In an eight-to-one decision, the high court ruled against a law banning the discredited practice on free speech grounds.

The United States Supreme Court has ruled against a law in the state of Colorado that bans the controversial practice of “conversion therapy” for LGBTQ children, a discredited practice that has been linked to serious harm for participants.

Tuesday’s ruling was an eight-to-one decision, with two of the court’s three liberal justices joining its six conservatives in opposing the ban.

The court majority argued that restricting talk therapy could violate the free speech protections enshrined in the First Amendment of the Constitution.

“Once again, because the State has suppressed one side of a debate, while aiding the other, the constitutional issue is straightforward,” Elena Kagan, a left-leaning justice, wrote in a supporting opinion.

About two dozen US states have laws banning conversion therapy, which aims to “convert” the gender identity or sexual orientation of individuals to reflect heterosexual, cisgender norms.

Studies have linked the practice to higher rates of depression and suicidal thoughts for LGBTQ people.

Justice Neil Gorsuch, one of the court’s conservatives, argued that the First Amendment “stands as a shield against any effort to enforce orthodoxy in thought or speech in this country”.

That, in turn, prevents any state from limiting what a therapist might talk about with a patient, even if that therapist seeks to dissuade a child from their LGBTQ identity.

Only one justice, the left-leaning Ketanji Brown Jackson, cast a dissenting vote in Tuesday’s case.

She argued that the ruling “threatens to impair states’ ability to regulate the provision of medical care in any respect”, and she highlighted the dangers of conversion therapy to the health of LGBTQ youth.

In the lead-up to Tuesday’s ruling, Christian counsellor Kaley Chiles successfully argued that the Colorado law banned her from offering voluntary, faith-based talk therapy for children. Her case was supported by the administration of President Donald Trump.

Colorado, meanwhile, maintained that, while its law barred any “practice or treatment” to “convert” LGBTQ youth, discussions about religion, gender and sexuality were in general not prohibited.

Talk therapy, it argued, is also different from other forms of speech, as it represents a form of healthcare. Colorado maintained it had the ability to regulate it as a result.

Nobody has been sanctioned under Colorado’s law, which was passed in 2019. Tuesday’s ruling will likely make similar laws more difficult to enforce. LGBTQ advocates slammed the decision as a step backwards.

“This is a dangerous practice that has been condemned by every major medical association in the country,” Polly Crozier, director of family policy at the advocacy group GLAD Law, said in a statement.

“Today’s decision does not change the science, and it does not change the fact that conversion therapists who harm patients will still face legal consequences.”