Health professionals must have consent from a person (or someone authorised to give consent on their behalf) prior to undertaking invasive medical procedures, except in an emergency situation if treatment is necessary to prevent a serious and imminent threat to the patient’s life or health.

A person who has capacity is able to consent to, or refuse, treatment or other medical procedures.

Capacity is defined as the ability to understand the nature and effect of a proposed decision and communicate consent or refusal with respect to that decision.

A person may lose or have reduced capacity either temporarily or permanently due to a number of reasons, such as a disability, mental illness, disease or trauma from an accident.



A person is presumed to have capacity until proven otherwise. Capacity is a legal construct.

Legally, a person with capacity must:

  • understand information material to the decision, including the nature and the effect of the decision;
  • be able to evaluate and weigh-up the consequences of the different decisions; and
  • be able to communicate the decision in some way (by speaking, writing or some other means, such as sign or body language).

Some people may make decisions that a health professional may disagree with or that they think is irrational. However, this does not necessarily mean that that person lacks capacity.

Incapacity is not:

  • Ignorance.
  • Eccentricity, cultural diversity or having different religious or ethical views.
  • ‘Bad’ or seemingly irrational decisions.
  • Disagreeing with a doctor or other health staff.


Specific Capacity

Previously capacity was considered to be ‘black or white’ — a person either had capacity or they didn’t. However, now capacity is not considered to be absolute, and there is recognition of the concept of ‘specific capacity’. Capacity can fluctuate, and a person who was deemed to not have capacity can regain capacity at a later date. A person may also have capacity to make some decisions at certain instances, but not at others. For example, a person may have capacity to make financial decisions but not medical decisions at a particular time.

Capacity can therefore be domain specific, decision specific and time specific. Different degrees of capacity can be required for different decisions. The important question to ask is: ‘Does this person have capacity to make this type of decision at this particular time?’


Substitute Decision-Making

If a person is deemed to not have capacity, there may be a substitute decision-maker who is authorised to make the medical or dental treatment decision on their behalf.


There are a number of formal legal options for substituted decision-making. Please click on the links below for more information: