We now understand that informed consent itself must be:
The discovery of the harrowing atrocities of Joseph Mengele and his experiments on children and the mentally handicapped in Nazi Germany led to the Nuremberg Code, in which the rights of individual patients to certain protections were advanced. The right to voluntary informed consent was among them. This was strengthened by the Declaration of Helsinki.
In the early 1900s in the US, patients who suffered harm at the hands of surgeons who had taken it upon themselves to perform additional surgery without bothering to wake the patient from general anesthesia and review how the first surgery had progressed were sued, and decisions made in the Supreme Court began to set precedent for informed consent in the US.
Under the Council for International Organizations of Medical Sciences (CIOMS, International Ethical Guidelines for Health-related Research Involving Humans), informed consent can only be given by a competent individual who:
Further, this is considered to be a 4-step process:
A physician violates his duty to his patient and subjects himself to liability if he withholds any facts which are necessary to form the basis of an intelligent consent by a patient to a proposed treatment.