In 1899, a German psychiatrist electrified the audience at a conference on hypnosis with a bold claim: He had turned a gay man straight.

All it took was 45 hypnosis sessions and a few trips to a brothel, Albert von Schrenck-Notzing bragged. Through hypnosis, he claimed, he had manipulated the man’s sexual impulses, diverting them from his interest in men to a lasting desire for women.

He didn’t know it, but he had just kicked off a phenomenon that would later be known as “conversion therapy”—a set of pseudoscientific techniques designed to quash LGBTQ people’s sexuality and make them conform to society’s expectations of how they should behave. Though it’s dismissed by the medical establishment today, conversion therapy was widely practiced throughout the 20th century, leaving shame, pain and self-hatred in its wake.

Homosexuality, especially same-sex relationships between men, was considered deviant, sinful and even criminal for centuries. In the late 19th century, psychiatrists and doctors began to address homosexuality, too. They labeled same-sex desire in medical terms—and started looking for ways to reverse it.

There were plenty of theories as to why people were homosexual. For Eugen Steinach, a pioneering Austrian endocrinologist, homosexuality was rooted in a man’s testicles. This theory led to testicle transplantation experiments in the 1920s during which gay men were castrated, then given “heterosexual” testicles.

Others theorized that homosexuality was a psychological disorder instead. Sigmund Freud hypothesized that humans are born innately bisexual and that homosexual people become gay because of their conditioning. But though Freud emphasized that homosexuality wasn’t a disease, per se, some of his colleagues didn’t agree. They began to use new psychiatric interventions in an attempt to “cure” gay people.

Some LGBTQ people were given electroconvulsive therapy, but others were subjected to even more extreme techniques like lobotomies. Other “treatments” included shocks administered through electrodes that were implanted directly into the brain. Robert Galbraith Heath, a psychiatrist in New Orleans who pioneered the technique, used this form of brain stimulation, along with hired prostitutes and heterosexual pornography, to “change” the sexual orientation of gay men. But though Heath contended he was able to actually turn gay men straight, his work has since been challenged and criticized for its methodology.

An offshoot of these techniques was “aversion therapy,” which was founded on the premise that if LGBTQ people became disgusted by homosexuality, they would no longer experience same-sex desire. Under medical supervision, people were given chemicals that made them vomit when they, for example, looked at photos of their lovers. Others were given electrical shocks—sometimes to their genitals—while they looked at gay pornography or cross-dressed.

“Although proponents of aversion therapy claimed ‘cure’ rates as high as 50 percent,” notes historian Elise Chenier, “these claims were never satisfactorily documented.”

LGBTQ people had long protested these cruel and scientifically dubious forms of “treatment,” but the concept that homosexuality was a disease was accepted by the majority of the medical establishment. This included the American Psychiatric Association, which considered homosexuality to be a psychiatric disorder.

But in the 1960s and 1970s, as a vocal gay rights movement took to the streets to demand equality, the profession began to turn its back on the concept that people could be “converted” to heterosexuality. In 1973, the APA removed homosexuality from the DSM, its influential manual of psychiatric disorders, and medical professionals began to distance themselves from techniques they had once embraced.

That wasn’t the end of attempts to turn gay people straight. As LGBTQ visibility increased, self-proclaimed “experts” and faith-based groups took over the practice themselves. They called their techniques “conversion” or “reparative” therapy, or advertised themselves as “ex-gay” ministries. Their methods varied, and included everything from talk therapy to exorcisms.

At “gay conversion” camps and conferences, LGBTQ people were isolated from family and friends, hypnotized, told to pray until their homosexuality subsided, instructed to beat effigies of their parents, mocked, coached on “proper” gender roles, and told their sexuality was unnatural and sinful.

For the people who underwent conversion therapy, shame and pain were an undeniable part of the process. “I read books and listened to audiotapes about how to have a ‘corrective and healing relationship with Jesus Christ,’” writes James Guay, a gay man who attended weekly therapy and conversion seminars as a teen. “These materials talked about how the “gay lifestyle” would create disease, depravity and misery. I was convinced that doing what I was told would change my attractions—and confused about why these methods supposedly worked for others but not for me.”

In some cases, people were psychologically and even sexually abused. Others committed suicide after “treatment.” Meanwhile, evidence that any of the techniques were effective remained nonexistent.

Though the concept of gay conversion still exists today, a growing tide has turned against the practice. Today, 13 states and the District of Columbia have laws that ban gay conversion therapy practices. Victims of facilities like JONAH, or Jews Offering New Alternatives for Healing, brought lawsuits for fraud. And Exodus International, an umbrella group that connected various conversion therapy groups and gay ministry organizations, closed down in 2013 after nearly 40 years of operations after its president, Alan Chambers, decided it’s impossible to change someone’s sexual orientation.

His opinion is shared by the medical establishment, which now accepts that homosexuality isn’t a matter of choice. For the 698,000 LGBT adults in the United States who have received conversion therapy—many against their will—the aftereffects of the practice are all too real. Studies have shown that attempts to change someone’s sexuality can result in everything from poor self esteem to increased suicide risk and mental health problems.

“These practices have no basis in science or medicine and they will now be relegated to the dustbin of quackery,” said California governor Jerry Brown as he signed a bill banning gay-to-straight therapy in the state in 2012. But for those who have been on the receiving end of the “therapy”—and those who still face pressure to receive it—its aftereffects can linger long past any bill or executive order.