Substitute Decision Maker in Ontario: Who Decides When Your Parent Can’t?
Your parent is in the hospital. The doctor is asking about surgery, about treatment options, about discharge plans. But your parent is confused — maybe from dementia, maybe from a stroke, maybe from medication. They can’t make these decisions right now. The doctor turns to you and asks: “Are you the substitute decision maker?”
And you have no idea what that means or whether you are.
What Is a Substitute Decision Maker?
A substitute decision maker (SDM) is the person legally authorized to make decisions on behalf of someone who has been found incapable of making those decisions themselves. In Ontario, this is governed by the Health Care Consent Act and the Substitute Decisions Act.
There are two types of SDM:
- SDM for health/personal care: Makes decisions about medical treatment, housing, nutrition, safety, hygiene
- SDM for property/finances: Makes decisions about money, investments, real estate, bills
The same person can be both, or they can be different people. And here’s the thing most people don’t realize: you might already be someone’s SDM without knowing it.
How Ontario Determines the SDM
Option 1: Your parent named someone (Power of Attorney)
If your parent signed a Power of Attorney for Personal Care, the person they named IS the SDM for health and personal care decisions. If they signed a Continuing Power of Attorney for Property, that person manages finances.
This is the best scenario — your parent chose who they trust while they still had capacity to choose. The POA activates when your parent is found incapable (through a capacity assessment or a health practitioner’s determination).
Option 2: No POA exists — the hierarchy
If your parent never signed a POA (and most people haven’t), Ontario law has a ranked list that determines who becomes the SDM. For health care decisions, the hierarchy is:
- Guardian (court-appointed) — if one exists
- Attorney for personal care (POA) — if one exists
- Representative appointed by the Consent and Capacity Board
- Spouse or partner
- Adult child (or parent of a minor)
- Parent with right of access
- Sibling
- Any other relative
- Public Guardian and Trustee (government — last resort)
The person must be:
- Capable themselves
- At least 16 years old
- Available and willing to act
- Not prohibited by court order
If there are multiple people at the same level (e.g., three adult children), the one who is present and willing acts as SDM. If they disagree? That’s where it gets complicated.
What the SDM Actually Does
Being an SDM isn’t about what YOU want for your parent. Ontario law is very specific about this. The SDM must follow these rules, in order:
Rule 1: Follow prior capable wishes
If your parent expressed wishes while they were still capable — “I never want a feeding tube,” “Don’t put me in a nursing home,” “I want everything possible done to keep me alive” — the SDM MUST follow those wishes, even if you disagree.
Rule 2: If no wishes are known, act in their best interests
Best interests means considering:
- Their values and beliefs (religious, cultural, personal)
- Their current wishes, if they can express any (even if legally “incapable,” their voice still matters)
- Whether the proposed treatment will improve their condition or quality of life
- Whether the expected benefit outweighs the risk
Best interests does NOT mean “what’s most convenient for the family.” An SDM who makes decisions based on their own convenience rather than the patient’s best interests is acting illegally.
Common SDM Situations
Consenting to medical treatment
Your parent needs surgery. They can’t understand the risks. The doctor explains the procedure to YOU, and you consent (or refuse) on their behalf. This happens every day in hospitals across Ontario.
Deciding where your parent lives
If your parent is found incapable of personal care decisions, the SDM can decide that they move to a retirement home or long-term care home — even if your parent doesn’t want to. This is one of the hardest decisions an SDM ever makes.
But remember Rule 1: if your parent clearly stated they never wanted to leave their home, you need to honour that as much as safely possible. Maximum home care first, residential care only when home is truly unsafe.
Managing finances
If you’re the SDM for property, you manage your parent’s bank accounts, pay their bills, file their taxes, and make investment decisions. You must keep records of every transaction. This is a fiduciary duty — you can be held legally accountable if you mismanage their money.
End-of-life decisions
The most gut-wrenching role. If your parent is dying and can’t communicate, you make decisions about palliative care, resuscitation, life support, and comfort measures. If they have an advance directive or expressed wishes while capable, follow those. If they didn’t — you do your best with what you know about who they were.
When Siblings Disagree
This is the #1 source of family conflict in elder care. One sibling thinks Dad should stay home. Another thinks he needs a nursing home. A third hasn’t visited in two years but has strong opinions on the phone.
Ontario law is clear: only ONE person is the SDM. The highest-ranking person on the hierarchy who is available and willing. Other family members don’t get a vote — legally.
In practice, most families try to reach consensus. But if they can’t, the SDM’s decision stands. A dissenting family member can:
- Apply to the Consent and Capacity Board to replace the SDM
- Apply to the court for guardianship
- Contact the Office of the Public Guardian and Trustee if they believe the SDM is acting improperly
None of these are quick processes. In an emergency, the hospital proceeds with the available SDM’s consent.
The Difference Between SDM, POA, and Guardian
These terms get mixed up constantly. Here’s the simple version:
- Power of Attorney (POA): A document your parent signs WHILE CAPABLE, naming someone to act for them IF they become incapable. It’s a plan-ahead tool.
- Substitute Decision Maker (SDM): The person who actually makes decisions when someone is incapable. This might be the POA holder, or it might be determined by the hierarchy if there’s no POA.
- Guardian: A person appointed BY THE COURT to make decisions. Guardianship is only needed when there’s no POA and the hierarchy doesn’t work (e.g., no available family). It’s expensive ($5,000-$15,000+ in legal fees) and time-consuming.
The lesson: Get your parent to sign a POA while they still can. It avoids the hierarchy confusion, avoids guardianship court costs, and ensures THEY choose who decides for them. Read our guide on Power of Attorney for elderly parents.
Protecting Yourself as an SDM
Being an SDM can feel like a target on your back. Other family members may question your decisions. Your parent may resent you. You may doubt yourself constantly.
Protect yourself:
- Document everything. Keep notes on every decision: what it was, why you made it, what information you had. If anyone ever challenges you, these records are your defense.
- Follow the rules. Prior capable wishes first, then best interests. If you can show you followed the legal framework, you’re protected.
- Consult professionals. Don’t make big decisions alone. Talk to the doctor, a social worker, an elder law lawyer. Their input supports your decision-making and creates a paper trail.
- Get support. This role is emotionally draining. Caregiver burnout affects SDMs just like hands-on caregivers. Talk to someone — a counsellor, a support group, a trusted friend.
If Your Parent Still Has Capacity — Act Now
If you’re reading this proactively — your parent is still lucid, still making good decisions — this is the time to act. Have the conversation. Get the documents signed:
- Power of Attorney for Personal Care — who makes health and living decisions
- Continuing Power of Attorney for Property — who manages money
- Advance directive / living will — your parent’s specific wishes for medical care
An elder law lawyer can draft all three for $500-$1,500. It’s the best money you’ll ever spend on future peace of mind.
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