A spokeswoman for Governor Herbert declined to comment on Wednesday but confirmed that the regulatory change went into effect on Tuesday night.

Conversion therapy, sometimes called “reparative therapy” or “sexual reorientation,” typically refers to the use of quasi-psychoanalytic methods, either in one-on-one or group therapy sessions, to try to change a person’s sexual orientation or gender identity.

It was not immediately clear how many minors are subjected to conversion therapy in Utah, which became the 19th state to ban the practice, according to the Human Rights Campaign.

Researchers at the Williams Institute at the University of California, Los Angeles law school estimated in 2018 that in the states that do not ban the practice, some 20,000 children between the ages of 13 and 17 would be subjected to conversion therapy from a licensed health care professional before they turned 18.

Conversion therapy has been linked to higher rates of suicide, homelessness and drug use among minors, according to the Human Rights Campaign.

Many states, including Colorado, Maine, Massachusetts and New York, have already moved to end conversion therapy on minors in recent years. Mr. Williams said he had received calls from other states looking to follow Utah’s model.

But the changes came as lawmakers in several states, including Utah, are also considering policies that activists say could harm L.G.B.T.Q. youth. Those include possible bans on providing transgender youth certain gender-related medical treatment, The Associated Press reported this week.

In Utah, the ban took a winding path before it went into effect.

A bill introduced in the state Legislature in February banning conversion therapy on minors stalled after conservative opposition.

Then, in June, Governor Herbert asked regulators to look into ways of addressing conversion therapy administratively.

The Church of Jesus Christ of Latter-day Saints, an influential force in Utah politics, expressed opposition in October to the proposed changes, saying they failed to protect individual religious beliefs and did “not account for important realities of gender identity in the development of children.”

But the church supported the final rule proposed in November.

“We are opposed to conversion therapy and our therapists do not practice it,” Marty Stephens, director of government relations for the church, said in a statement at the time. “However, we are grateful for the clarifications the new rule provides, and we support its adoption.”

Mr. Williams said it was difficult to estimate what proportion of conversion therapy in Utah was conducted by state-licensed therapists as opposed to parents or religious counselors.

The Williams Institute researchers estimated that 57,000 children between 13 and 17 years old nationwide would receive conversion therapy from “religious or spiritual advisers” before they turn 18.

Mr. Williams acknowledged that the new rule in Utah might not prevent all forms of conversion therapy, but said it was consistent with bans in other states.

He added that many people who practice conversion therapy try to avoid the label. But, he said, the new ban was the right first step.

“Our hope would be, as the state sets the standard, and if people become more educated about the harms of conversion therapy, that religious institutions or these kinds of ‘pray the gay away’ camps will back away,” he said.

Clifford Rosky, a law professor at the University of Utah who helped create the new ban, said that “no conversion therapy law applies to clergy members or parents talking to their children.” But he said the rule would indirectly deter people from pursuing conversion therapy.

“To have such a state that so deeply identifies with the Republican Party and conservative values step forward and say, ‘No, this practice is life-threatening, it’s harmful, it’s unnecessary, it’s ineffective and it must stop,’ is a profoundly important moment in the fight to ban conversion therapy,” he said.