Chemical castration is the colloquial term for two main approaches to working with sex offenders.

Anti-depressants or SSRIs are used to help reduce te frequency and intensity of sexual fantasies and obsessions and help an offender control their thoughts. Anti-libidinal drugs such as cCyproterone acetate (Androcur), are used to lower testosterone levels and as a result are also used to treat testicular cancer.

The reduction in testosterone levels can make sexual arousal less likely, meaning a patient may be less likely to act on fantasies or intrusive sexual and criminal thoughts.

READ MORE: Chemical castration of sex offenders re-examined

There is disagreement about whether these drugs can also play a part in reducing such fantasies in the first place.

These drugs have side effects including feminisation and gynomastia – enlargement of the breasts, an effect suffered by British computer pioneer Alan Turing who was notoriously forced to take them in a bid to “cure” him of homosexuality.

In Scotland, nobody can be forced to take them, an offender has to do so voluntarily.

This is not the case in countries such as Indonesia, Poland and South Korea where the courts can impose treatment, as well as several US states, including California, Florida and Oklahoma, where treatment can be mandatory after a second offence.

Coutntries, such as Sweden, Denmark, Canada and Australia use the treatment but it is voluntary as in the UK. Following the gang rape of a woman in Delhi in 2012 - which caused worldwide outrage - the Indian Government has also begun legislation to allow chemical castration and sentences of up to 30 years for rape.

READ MORE: Chemical castration of sex offenders re-examined

However, while the idea of forced chemical castration is often popular with the public there is considerable controversy about how effective it genuinely is, and the human rights implications of making someone take medication against their will.

Even proponents such as the late psychologist Dr Ludwig Lowenstein, while arguing that the child’s right to protection outweighed any rights for paedophiles, said the treatment needed constant supervision.

“Offenders have to keep taking the pills to lower their libido. Nor is it a total cure: paedophiles’ sexual behaviour is governed not only by hormones but also by fantasies so they will still be drawn to children,” he said.

But there is also a major lack of evidence on the effectiveness of chemical castration. In 2015 researchers said they could find only seven trials, all small and short and all over 20 years old.

Proof that such treatment reduces reoffending was “poor” and researchers expressed concern that evidence was so sparse given that in many countries offenders can be forced into treatment.

READ MORE: Chemical castration of sex offenders re-examined

There are many unanswered questions, about whether those who agree to such treatment are already those less likely to reoffend, or whether by destroying the ability to have normal sexual intercourse drugs could make some people more, not less likely to engage in deviant behaviour.

However it is difficult to imagine an ethical trial which would measure the effectiveness of rival methods of preventing sexual attacks.