Advance decisions and proxy decision-making in medical treatment and research 13 November 2007 June 2007 This guidance covers the law and ethical issues involved in competent individuals making advance decisions about their later medical treatment and proxy decisions about medical treatment made by other people on behalf of adults who lack mental capacity. When they are mentally competent, patients decide for themselves whether or not to accept the medical treatments recommended by health professionals. This guidance is about what happens when that mental ability to make a valid decision is lost.