For a medical treatment to be legal, clinicians must obtain the informed consent of the patient or operate within a limited set of circumstances.
Three elements make up informed consent (Ministry of Health, 1998 [pdf]):
- The patient must have the capacity to give consent.
- The practitioner must provide full information.
- The patient's consent must be freely given.
Historically Pākehā society regarded children as the property of their parents. The modern view is that children have a degree of autonomy, and that the courts can sometimes intervene to serve the child's best interests.
At common law, the child's autonomy and capacity to consent to treatment was carefully considered in the Gillick v West Norfolk and Wisbech AHA case before the House of Lords. The Gillick decision was based on the principle that as children mature they grow in competence and autonomy. Therefore a child's capacity to consent will depend on their individual circumstances and the nature of the treatment. The clinician must determine whether the child patient has the understanding and maturity to form a balanced judgement. The case established the legal concept of "Gillick" competence. The decision has been applied by NZ courts and is generally accepted as authoritative (Ministry of Health, 1998) [pdf].
The recent Bell v Tavistock case before the UK High Court examined the issue of Gillick competence, the child's best interest, and pubery blocking treatment in detail. The court ruled that children under the age of 16 are unlikely to understand the impacts of puberty suppression and cross-sex hormones.
For more analysis of the Bell Judgement see:
- High Court ruling that children should not be given puberty blockers: SSAUK statement
- Puberty Blockers and Parental Consent
Treating gender dysphoric adolescents with puberty blockers carries a risk of permanent impacts to cognitive development amongst other harms. Puberty between the ages 10-16 may be a critical window for brain maturation and supressing puberty for all or some of this period could have permanent effects on cognitive function. The treatment lacks high-quality evidence of beneficial impacts.
A case study of a Brazilian child demonstrated a 10 point drop in IQ following puberty supression (Schneider et al., 2017). An animal study demonstrated a large and sustained reduction in long-term spatial memory following pubertal supression (Hough et al., 2017).
Exemplar consent forms published by the University of Waikato do not mention these risks.
The BBC has reported on clinicians at GIDS who believed that some parents of children at GIDS had anti-homosexual attitudes. These parents seemed to prefer a transgender child with the appearance of heterosexuality to a gender-non-conforming homosexual child. Even assuming trans-identified children in a homophobic social environment did have the capacity to consent, it is doubtful that their consent "become a boy or girl" could be freely given. The early medical intervention approach reccomened in the Waikato guidelines leaves little room for the clinician to assess coercion in the child's social environment.
Updated 05-04-2021: In another case the UK High Court has ruled that parents can consent to puberty blockers in the absence of the child's consent. However, the Bell judgement still stands and GIDS have stated in court  that they “[could not] conceive of any situation where it would be appropriate to administer blockers on a patient without their consent”. Its unclear how this judgement will affect GIDs policy on puberty blockers. The text on this page has been modified to reflect the lack of clarity.