CNA Explains: What is chemical castration and can it reduce sex crimes?

The Hastings Center for Bioethics in the US said that testosterone levels have been found to correlate with the risk of both committing violent crimes and reoffending.

Some research has suggested that chemical castration may reduce reoffending. British Justice Secretary Shabana Mahmood cited studies showing that chemical castration can lead to a 60 per cent reduction in reoffending.

However, individual findings suggesting a benefit do not mean the broader evidence is conclusive.

Mr Shanmugam has pointed out that the evidence on whether such measures are effective in bringing down crime rates remains inconclusive.

Similarly, Paul Cheong, senior lecturer at the Singapore University of Social Sciences who has taught criminal law, procedure and evidence, said that there is still no conclusive evidence that lowering testosterone levels reduces sexual offending or the likelihood of reoffending among convicted sex offenders.

Lowering testosterone may reduce sexual urges, but not all sexual offending is driven primarily by such urges.

Some critics have also questioned the ethics of mandatory chemical castration, given that the drugs can have side effects including depression, heart disease, weakened bones and reduced muscle mass.

There is also the possibility that sexual urges may increase again after treatment stops.

Psychological interventions may therefore be needed to address other motivations for offending.

Ms Mahmood, Britain’s Justice Secretary, said after the release of an independent sentencing review: “It is vital that this approach is taken alongside psychological interventions that target other causes of offending, like asserting power and control.”

The review highlighted that chemical castration would not be relevant for some sex offenders, such as rapists driven by power and control rather than sexual preoccupation, she added.