Who Decides Your Medical Treatment in Ontario If You Have No Power of Attorney?

Picture this: a 58-year-old is rushed to the hospital after a serious stroke. She is unconscious and cannot communicate. Her adult children are in the waiting room. A doctor needs consent to begin a particular course of treatment — but there is no power of attorney for personal care. Who actually has the legal authority to say yes or no?

This is not an unusual situation, and the answer is not simply "the next of kin." Ontario has a detailed substitute decision maker hierarchy set out in the Health Care Consent Act that determines, step by step, who speaks for you when you cannot speak for yourself. Understanding how that hierarchy works — and why it can go wrong — is one of the strongest arguments for putting a power of attorney in place before you ever need one.

How the Hierarchy Works Under the Health Care Consent Act

When a patient is incapable of consenting to a treatment decision, the Health Care Consent Act directs the health care provider to turn to a substitute decision maker (SDM). The Act establishes a ranked list. Working from the top down, the first person who is available, willing, capable, and not prohibited by a court order becomes the SDM. If no one on the list qualifies, the matter falls to the Public Guardian and Trustee — a government office — as the last resort.

The ranked order is:

1. Guardian of the person (if one has been appointed by a court under the Substitute Decisions Act)
2. Attorney for personal care named in a valid power of attorney document
3. Representative appointed by the Consent and Capacity Board
4. Spouse or partner (including a conjugal partner of at least one year, or a partner of any duration if they have a child together)
5. Child aged 16 or older, or a parent of the patient
6. Parent who has only a right of access (not full custody)
7. Sibling
8. Any other relative by blood, marriage, or adoption
9. The Public Guardian and Trustee

The person at the highest applicable rank takes priority. "Available" means genuinely reachable and able to engage in a timely way — not simply reachable in theory. "Willing" means they agree to act. "Capable" means they themselves have the mental capacity to make the decision and are at least 16 years old.

What an SDM Can and Cannot Do

The SDM's authority is real but it comes with important limits. Ontario law imposes two distinct standards, depending on what is known about the patient's wishes.

If the patient expressed capable wishes — whether in a written document, a conversation, or any other way — the SDM must follow those wishes, even if the SDM personally disagrees. This is not optional. A parent who told her doctor she never wanted to be kept alive by a ventilator expressed a capable wish. Her SDM is bound to honour it.

If no capable wishes are known, the SDM must act in the patient's best interests. The Health Care Consent Act sets out factors to consider: the patient's values and beliefs, their wellbeing, the likelihood that treatment will improve or maintain their condition, and whether withholding treatment is consistent with their life circumstances. It is a genuine judgment call, and reasonable people can disagree.

What the SDM cannot do is substitute their own preferences for the patient's. The SDM is not deciding what they would want for themselves — they are deciding what this specific person would have wanted, or failing that, what is genuinely best for this person.

When the Hierarchy Creates Family Conflict

The ranked list sounds orderly on paper. In real Ontario families, it often is not.

Consider a hypothetical: a man in his early 60s is incapacitated after a cardiac event. He separated from his wife three years ago but never divorced. Under the Health Care Consent Act, his separated spouse may still rank above his adult children as SDM, because the Act's definition of "spouse" includes married persons who have not yet obtained a divorce. If the separated spouse and the children disagree about treatment, that conflict is legally real — and the children may have no authority to override her.

Or imagine a blended family where the patient has children from two relationships who have not spoken in years. Both may rank equally. The Act says only one SDM acts at a time, and if equally ranked individuals cannot agree, the dispute may need to go to the Consent and Capacity Board.

Estranged relatives also complicate things. A sibling who has not spoken to the patient in a decade may outrank a close friend who has been a daily presence in their life. Friendship, no matter how deep, does not appear on the hierarchy at all.

The Consent and Capacity Board

When there is a genuine dispute — between SDMs at the same rank, or between an SDM and the patient's health care team — the Consent and Capacity Board (CCB) can step in. The CCB is an independent tribunal that hears applications under the Health Care Consent Act and the Substitute Decisions Act. It can appoint a representative, review an SDM's decision, and in some circumstances override a decision that was not made in keeping with the patient's known wishes or best interests.

That process takes time and carries emotional weight. Families navigating a medical crisis rarely want to add a tribunal proceeding to what they are already managing.

Why a Named Power of Attorney Changes Everything

A valid power of attorney for personal care, executed under the Substitute Decisions Act, places the person you trust at rank two on the hierarchy — immediately after a court-appointed guardian, and ahead of every family member. You choose that person. You can give them written guidance about your values and wishes. You can name an alternate in case your first choice is unavailable. You can restrict or expand their authority in specific ways.

None of that is possible if you leave the decision to the default hierarchy. The law will do its best to find someone appropriate, but "appropriate" under a statute and "the right person for me" are not always the same thing.