Amazon has removed English-language books by a man largely considered “the father of conversion therapy” from its site following mounting pressure from LGBTQ activists.

Dr. Joseph Nicolosi, founder of the now-shuttered Thomas Aquinas Psychological Clinic, as well as the National Association for Research and Therapy of Homosexuality (NARTH), authored several how-to guides directed to parents of LGBTQ youth, including “A Parent’s Guide to Preventing Homosexuality.” His books are some of the most well-known works about conversion therapy, the pseudoscientific practice of trying to change a person’s sexual orientation or gender identity.

“I would say many survivors of conversion therapy could trace their trauma to Nicolosi,” Sam Brinton, head of advocacy and government affairs at The Trevor Project and a survivor of conversion therapy, told NBC News. “His work lent credibility under the guise of ‘science’ to conversion therapy, even though the practice has been disputed and discredited as dangerous and harmful by medical experts.”

Nicolosi died in 2017 from complications of the flu, but the misconception that conversion therapy is a legitimate practice lives on.

According to The Trevor Project’s 2019 National Survey on LGBTQ Youth Mental Health, 2 in 3 LGBTQ youths reported that someone tried to convince them to change their sexual orientation or gender identity, and youths who have undergone conversion therapy are more than twice as likely to attempt suicide as those who did not.

Though activists have been urging Amazon to remove the books for several months, as evinced by a Change.org position that has amassed more than 82,000 signatures as of Wednesday afternoon, one man in particular made it his mission to prevent the company from selling the books.

Roger Alan first learned about Nicolosi’s books from Peterborough International Christian Centre, a church in his native United Kingdom, around three months ago. The church planned to show “Flying Blind,” a video about conversion therapy, to its parishioners, and when met with widespread criticism, it defended the screening by referring to Nicolosi’s work.

While the church ultimately canceled the event, the books remained available for purchase on Wordery, an online bookseller, and Amazon.

“I’d been through something myself when I was younger,” Alan, who is gay, said. “I had to talk to someone who told me ‘there’s no such thing as being gay.’ It took me forever to understand my sexuality, and it was a really difficult time for me.”

Alan said he reached out to both sites and called for the books’ removal. Wordery removed the books the next day, but Amazon informed him that his request would be passed along to the “relevant team.”

After a month had passed with no action, Alan reached out the British Psychological Society and the American Psychological Association — organizations that have acknowledged the harm associated with conversion therapy — in an attempt to gain medical and legal context to strengthen his request. The BPS calls conversion therapy “unethical” and the APA says it has "serious potential to harm young people because they present the view that the sexual orientation of lesbian, gay and bisexual youth is a mental illness or disorder, and they often frame the inability to change one's sexual orientation as a personal and moral failure."

Alan also revealed that he reached out to strangers via Reddit, Facebook and other social media, urging them to leave negative reviews of Nicolosi’s books on Amazon. He spoke to approximately 15 people he didn’t know on the phone about why he thought the books were dangerous — all the while juggling his jobs as a home insurance agent and a bookseller.

“I kept speaking to other people at Amazon and they were sympathetic, but all they could tell me was that they’d pass along the info,” Alan said. “I wasn’t really getting anywhere.”

Then, three months after he submitted his first request, something changed. While Alan was completing his daily ritual of searching for Nicolosi’s books on Amazon on Tuesday, he realized the English-language versions of the books were no longer available (some of the works can still be found in Spanish and Portuguese).

Amazon has not contacted Alan about its removal of the books, but the company confirmed to NBC News that several titles by Nicolosi are no longer available and that it reserves the right to not sell books that go against its content guidelines.

Last December, Amazon removed a gay conversion therapy app from a religious group called Living Hope Ministries, which included anti-gay podcasts, articles and devotionals.

“We were feeling quite hopeless,” Alan said. “These books were outrightly lying to parents on how they could cure their children from being gay or trans and essentially teach ways you can mentally and physically abuse your child. But now that the books have been removed, we’re overjoyed.”

Brinton believes that while the removal of Nicolosi’s books won’t stop conversion therapy, it will help the public better understand the dangers of the practice.

“These books will still be accessible and will still be a risk for youth,” Brinton, the co-founder of 50 Bills 50 States, the largest campaign to protect LGBTQ youths from conversion therapy in the U.S., said. “But you can compare removing them to the surgeon general announcing smoking is dangerous: People now know the side effects of the practice.”

“The best way to save lives is to pass legislation,” Brinton added, noting that in the last 30 months, 13 laws have been passed protecting minors against conversion therapy. Currently 18 states, along with the District of Columbia, ban the practice on minors.

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