Indonesia will start chemically castrating convicted paedophiles in a bid to fight child sex abuse, the country's attorney-general said.

The move comes following a string of high-profile child sex crimes. These include the rape last year of a six-year-old pupil at the Jakarta Intercultural School by a group of janitors, and the rape and murder of a schoolgirl in Jakarta earlier this month.

"We are very concerned about child molestation abuse cases. This phenomenon has reached extraordinary levels," Attorney-General H.M. Prasetyo told reporters after a Cabinet meeting late on Tuesday (Oct 20).

We take a look at the punishment, and the countries that use it.

What is it?

Chemical castration does not involve the mutilation of the offender's genitals. Instead, they are injected with hormones that reduce testosterone levels, the male hormone responsible for libido.

One such hormone is medroxyprogesterone acetate (MPA), which is primarily used as a female contraceptive.

Continued administration of the hormone at regular intervals keep the offender's testosterone levels low, reducing sexual urges.

The effects of MPA injections are completely reversible, but can cause side-effects like diabetes, hypertension, and in the long run, brittle bones.

Where else is it practised?

South Korea

South Korea became the first country in Asia to legalise the punishment in 2011. A Bill passed in July that year allows for chemical castration for convicted child molesters aged over 19 years, who are at risk of repeating their crimes against those below 16.

Since then, two men have been chemically castrated. Park, then 45, became the first in 2012 when he was sentenced to receive an injection every three months for three years.

He was released from prison in July that year after serving a 10-year sentence for attempting to rape a 10-year-old girl. He had previously served jail terms in 1984, 1991 and 1998 for sexually attacking girls under the age of 16.

A man surnamed Pyo, then 31, in 2013 became the second man to be given the punishment for having sex with five teenagers whom he met through a smartphone chat service. He also threatened to circulate online video footage of them engaged in sexual acts, and raped them after threatening them with weapons.

United Kingdom

Renowned World War II codebreaker Alan Turing, whose life was brought to the big screen in last year's Oscar-winning movie The Imitation Game, was picked up by police in the United Kingdom and prosecuted for homosexuality in 1952, when it was a crime.

Subjected to chemical castration, he killed himself at the age of 41. Turing was officially pardoned by Queen Elizabeth II in 2013.

More recently, paedophiles in UK prisons have volunteered to undergo chemical castration in an effort to prevent themselves from reoffending. Twenty-five volunteered for the punishment in 2014, the UK's Ministry of Justice said.

United States

At least nine US states, including California, Florida, Oregon, Texas and Washington use chemical castration.

Russia

A Bill proposing that chemical castration be made mandatory for paedophiles who commit crimes like raping children under the age of 14 was submitted to the State Duma on Tuesday (Oct 20).

The law in the country currently allows for the punishment for convicted paedophiles if it is recommended by a panel of doctors.

Poland

A law that forces men who rape children and immediate family members to undergo chemical castration came into effect in June 2010. Prisoners are forced to take the hormones upon their release, but courts have to consider psychiatrists' opinions before ordering the punishment.

Does it work?

It is not clear that a programme of the hormone MPA will definitely reduce sexual reoffending rates, The Straits Times' Andy Ho wrote in 2013. Studies looking at sexual reoffending rates are methodologically flawed and too small in size. "In sum, MPA is no insurance against sexual recidivism," he said.

However, an expert told the CNN in 2012 that the punishment works. Newcastle University professor of forensic psychiatry Don Grubin said: "It's clear the drugs work. If you look at men, they do reduce sex drive drastically. They do reduce re-offending in the men."

Sources: The Straits Times archive, The Moscow Times, International Business Times, BBC, CNN