Therapy that seeks to change minors' sexual orientation or gender identity is now illegal in Colorado. Gov. Jared Polis, the first openly gay man ever elected governor in the U.S., signed the ban into law on Friday.

"Colorado has joined a growing list of states that have banned so-called conversion therapy. It’s a horrific practice that has long been widely-discredited by medical and mental health professionals and has scarred many survivors for life," Polis said in a statement emailed to NBC News. "Today Colorado took an important step forward in recognizing our diversity as a strength. These bills truly underscore the idea that Colorado is a state where everyone can be their true selves and live the life they want.”

Colorado is now the 18th U.S. state — and the fourth this year — to ban the controversial practice. Just this week, Maine's governor signed a ban.

Research shows so-called conversion therapy, which treats being gay or transgender as a mental illness, increases the risk of suicide, drug abuse and depression among teens. A long list of health associations, including the American Medical Association and the American Psychological Association, have spoken out against the practice, which is also known as "reparative therapy" or "ex-gay therapy."

In the statement shared with NBC News, Polis said he's thrilled to launch LGBTQ Pride Month in June by outlawing what he called a "tortuous practice" harming children.

Polis also signed into law on Friday a bill making it much easier for transgender Coloradans to update the gender on their birth certificates, identification documents and driver's licenses.

Daniel Ramos, executive director of One Colorado, a statewide LGBTQ advocacy group, applauded the "strong bipartisan support" both bills received, which he said "further demonstrates that LGBTQ equality should be a nonpartisan issue."

"Colorado will continue to make history as our country’s first openly gay Governor, Jared Polis, signs our pro-equality agenda into law to send a strong message that Colorado is a state that is open to all," Ramos continued.

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