Pursuant to the Consent to Medical Treatment and Palliative Care Act 1995 (SA) a medical practitioner responsible for the care of a patient in the terminal phase of a terminal illness is under no duty to use or continue to use life sustaining measures if the effect would be merely to prolong life in a persistent vegetative state or moribund state without any real prospect of recovery [s 17(2)(a)]. This is the case even if the patient or the patient's representative requests the use or continuation of life sustaining measures. However, if the patient or their representative requests that life sustaining measures be withdrawn, the medical practitioner must withdraw them [s 17(2)(b)].

Section 17(1) further protects medical practitioners responsible for, or participating in, the care of a patient in the terminal phase of a terminal illness from civil and criminal liability where the administration of medical treatment with the intention of relieving pain or distress has the incidental effect of hastening the death of the person. This section applies provided that the medical treatment is provided:

In the circumstances above, a doctor who withholds medical support with or without the consent of the patient or their representative is not said to have caused death; the death is technically from 'natural causes'. The Criminal Law Consolidation Act 1935 (SA) does not relieve a medical practitioner from the consequences of a negligent decision as to whether or not the patient is suffering from a terminal illness.

Sometimes it is necessary for medical decisions to be made for a person who has impaired decision making capacity. This means another person or authority may need make a decision about the person's medical treatment, or the withdrawal of medical treatment, on their behalf (see When someone 16 or over can't consent).  

People often wish to have some say in what treatment they receive, or don’t want to receive, in these situations. A competent adult can make an advance care directive appointing a substitute decision maker and outlining their wishes in anticipation of losing decision making capacity (see Advance Care Directives).