A federal judge on Tuesday struck down Arkansas' ban on gender-affirming treatment for transgender youth, dealing the strongest blow yet to a state prohibition on such care.

In an 80-page ruling, Judge James M. Moody Jr. said that the state's "Save Adolescents from Experimentation Act" violated the US Constitution and that the 2021 law cannot be enforced by state officials.

"Rather than protecting children or safeguarding medical ethics, the evidence showed that the prohibited medical care improves the mental health and well-being of patients and that, by prohibiting it, the State undermined the interests it claims to be advancing," the judge wrote.

"Further, the various claims underlying the State's arguments that the Act protects children and safeguards medical ethics do not explain why only gender-affirming medical care -- and all gender-affirming medical care -- is singled out for prohibition," he continued. "The testimony of well-credentialed experts, doctors who provide gender-affirming medical care in Arkansas, and families that rely on that care directly refutes any claim by the State that the Act advances an interest in protecting children."

Gender-affirming care spans a range of evidence-based treatments and approaches that benefit transgender and nonbinary people. The types of care vary by the age and goals of the recipient, and are considered the standard of care by many mainstream medical associations.

Though the ruling only applies to Arkansas' ban, it represents a significant victory for LGBTQ advocates, who have been bringing legal challenges over the last few years to similar laws that have been enacted in GOP-led states.

The case marked the first time a federal judge has had the chance to receive extensive evidence and briefing in a challenge to a ban on gender-affirming care. Moody had temporarily blocked the law from going into effect in July 2021, and an eight-day trial took place last year in the case. Similar suits have been brought in Alabama and Tennessee.

"This victory shows that these laws, when tested by evidence, are indefensible under any standard of constitutional review. We hope that this sends a message to other states about the vulnerability of these laws and the many harms that come from passing them," said Chase Strangio, an attorney at the American Civil Liberties Union who helped represent the plaintiffs in the case, in a statement.

Arkansas plans to appeal the ruling to the US Court of Appeals for the 8th Circuit. Last August, a three-judge panel on the appeals court allowed Moody's preliminary injunction to stand.

"I am disappointed in the decision that prevents our state from protecting our children against dangerous medical experimentation under the moniker of 'gender transition,'" said Arkansas Attorney General Tim Griffin in a statement.

The lawsuit had been brought two years ago by four transgender adolescents in Arkansas and their families, as well as two doctors who provide gender-affirming care to trans youth in the state.

When Arkansas enacted the law in 2021, it became the first state in the nation to prohibit gender-affirming care for trans youth. The state's then-Republican governor had initially vetoed the measure, but state lawmakers later overrode his veto.

In his ruling, Moody acknowledged that there were some "potential risks" associated with gender-affirming treatments, an argument that had been advanced by proponents of the law. But, he wrote, "For many adolescents the benefits of treatment greatly outweigh the risks."

"There is nothing unique about the risks of gender-affirming medical care for adolescents that warrants taking this medical decision out of the hands of adolescent patients, their parents, and their doctors," the judge wrote.

Under the now-blocked law, young people would have not been able to access puberty-blockers, a treatment option for transgender youth that is used to prevent the onset of puberty. The measure also banned ​so-called cross-hormone therapy,​ a gender-affirming treatment that allows for trans people to ​change their physical appearances to be more consistent with their gender identities. The legislation made what it calls an "exception" for some intersex people with unspecified chromosomal makeup and hormone production, and those with difficulties resulting from previous gender-affirming treatments.

LGBTQ and medical advocates had strongly opposed the measure, which they feared could have significant negative impacts on trans youth, who have a much greater risk of attempting suicide, according to the US Centers for Disease Control and Prevention.

Moody's ruling seemed to recognize those fears.

"Conclusions cannot be drawn from any single study (in any area of medical research), but the body of medical research as a whole shows that gender-affirming medical treatments are effective at improving mental health outcomes for adolescents with gender dysphoria," he wrote.

This story has been updated with additional details Tuesday.