Alternatively, the doctrine of implied consent permits treatment in limited cases, for example when an unconscious person will die without immediate intervention. If an individual is considered unable to give informed consent, another person is generally authorized to give consent on their behalf-for example, the parents or legal guardians of a child (though in this circumstance the child may be required to provide informed assent) and conservators for the mentally disordered. Obtaining informed consent is not always required.

Impairments to reasoning and judgment that may preclude informed consent include intellectual or emotional immaturity, high levels of stress such as post-traumatic stress disorder or a severe intellectual disability, severe mental disorder, intoxication, severe sleep deprivation, dementia, or coma. To give informed consent, the individual concerned must have adequate reasoning faculties and possess all relevant facts. Informed consent requires a clear appreciation and understanding of the facts, implications, and consequences of an action. Within the US, definitions of informed consent vary, and the standard required is generally determined by the state. This principle applies more broadly than healthcare intervention, for example to conduct research and to disclose a person's medical information. In most systems, healthcare providers have a legal and ethical responsibility to ensure that a patient's consent is informed. Pertinent information may include risks and benefits of treatments, alternative treatments, the patient's role in treatment, and their right to refuse treatment. Informed consent is a principle in medical ethics and medical law and media studies, that a patient must have sufficient information and understanding before making decisions about their medical care.

Example of informed consent document from the PARAMOUNT trial

Consent by A.J. Rose