Gov. Kay Ivey of Alabama has signed a so-called chemical castration measure into law, her office announced Monday, leaving the state poised to set a stringent new parole condition for certain sex offenders.

Supporters of the law contend that it will enhance public safety and reduce the risk of convicted sex offenders committing similar crimes once they are released from prison. But critics of the law, which will take effect in September, think it may prove unconstitutional.

Here is a guide to the procedure, which is used in a handful of states and in some places outside of the country.

What is chemical castration?

Chemical castration involves using a drug to reduce testosterone levels and affect the sex drive. U.S. doctors have been using medroxyprogesterone acetate — the protocol expected to be used in Alabama — to treat sex offenders for more than 50 years.

The procedure does not cause sterilization and is not permanent.

What will Alabama require?

The new law requires people who were convicted of certain sex offenses, including rape, sodomy or incest, involving victims younger than 13 to receive chemical castration as a term of parole.

Under the measure, the Alabama Department of Public Health will oversee the procedures, which parolees will pay for, and people will “continue receiving treatment until the court determines the treatment is no longer necessary.” (The law has a limited exception for indigent people who cannot afford the procedure.)

A person who “intentionally” ends treatment will have committed a felony under the law. It was not immediately clear how many people will be affected by the law.

Do other states have castration laws?

Yes. A 1996 California law — the first of its kind in the United States — set out requirements similar to the ones that are planned in Alabama. Other states that have castration provisions in their laws include Florida, Louisiana and Wisconsin.

Castration procedures are also used overseas, and in 2016 Indonesia amended its laws to allow chemical castration.

Does it work?

In a 2005 review of medical literature in the Journal of the American Academy of Psychiatry and the Law, researchers said that chemical castration “reduced testosterone levels and affected sexual deviance.” But they added a note of caution: “These studies used self‐report to measure decreases in deviant sexual drive, fantasies and behavior — a methodology with questionable reliability.”

A report in the Journal of Korean Medical Science in 2013 said that chemical castration “results in very low levels of recidivism despite the strong psychological factors that contribute to sexual offending.”

Researchers in the United States and abroad have also found substantially lower recidivism rates among people who had surgical castration procedures, compared to people who were released from custody without any such treatments.

What are the ethical concerns?

Some critics contend that chemical castration laws are improperly coercive to inmates, who might be forced to choose between staying in prison and taking the drug. Doctors and medical ethicists have also expressed concerns about side effects and whether prisoners receive enough information to make appropriate, informed decisions.

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