- Ontario law begins from a specific starting point: every person sixteen years of age or older is presumed to have the mental capacity to make their own health care decisions.
- The Health Care Consent Act sets out a two-part test.
- Under Ontario's scheme, the health practitioner who is proposing the treatment — most commonly a physician — is responsible for evaluating whether the patient is capable with respect to…
Whether you are sitting with a doctor weighing a difficult diagnosis, or you are the family member trying to understand why your loved one is refusing care, consent and capacity for medical treatment in Ontario is probably not something you expected to have to think about this carefully. The rules come from two provincial statutes — the Health Care Consent Act and the Substitute Decisions Act — and they matter enormously when a real medical decision has to be made right now.
Every Adult Starts with a Legal Presumption of Capacity
Ontario law begins from a specific starting point: every person sixteen years of age or older is presumed to have the mental capacity to make their own health care decisions. That presumption holds unless something triggers a formal assessment.
This matters for families in particular. The fact that someone is elderly, confused about some things, living with dementia, or even under sedation does not automatically strip them of the right to decide about their own treatment. Capacity is decision-specific and time-specific, and the law treats it that way deliberately.
What "Capacity" Actually Means in Law
The Health Care Consent Act sets out a two-part test. A person has capacity to make a treatment decision if they are able to:
- Understand the information that is relevant to the decision — what the treatment is, why it is being proposed, what the risks and benefits are, and what the alternatives look like; and
- Appreciate the reasonably foreseeable consequences of making that decision or of not making it — meaning they grasp how those facts apply to their own situation.
Understanding without appreciation is not enough. Someone who can recite a diagnosis back to a nurse but cannot connect it to their own body or circumstances may still be found incapable for that particular decision.
Who Assesses Capacity — and When
It is not a court that makes the initial determination. Under Ontario's scheme, the health practitioner who is proposing the treatment — most commonly a physician — is responsible for evaluating whether the patient is capable with respect to that specific decision. If they have concerns, they may bring in a formally trained capacity assessor, a regulated professional (often a psychologist, social worker, or physician with special certification) who conducts a structured evaluation.
Importantly, capacity can change. A person found incapable on a Tuesday morning after surgery may be fully capable by Thursday afternoon once medication is adjusted. Practitioners are expected to reassess when circumstances shift.
The Right to Refuse Treatment — Including Life-Sustaining Treatment
A capable adult in Ontario has the absolute right to refuse any treatment, including treatment that would keep them alive. This is not a loophole or an edge case; it is a cornerstone of the law. Health practitioners cannot override that refusal because they disagree with it or because family members are upset. Documenting and respecting a capable patient's informed refusal is a legal obligation, not a discretionary choice.
This is one reason why conversations about your wishes — ideally captured in a Power of Attorney for Personal Care — matter long before any crisis arrives.
When Someone Is Found Incapable: The Substitute Decision-Maker Hierarchy
If a person is found incapable of making a specific treatment decision, consent must come from a substitute decision-maker (SDM). Ontario law sets out an ordered list of who steps into that role, working from the top down:
- A guardian of the person appointed by the court
- A named attorney for personal care under a valid Power of Attorney for Personal Care
- A representative appointed by the Consent and Capacity Board
- A spouse or partner
- A child or parent (or a Children's Aid Society in certain circumstances)
- A parent with right of access only
- A sibling
- Any other relative
- The Public Guardian and Trustee, as the last resort
An SDM must make decisions based on what the incapable person would have wanted — their prior expressed wishes — not on what the SDM believes is best. If prior wishes are unknown, the SDM must act in the person's best interests.
The Consent and Capacity Board
The Consent and Capacity Board is an independent provincial tribunal that plays a specific and important role. It is not a court, and you do not need a lawyer to appear before it (though having one helps).
The Board can:
- Review a finding of incapacity — if you have been found incapable and you disagree, you can apply to the Board to have that finding reviewed.
- Review an SDM's consent or refusal — if a health practitioner believes an SDM is not acting in accordance with the patient's prior wishes or best interests, they can bring the matter to the Board.
- Appoint a representative to act as SDM when no one else in the hierarchy is available or suitable.
Proceedings can be initiated quickly when a treatment decision is urgent. The Board has the authority to substitute its own decision for that of the SDM if it concludes the SDM is not meeting the legal standard.
Fluctuating Capacity: Not All-or-Nothing
Capacity is not a light switch. A person may be capable of deciding whether to accept pain medication but incapable of consenting to a complex surgical procedure. They may be capable in the morning and not in the evening. A diagnosis of dementia does not equal a blanket finding of incapacity.
Health practitioners are required to assess capacity relative to the specific decision at hand. If there is any doubt, best practice is to reassess rather than assume incapacity.
How This Connects to Your Power of Attorney for Personal Care
A Power of Attorney for Personal Care gives your named attorney authority to make personal care decisions — including health care decisions — on your behalf. But that authority is not a standing override. The attorney's role activates only when you are incapable of making the specific decision yourself. Until that threshold is reached, you remain in control.
This is why the document needs to be carefully drafted and why your attorney needs to know your values and wishes in advance. A piece of paper alone is not enough.
The Emergency Exception
When a genuine emergency arises and delay would cause serious bodily harm or death, and it is not reasonably possible to obtain consent in time, a health practitioner may proceed with treatment without consent. This is a narrow exception, not a routine workaround. As soon as the emergency passes and consent can be obtained, the standard rules apply again.
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