Mass. Gen. Laws ch. 201D § 6
The authority of a health care agent shall begin after a determination is made, pursuant to the provisions of this section, that the principal lacks the capacity to make or to communicate health care decisions. Such determination shall be made by the attending physician according to accepted standards of medical judgment. The determination shall be in writing and shall contain the attending physician's opinion regarding the cause and nature of the principal's incapacity as well as its extent and probable duration. This written determination shall be entered into the principal's permanent medical record.
If the attending physician determines that a patient lacks capacity because of mental illness or developmental disability, the attending physician who makes the determination must have, or must consult with a health care professional who has, specialized training or experience in diagnosing or treating mental illness or developmental disabilities of the same or similar nature in making such determination.
A physician who has been appointed as a patient's agent shall not make the determination of the patient's capacity to make health care decisions.
Notice of a determination that a principal lacks capacity to make health care decisions shall promptly be given orally and in writing: (i) to the principal, where there is any indication of the principal's ability to comprehend such notice; (ii) to the agent; and (iii) if the patient is in or is transferred from a mental health facility, to the facility director.
A determination made pursuant to this section that a principal lacks capacity to make health care decisions is solely for the purpose of empowering an agent to make health care decisions pursuant to a health care proxy.
Notwithstanding a determination pursuant to this section that the principal lacks capacity to make health care decisions, where a principal objects to a health care decision made by an agent pursuant to a health care proxy the principal's decisions shall prevail unless the principal is determined to lack capacity to make health care decisions by court order.
In the event the attending physician determines that the principal has regained capacity:
Mass. Gen. Laws ch. 201D, § 6