision are correct and in your best interests.

Independent mental capacity advocates

In some situations, medical staff may need to appoint an independent mental capacity advocate (IMCA). This person acts as your advocate and represents your interests and views, if you cannot do so yourself. You can find out more about the IMCA service at They provide a booklet called Making decisions –The Independent Mental Capacity Advocate (IMCA) service.


The Adults with Incapacity (Scotland) Act 2000 gives healthcare professionals a list of things to think about when making their decision. They must do their best to make sure any treatment will be of most benefit to you. They need to think about:

  • your wishes, if your healthcare professionals know them or can find them out
  • what the people who know you well think you would prefer.

In a non-emergency situation, they still have to think about the same things. But first a doctor checks whether you have the mental capacity to make a decision for yourself. If you are unable to make the decision, the doctor completes a certificate to record this.

They then make the treatment decision for you. If possible, they will talk to people close to you about what your wishes are likely to be.

You can read more about the Adults with Incapacity Act 2000 (Scotland).

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    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Viv Lucas, Consultant in Palliative Medicine.

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Date reviewed

Reviewed: 01 June 2023
Next review: 01 June 2026
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