The law has increasingly emphasised that a patient must be given adequate information to make an informed decision whether to agree to a medical procedure. This includes:

Most of the cases have concerned the type and amount of information that needs to be given about the potential risks of a proposed procedure.

The High Court said in Rogers v Whitaker [1992] HCA 58 a doctor must warn a patient of risks that are "material", and a risk is material if:

Therefore, the test of what risks are material is patient-centred, and this approach has not been altered in relation to information-giving by the "so-called" tort law reforms.

Essentially, this means a patient should be warned of risks that are likely to be significant to that person. This will depend upon:

As stated, the test is whether the risk in question is so serious, or so likely to occur, that it is likely to influence the decision of an ordinary person in the patient's position whether to agree to the procedure in question; or whether the doctor should know that the risk would be significant for the particular patient.

Ultimately, this may have to be decided by a court according to the circumstances of a particular case. There is no ready guide. In any event, practitioners should always try to respond truthfully and adequately to patients' questions. Therefore, as a health consumer, it is advisable to question health professionals in order to resolve any doubts about the consequences of a treatment or procedure.

There are several situations in which less information may be justifiable.

The first is an emergency. Here, treatment may be given without any information or consent, if it is necessary to protect the patient's life or health.

If, for instance, a patient is unconscious, a health professional may perform whatever procedures are reasonably necessary in the circumstances. It is not necessary to obtain the consent of the patient's next of kin, although where practicable, that is generally done as a courtesy, and relatives do have lawful authority to consent in some circumstances (see: "Capacity to consent", below).

The second case in which less information may be required is when the patient waives the right to be given information. This would justify the practitioner not fully discussing the risks of a proposed procedure. However, the patient must still be given sufficient information about the procedure to give an effective consent to it.

The third situation is a doctor's limited discretion therapeutic privilege not to disclose information where they have reasonable grounds to believe disclosure of the information may itself harm the patient (e.g. if the patient is suicidal or mentally ill). Even in this case, however, a doctor may not be justified in withholding information if a patient asks a specific question.

Consent may be express or implied. Hospitals usually require patients undergoing surgery to sign a consent form which often states the patient has been given information about the procedure in question and has consented to it. The fact that a person has signed such a form is evidence they were informed and consented, but it is not conclusive evidence. A court may still examine the circumstances in which the form was signed to determine whether the person was really told and understood.

In most cases, however, consent is implied from a person's actions, such as rolling up a sleeve to receive a flu vaccine. This type of consent is generally effective, though the law may be less ready to accept that consent was present if the procedure poses a substantial risk to the patient.

Consent must be freely given. A person should not be pressured by a health professional into deciding on a particular course of treatment.

The principles that people may not be given medical treatment without their consent, and they are entitled to adequate information to make an informed choice, apply to competent adults (that is, to people over 18 who are able to understand their condition and the options for treatment).

If the person is a child (under 18), either parent or a guardian may generally consent to a medical procedure, and the parent or guardian is entitled to the same information as an adult patient. However, an older child may also be able to consent if sufficiently mature to understand the procedure. This will depend on the child's age and level of maturity and also the particular procedure. Even relatively young children can consent to simple procedures for their own good, such as a vaccination. On the other hand, greater maturity and understanding will be required for procedures that are risky or contentious, such as contraception.

In the case of non-therapeutic sterilisation of a mentally handicapped minor, court authority is required; the parent alone cannot consent.

People who are seriously physically impaired or who have an intellectual disability or mental illness may not be able to consent to medical treatment. Again, this will depend on the patient's level of understanding and ability to communicate, and the nature of the procedure. It is presumed that patients with an intellectual disability are able to make their own medical decisions unless the doctor considers, after careful consideration, the patient cannot understand.

If they are not competent to decide, consent must be sought from someone else. If the person is over 18 and incapable of giving consent, consent may be given by a "person responsible" under the Guardianship and Administration Act 1986 (Vic) Part 4A ("GAA"); see: "Consent to medical treatment", in Chapter 16*6 Guardianship and Administration.