People can assume only risks that they know about. For most commonplace activities, such as driving a car, the risks are well known and are implicitly assumed by engaging in the activity. It is possible to assume implicitly the risks of medical care. For example, a physician undergoing general anesthesia would be assumed to know that general anesthesia carries a risk of anoxic brain damage. He or she would implicitly assume this risk without the need for an explicit informed consent.

Most patients do not have the background medical knowledge to assume specific risks of treatment implicitly. Prior to the advent of informed consent, the patient was assumed to know that medical treatment was risky. Since the person had sought treatment knowing that it was risky, he or she was assumed to have accepted that the risk of treatment was less than the risk of the medical condition. The law was not concerned with the particular form that a risk might take.

Advances in medical technology have caused a proliferation of choices in medical therapy. Patients are no longer limited to the choice between treatment or no treatment. This undermines the theory that the patient has accepted that the undifferentiated risks of medical therapy outweigh the risks of the condition. With many possible therapies for a given condition, the courts have rejected this implicit assumption of risk. A patient must now be told of the risks that he or she is assuming. The more particularized the information is about the potential adverse consequences of a treatment, the more effective is the assumption of risk.