A federal judge has temporarily blocked California from a new law that bans licensed psychotherapists from attempting to change the sexual orientation of young people. The judge’s actions only apply to three providers that appealed to him to overturn the legislation.

Judge William Shubb ruled that the First Amendment rights of psychiatrists, psychologists and other mental health professionals who engage in “reparative” or “conversion” therapy overrule any concerns that such practices are harmful to young people.

“Even if SB 1172 is characterised as primarily aimed at regulating conduct, it also extends to forms of (conversion therapy) that utilize speech and, at a minimum, regulates conduct that has an incidental effect on speech,” Judge Shubb wrote in his judgement.

He also dismissed claims that such therapies can put young gay people at risk of suicide or depression saying that such claims are from “questionable and scientifically incomplete studies.”

In September, campaigners and medical professionals welcomed California Governor Jerry Brown’s decision to ban teenagers from accessing discredited treatments that seek to reject an LGBT identity.

When the law, signed in by Governor Brown, comes into effect on 1 January 2013, California will become the first to outlaw the practice for people under the age of 18 in America.

Governor Brown said in a statement that gay “conversion therapy” had “no basis in science or medicine,” and that it would be “relegated to the dustbin of quackery”.

The judge’s ruling last night only applies to three people: psychiatrist Anthony Duk, marriage and family therapist Donald Welch, and Aaron Bitzer, an ex-gay psychotherapy student. Campaigners said though that others could apply for the ruling to be extended to them.

However, the exemptions only apply until a full trial is held on the subject although pre-judging the outcome, Judge Shubb said that he believed that the law will be struck down on constitutional grounds.

National Center for Lesbian Rights Legal Director Shannon Minter said: “We are disappointed by the ruling, but very pleased that the temporary delay in implementing this important law applies only to the three plaintiffs who brought this lawsuit. We are confident that as the case progresses, it will be clear to the court that this law is fundamentally no different than many other laws that regulate health care professionals to protect patients.”

Last week, four gay men in New York filed a lawsuit accusing the New Jersey-based Jewish gay cure service JONAH group of falsely offering “conversion therapy”, which was not effective, and should not be advertised as a “cure” for being gay.