If things had gone differently, both Bob*, 41, and Jimmy, 31, might not be on the national sex-offender registry. Bob wouldn't have done four years in prison for molesting a young girl and buying child porn, and Jimmy wouldn't have spent most of his twenties in jail on endless charges of exposing himself to unsuspecting women in cars.

"I pulled up to this woman once and was like, 'Hey,' to get her attention," Jimmy recalls of one of his flashing incidents. "She just looked at me and started laughing and said, 'You got something wrong with you,' and I thought, 'Yeah, I think I do.' I knew it was wrong. I was embarrassed.”

"Life is more carefree," says one chemically castrated sex offender. "I can plan for events five or six months from now knowing I'll be home for them," rather than in jail.

Despite this knowledge, neither he nor Bob sought help at a place like the Sexual Disorders Clinic at Baltimore's Johns Hopkins University, where both of them now receive treatment for their urges under a court mandate. In individual and group counseling, they learn about the sources and triggers behind their urges, and develop tools to defuse those urges when they arise. Now, when Bob sees an underage girl, "I look away and say, 'I don't want that, no, go away.' I make myself feel the ugliness of the whole thing and it makes me feel bad.”

But Bob and Jimmy’s therapy isn’t just about helping them feel “bad” about their urges. Part of it is aimed at making them feel these urges less, through a treatment known as “chemical castration,” in the form of a drug called Depo-Lupron.

Chemical castration doesn’t resemble surgical castration at all. It’s a monthly injection of a testosterone-lowering drug, in this case Depo-Lupron (leuprolide), which is used to treat prostate cancer, but can also lower the intensity of sexual urges. Jimmy, a debt collector, pays up to several hundred dollars a month for his 7.5mg injections. On the drug, he says, life is better. He has a new fiancée, and describes his sex life as “good—that of a normal man.” He's no longer overwhelmed with the urge to flash strangers. "Life is more carefree," he says. "I can plan for events five or six months from now knowing I'll be home for them," rather than in jail. “If I wasn’t on [the drug], I wouldn’t be on the streets. I’d be locked up somewhere because I know I’d reoffend.”

Bob’s experience has been similar. He still has a sex drive, but it’s no longer out of his control. When he sees an adult woman, “I can become aroused, but it takes a little bit more effort—it’s not automatic.” The biggest drawback for him is the expense. “It costs a lot of money. With charges like this, it’s hard to get a decent job.”

The standard monthly dose of Depo-Lupron is $700 to $800, says a Sexual Disorders Clinic staffer, and insurers often won't cover the cost. Still, Jimmy says he'd rather work a day's overtime to pay for it than go back to jail. Also, the drug can decrease bone density. Jimmy, who's been on it for more than a year, says he broke his arm in December when he fell backward doing some plumbing, though he doesn't know if the drug was to blame. He'd need to do a bone-density scan to determine that, but that costs money, too. The drug also gives him hot flashes, he says. "It just feels like someone lit a torch inside you."

Still, he intends to keep taking Depo-Lupron for as long as it takes. “Until I feel I can come off of it safely,” he says. Residents of Maryland, both he and Bob are getting their Lupron treatments voluntarily. But some states mandate the injections—last year, Louisiana Governor Bobby Jindal authorized judges in his state to order chemical castration of convicted rapists upon their release from prison. And even as the Council of Europe is demanding that the Czech Republic stop surgically castrating violent sex offenders, chemical castration is gaining traction—Poland and Spain have both taken steps toward using the procedure.

"There is a huge body of scientific data in humans and animals documenting that, when testosterone is lowered, there's a dramatic decrease in sexual drive and in sexually motivated behaviors," says Dr. Fred Berlin, the founder of Hopkins' Sexual Disorders Clinic, where a staffer says that, of more than 100 patients, about 64 are on Depo-Lupron.

Some offenders still won't touch the stuff. In Atlanta, Roy Martin, 52, did prison time plus a supervised release for a 2002 conviction of possessing child porn. He now runs Roy Martin Ministries, a resource for recovering sex offenders. But he says that, were he still doing time, he wouldn't take a shorter sentence in return for agreeing to chemical castration. "It was bad enough that I did illegal drugs," he says, referring to a former crack habit he says he kicked with God's help, which he also credits with keeping him away from his old flashing and child-porn habits. "Why would I turn around and introduce another foreign substance into my body?"

Frank Zimring, a law professor at University of California at Berkeley and an expert on sex crimes, also has qualms. He says the idea that all sex offenders repeat their crimes is a “folk belief,” and that recidivist rates are much lower than widely believed. He cites a Department of Justice study that tracked nearly 10,000 sex offenders—more than 4,000 of them convicted of child molesting—for three years after their 1994 release; the re-arrest rate for another sex crime was only 5.3 percent.

Whatever its merits, chemical castration is a far less invasive option than what some sex offenders get in the Lone Star State. Texas is the only US state that authorizes only surgical castration for sex offenders: the physical removal of the testes. The procedure requires the consent of the offender, but even offering surgical castration is ethically suspect, say critics, who contend that the option is held out, unfairly, in exchange for reduced prison sentences—a cruel decision to force someone to make. "Castration sounds terrible," says Zimring, "but spending the rest of your life locked up also sounds terrible, and the question is the choice of evils."

Also, experts say, both types of castration will only work for sex offenders motivated by sexual desire rather than anger and aggression. "If you have people who aren't primarily motivated by sexual arousal, you have to layer interventions to maintain safety," says Maia Christopher, executive director of the Association for the Treatment of Sexual Abusers.

And guess who else doesn't have much patience with chemical castration as an alternative to lock-up? Certain victims' rights groups. "If they want to castrate them, that's fine," says Debbie Savoie, vice president of the Massachusetts group Community Voices. "The main issue," she says, "is they're not locking them up long enough."

Dr. Berlin says he can understand that hard-line point of view. "I discipline myself never to lose track of the fact that people can be innocent victims," he says. But after working closely with hundreds of sex offenders over the years, he sees them differently than does society at-large—as human beings with a vexing addiction, akin to alcoholism, rather than as monsters. "The best thing we could do would be to encourage these people to [seek treatment] before, rather than after, the fact. But we've demonized them. I'm sure there's a 17-year-old boy out there who realizes he's attracted to eight-year-olds but he's terrified to come forward."

Could that have once been the case with Michael Bizanowicz, now serving two life terms for the 2004 rape and murder of Woburn, Massachusetts, resident Joanne Presti and the murder of Presti's 12-year-old daughter, Alyssa? Presti's mother, Annette, who has since become an activist for stronger sex-offender laws in Massachusetts, doesn't much care. "At his trial," she says of Bizanowicz, "there were a lot of people with signs that said, 'Castrate.’ I thought about that a little and said, 'You know, maybe that's the answer—if it's something they can't control.'"

How would she feel if Bizanowicz got a shorter term in return for agreeing to be castrated? "I'd be angry," she says. "I really don't give a damn about him being castrated or not." Then, as though directly to Bizanowicz, she adds: "You just stay in jail."

*Some of the sex offenders’ names have been changed.

Tim Murphy has contributed to the New York Times, New York, Out, The Advocate and Poz. He lives in New York City.