Assessing mental capacity

Within the context of the Mental Capacity Act 2005, mental capacity means the ability to make a decision. A person’s capacity to make a decision can be affected by a range of factors such as a stroke, dementia, a learning disability or a mental illness.

People with a mental illness do not necessarily lack capacity. However, people with a severe mental illness may experience a temporary loss of capacity to make decisions about their care and treatment.

A person’s capacity may vary over time or according to the type of decision to be made. Physical conditions, such as an intimidating or unfamiliar environment, can also affect capacity, as can trauma, loss and health problems.

A temporary lack of capacity will also include those who are unconscious or barely conscious whether due to an accident, being under anaesthetic or as a result of other conditions or circumstances such as being under the influence of alcohol or drugs.

The Mental Capacity Act 2005 was implemented in 2007. It is different from the Mental Health Act 1983. In the past, it was not unusual for some people, for example people with severe or enduring mental health problems, to have decisions made for them. This resulted in numerous injustices, such as mass institutionalisation, forcible treatment, loss of control of their own finances and loss of the right to vote.

The Mental Capacity Act applies to all people making decisions for, or acting in connection with, those who may lack capacity to make particular decisions. The staff who are legally required to have regard to the code of practice when acting in relation to a person who lacks, or who may lack, capacity are as follows:

Anyone who is a deputy appointed by the Court of Protection.

People who are being paid to provide care or support, such as care assistants, home care workers, support workers, staff working in supported housing, prison officers and paramedics.

Anyone acting as an independent mental capacity advocate (IMCA).

People working in a professional capacity such as doctors, nurses, social workers, dentists, psychologists and psychotherapists.

Anyone carrying out research involving people who cannot make a decision about taking part.

What triggers an assessment?

The Mental Capacity Act states that a practitioner should always start from an assumption of capacity. Doubts as to a person’s capacity to make a particular decision can occur because of:

The way a person behaves.

Their circumstances.

Concerns raised by someone else.

Other important triggers could be the death or move of a person who has been providing care, or a referral to an adult protection co-ordinator. Any doubts must be considered in relation to the specific decision to be made. Practitioners should also remember that an unwise decision does not necessarily indicate lack of capacity.

There are two questions to be asked if you are assessing a person’s capacity:

Is there an impairment of, or disturbance in, the functioning of the person’s mind or brain?

If so, is the impairment or disturbance sufficient to cause the person to be unable to make that particular decision?

This two-stage test must be used, and a practitioner must be able to show that it has been. Remember that most people will be able to make most decisions, even when they have a label or diagnosis that may seem to imply that they cannot. This is a general principle that cannot be over-emphasised.

The assessment process has to be clear and accountable. It will require input from staff in the range of organisations involved in providing support, and should include family and carers. Where there is no family or carer or other person authorised to make decisions for that person, an IMCA may be assigned if there is an important decision about certain medical treatment or a change of accommodation to be made. Other advocates may also be able to offer support, representation or advice, and staff need to be familiar with the local services and know how to contact them.

All professional staff involved in an assessment should keep adequate records that explain the grounds on which a person is found to have, or lack, capacity. Any assessment of a person’s capacity must consider the following factors:

Whether they are able to understand the information.

Whether they are able to retain the information related to the decision to be made.

Whether they are able to use or weigh that information as part of the process of making the decision.

The person has to be able to do all three to make a decision and they have to be able to communicate that decision. This could include alternative forms of communication such as sign language or blinking an eye or squeezing a hand when verbal communication is not possible. Other factors to be included in an assessment of capacity include:

General intellectual ability.


Attention and concentration.


Information processing – how a person interprets what they are told.

Verbal comprehension and all forms of communication.

Cultural influences.

Social context.

Ability to communicate.

Further information:

Mental Capacity Act training materials

Department of Health 

Department for Constitutional Affairs 



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