Child sex offenders incarcerated in a Nottinghamshire prison are undergoing chemical castration, after volunteering for the controversial treatment.

According to the Daily Mirror, 100 paedophiles offered to undergo the scheme at HMP Whatton, operated in connection with the Ministry of Justice and Department of Health.

Forensic psychiatrist Professor Donald Grubin, who is running the pilot scheme at the prison, said inmates undergoing the treatment were doing so in order to "control their arousal and reduce their risk".

"The primary indications are where men have high levels of sexual arousal that they find difficult to control, or have intense sexual ruminations or fantasies that they find hard to resist," he told Huffington Post UK.

Professor Grubin said he had had around 100 patients referred to him over the last three years, but not all of them underwent the controversial treatment.

"There are two types of medication that can be prescribed: anti-androgens (sometimes referred to as 'chemical castration'), and selective serotonin reuptake inhibitors (drugs like Prozac).

"The former can remove all sexual desire, but in some cases men can still maintain sexual relationships; the latter reduce the intensity of fantasies and urges, but do not remove sexual drive. In both cases psychological treatment should be provided alongside the medication."

HMP Whatton is a category C prison, which means that though the prisoners are considered dangerous to society, they are also thought to be unlikely to escape. It is the lowest security prison before an open facility.

Additionally all inmates housed at HMP Whatton are sex offenders that have signed up to the government's Sex Offender Treatment, which uses a number of educational schemes to rehabilitate prisoners.

However chemical castration is not without its risks. One of the psychological side effects of the anti-androgens, is that men can struggle to come to terms with being completely asexual.

For this reason Professor Grubin stressed that psychological treatment needs to be prescribed alongside the medication especially as depressed mood is another of the potential side-effects. Physical side effects of the anti-androgens can also be severe, with the drugs causing thinning of the bones, an increased risk of cardiovascular disease, fatigue, and breast growth.

Chemical castration is likely to be controversial method of rehabilitating sex offenders, especially as it is funded by the public purse.

Frances Crook of the Howard League for penal reform said that chemical castration will not necessarily reduce the risk to the public:

"Sex offending is often not about sex at all, but about violence and domination. The drugs used will not affect those attitudes. Some men may inflict other types of deviant behaviour on victims if they are unable to perform sexually due to the drugs."

"'Feminising' sex offenders may make it more difficult for these individuals to reintegrate into society, which in turn makes their reoffending more likely.

Wartime codebreaker Alan Turing was given the choice of jail or chemical castration after being convicted of homosexuality in the 1950s. After taking the drugs he killed himself. We would be concerned if similar choices were offered to individuals in the future."

However Professor Grubin said that because medication is being prescribed to reduce sex drive, rather than for 'social control' offenders are able to stop taking the medication whenever they want.

"The benefits of the pilot are that sex offenders for whom medication may be of benefit can get it, improving their quality of life and reducing their risk." he added.

"There is no real downfall, provided it is prescribed appropriately. The difficulty is in finding local psychiatrists willing to assess and prescribe, which can be hard work."

A Ministry of Justice spokesperson said:

"We continue to support the use of pharmaceutical interventions for some high risk sex offenders given the evidence that medication can be useful in reducing risk for some perpetrators of these crimes.