If we could put ethical considerations about nonconsensual medical treatment aside, it still wouldn’t be clear whether this approach will have the desired effect on recidivism. Most research in the area puts sexual desire low on the list of reasons people assault children. The best predictor of sexual assault is not libido, research has shown, but “an early and persistent general propensity to act in an antisocial manner during childhood and adolescence.”

The physiological effects of androgen blockers are well established, because the drugs used in chemical castration are also commonly used in people with cancer, especially of the prostate, where testosterone can help tumors grow. In addition to lowering libido and causing sexual dysfunction, the sudden removal of androgenic hormones has been known to impair performance on visual-motor tasks and cause declines in bone density, increased rates of fractures, and depressive symptoms.

It has been well demonstrated that surgical castration, which has been practiced in various places for millennia, makes sex offenders either unwilling or simply unable to commit future offenses. The evidence on chemical castration is much less clear. In the same way that removing the hands of a bread thief could theoretically help prevent future crimes, rendering a person’s genitals less virile makes certain acts less feasible. But unlike other therapeutic approaches, chemical castration (or surgical castration, for that matter) does not address the antisocial instincts that often underlie such crimes.

Some ethicists argue that child offenders are diseased, and it is only humane to treat them—even sometimes without consent. This is predicated on the basic idea that assault is a result of an imbalance of hormones, whereby too much testosterone leads to rape. On the whole, however, sex offenders do not have higher levels of testosterone than the average male. A recent meta-analysis of research found “no evidence to suggest there is anything chemically wrong with sexual offenders.”

Assault is not a typical outlet for those who have strong libidos or think often about sex. The desire to take another person by force has long been known to be primarily about power and dominance. If chemical castration is indeed effective, the meta-analysis notes, “it is not because it is treating an abnormal medical condition, but rather because it is inhibiting sexual functioning in the same way it would for most humans.”

In psychiatry, there are some accepted uses for androgen-blocking medications. As the Johns Hopkins psychiatrist Fred Berlin has noted, in these cases drugs are used for “diminishing the intensity of the eroticized urges that energize unacceptable para-philic behaviors”—in other words, when a person is concerned about acting on urges they know to be wrong or illegal, and so seeks preventive help. Other people seek help when an all-consuming libido becomes a problem in daily life.