[JohnnyChavello]

Not a source of law in Canadian courts, but the US Supreme Court officially endorsed the view that the Due Process Clause guarantees competent individuals the right to reject unwanted medical treatment as an aspect of individual liberty in Cruzan v. Glucksberg. Prior to this, most state and federal courts recognized it either on these grounds or as a right within the penumbras of constitutional protections of the right to privacy.

The interesting question from my point of view would be whether the government could regulate medical decisions for incompetent individuals against the wishes of the family. Don't know any cases directly on point, but in Cruzan, the Supreme Court held that the state could impose a standard of clear and convincing evidence on a family to establish that the decision to refuse medical treatment was what the incapacitated party wanted. The decision to reject life-sustaining medical treatment is a decision many people foresee potentially making, although a lot of people never clearly express their wishes; however, refusing psychiatric medication in the case of individuals committed to an institution is not a decision people are likely to go over with their families, nor would they be able to express specifically what they would and would not approve. Imposing a clear and convincing evidence standard in a case like that would probably be an insurmountable barrier.

I know nothing about Canadian law, but I would be shocked if the law were less protective of these decisions than they are in the US.