In parallel with advances in drug therapy, anesthesia, and surgery, there has been a shift in bioethics from a paternalistic ethic governed by doctors to one based on the patient's autonomy. The notion of consent to medical procedures and treatment is a reflection of this, and in many countries, this consent is now established in law. The terms “informed” and “patient's consent” were perhaps first coupled in the 1957 case of Salgo versus Leland Stanford Jr. University Board of Trustees. The plaintiff, paralyzed after myelography脊髄造影, had not been informed by his doctor that paralysis was a possible risk of this procedure. He won although the doctor had committed no mistake because the doctor failed in his duty of disclosure. The court found that if the patient had been properly informed he would have refused myelography .
From a legal perspective, any consent, if it is to be valid, has to meet three independent preconditions, all of which have to be taken into account simultaneously. Consent may be deemed invalid if it has been obtained by deception or coercion; if it does not comply with formal procedures; or if the person lacks the capacity to consent by virtue of mental illness. The weaker a patient's personal competence, the more stringent the procedural considerations must be. This is to avoid coercion or exploitation, and to ensure that the disclosure of information has taken into account the patient's capacity for understanding and evaluating the situation. Equally, certain radical medical procedures call for stringent requirements to be met on personal and procedural competence. Such preconditions may be specifically formulated, as in Norway's abortion, sterilization, and transplantation legislation.
These preconditions reflect a general principle of international health law, illustrated by the 1973 US case of Kaimowitz vs Michigan Department of Mental Health. Here the court found that even though a difficult psychiatric patient possessed the competence required to consent to ordinary surgical procedures, and even to “accepted neurosurgical procedures”, his competence would not be sufficient for him to consent to experimental neurosurgical procedures characterized as “dangerous, intrusive, irreversible, and of uncertain benefit to the patient and the society”.
The requirement for informed and voluntary consent is not always applicable to non-invasive medical procedures. In most cases, staff should be able to decide on the necessary procedures without having the patient's expressed consent, after having provided information to the patient. They must, however, respect a patient's rejection of any specific examinations or treatments. When the treatment offered is invasive, the doctor will have the responsibility for providing the patient with all necessary information―about the risks and the alternative treatments and their probable consequences.