In its simplest terms, mental capacity refers to the ability to make our own decisions.
All adults are presumed to have the capacity to make decisions about their own medical care.
Case law has determined that this presumption should specifically include the capacity to refuse treatment, even if that refusal might result in the death of the patient.¹

A patient will not simply 'have' or 'lack' capacity; it is time-specific and decision-specific. A patient's capacity might fluctuate, so they have capacity to make decisions about their treatment one day and not the next.

Similarly, a patient may have the capacity to make simple decisions about their care but lack the capacity to consent to more complex medical treatment.

The law

The law relating to mental capacity has changed over the last few years and now focuses on maximising a patient's potential capacity. The Assisted Decision-Making (Capacity) Act 2015 provides a new statutory framework for assisting patients who lack capacity to have as great an input as possible in their care and treatment.

The Act makes provisions for assisted decision-making in cases where a patient lacks capacity, and established the Decision Support Service, which started its core work in 2023 after preparing for the Act to come into force over the previous couple of years. This agency will provide codes of practice to assist doctors in understanding their obligations under the Act.

The Act formalises in law a four-stage test for the determination of mental capacity. It states that a patient will lack the capacity to make a decision if they are unable to:

understand all of the information relevant to the decision
retain the information for long enough to consider it
use or weigh up that information in their decision-making process
communicate their decision (by any means, including assistive technology, etc.)

Patients who have capacity might make decisions that appear unwise or even bizarre to a treating doctor, but the law is clear that any decision made by a competent patient must be respected, even if it appears irrational.²

The Act goes on to say that a patient should not be held to lack capacity simply because:

they need the information to be communicated to them in a particular way
they can only retain the information for a short time
they previously lacked the capacity to make the same decision
they lack the capacity to make other decisions.

In general terms, if a patient lacks capacity then the Act says a doctor must always treat that patient in accordance with their 'will and preferences'. This is a slight difference in emphasis to previous case law, which required doctors to act in the patient's best interests - although in practice these are likely to be closely aligned.

The Medical Council states in paragraph 14.6 of its guidance that doctors must still seek and listen to the views of patients who lack capacity. It goes on to say that doctors must consider the views of any decision-making supporter or person named by the patient as someone who should be consulted.

They should also take reasonable steps to find out whether anybody else has the legal right to make decisions on the patient's behalf and seek their consent for treatment.

When treating a patient who lacks capacity, the Medical Council requires doctors to consider:

which treatment would give the best benefit to the patient
the previously expressed wishes of the patient
the views of other people close to the patient
the views of other involved healthcare professionals
whether the patient is likely to regain their capacity to make the decision in the future.

They should also consult the Decision Support Service as necessary.

Where there is disagreement about what treatment would be in accordance with a patient's will and preferences that can't be addressed after consultation with the patient, those close to them or their decision-making supporter, it may be necessary to apply to a court to determine the legality of any proposed treatment.

If you're an MDU member and you need advice on this or any of the other points raised in this guide, you can contact us here.

Mental capacity in the Republic of Ireland

Related articles

Paying too much for your indemnity?