While an advance care directive comes into force as soon as it is witnessed [Advance Care Directives Act 2013 (SA) s 16(1)], it may only be used by a substitute decision-maker or health practitioner if the person who gave the advance care directive has impaired decision-making capacity [s 34]. The impaired capacity must relate to the particular decision that has to be made at the time [s 34].

Impaired decision-making capacity

A person is considered to have impaired decision-making capacity in respect of a particular decision if any of the following apply [s 7]:

An advance care directive may set out when the person who made it is to be considered to have impaired decision-making capacity in relation to particular decisions [s 7(1)(b)].

Pursuant to s 10, a person is presumed to have full decision-making capacity, must be allowed to make their own decisions to the extent that they are able, and may make decisions in collaboration with others.

Decision-making capacity is not always static. A person may fluctuate between having impaired decision-making capacity and full decision-making capacity [s 7(2)(c)]. Further, a person's decision-making capacity will not be taken to be impaired merely because their decision results, or may result, in an adverse outcome for the person [s 7(2)(d)].