The move, announced by the governor’s office, marked a major victory for gay rights advocates who say so-called conversion therapy, also called reparative therapy, has no medical basis because homosexuality is not a disorder.

Brown said in a short message on Twitter that he supported the bill because it “bans non-scientific ‘therapies’ that have driven young people to depression and suicide.”

The bill’s sponsor, state Senator Ted Lieu, a Democrat from Torrance, said the law was a gesture of remembrance for a man who committed suicide after undergoing the therapy.

The measure prohibits children and teens under 18 from undergoing sexual orientation change efforts. It received support from the California Psychological Association and the California Board of Behavioral Sciences, among others.

“LGBT (lesbian, gay, bisexual and transgender) youth will now be protected from a practice that has not only been debunked as junk science, but has been proven to have drastically negative effects on their well-being,” Human Rights Campaign President Chad Griffin said in a statement.

He urged other states to follow California’s lead.

Lieu said the psychiatrist who pioneered the therapy, Dr. Robert Spitzer, has since renounced it and has apologised to the gay and lesbian community.

“If anyone had any doubts such practices were evil, they need only listen to accounts of victims who went through this abusive practice,” Lieu said in a statement.

During the legislature’s consideration of the bill, people who had undergone the therapy as minors testified about why they wanted the practice banned.

“As a young teen, the anti-gay practice of so-called conversion therapy destroyed my life and tore apart my family,” witness Ryan Kendall told legislators.

Several openly gay legislators gave emotional speeches in support of the measure, sharing how they were bullied because of their sexual orientation as youths.

All major medical and mental health organisations including the American Medical Association and the American Psychiatric Association have denounced the practice, supporters said.

Opponents said the bill encroached on the rights of parents to make choices for their children. They also said politicians should not regulate what they considered to be a matter for medical boards to decide.

The measure will take effect on January 1.