Under certain circumstances such as terminal illness the patient can have the right to refuse life saving medical treatment or to have such life sustaining medical treatment withdrawn.
The courts have allowed withdrawal of life support measures when the patient was in a persistent vegetative state despite stable conditions with still longer life expectancy into the future.
Patients sometimes execute living wills to specify the intention to refuse life prolonging medical treatment in the event of terminal illness.
Through health care proxy mechanism, an individual designates another person to take his health care decisions when he would be rendered incapable. In fact the health care proxy has the same rights to decline any unwanted medical treatment to extend life like the principal himself if he were in a mentally sound condition.