According to the principle of patient autonomy, patients have the right to be self-determining in decisions about their own medical care, which includes the right to refuse treatment. However, a treatment refusal may legitimately be overridden in cases where the decision is judged to be incompetent. It has recently been proposed that in assessments of competence, attention should be paid to the evaluative judgments that guide patients' treatment decisions.
In this paper I examine this claim in light of theories of practical rationality, focusing on the difficult case of an anorexic person who is judged to be competent and refuses treatment, thereby putting themselves at risk of serious harm. I argue that the standard criteria for competence assess whether a treatment decision satisfies the goals of practical decision-making, and that this same criterion can be applied to a patient's decision-guiding commitments. As a consequence I propose that a particular understanding of practical rationality offers a theoretical framework for justifying involuntary treatment in the anorexia case.