Chemical castration for sex offenders to be trialled in 20 prisons

The pilot for the voluntary chemical castration of sex offenders will be extended to 20 prisons in England, the justice secretary has said.

Shabana Mahmood said she would expand a small pilot in south-west England to two regions, after an independent sentencing review recommended it continue.

Mahmood is also exploring a national rollout of voluntary chemical castration for sex offenders, and whether it could be made mandatory. No timeline for this decision has been set.

Forensic psychiatry Prof Don Grubin said he did not think the government would "get the mandatory element of it off the ground" as to "simply make somebody take [the treatment] would be very unethical and...most doctors I know would be resistant to it".

Chemical castration, which is delivered through drugs taken alongside psychiatric work, is targeted at sex offenders who have compulsive and invasive thoughts about sex, or have problematic sexual preoccupations.

The approach has been used in some European countries. In Germany and Denmark, the use of chemical suppression has only been administered on a voluntary basis, while Poland introduced mandatory chemical suppression for some sex offenders.

The suggestion to continue the pilot in England and Wales was one of 48 recommendations set out by former Lord Chancellor David Gauke's Independent Sentencing Review, which was commissioned to look into the causes of the prison overcrowding crisis and to consider alternative punishments to custodial sentences.

Mahmood told the House of Commons on Thursday that she will go further and expand the pilot to build evidence and "make sure that we are using every tool at our disposal that can cut reoffending".

The government has not confirmed which regions or prisons will be part of the widened pilot scheme.

"I'm not squeamish about taking these further measures," she said. "I will make sure that that is what happens."

She also told the Commons she was "exploring whether mandating the approach is possible".

"It is vital that this approach is taken alongside psychological interventions that target other causes of offending, like asserting power and control," she added.

"For some, offending relates to power, but for another subset of offenders, the combination of chemical suppressants and psychological interventions, can, we believe, have a big and positive impact."

Gauke's report said sexual offences accounted for 21% of adults serving immediate custodial sentences at the end of March 2025.

The review made the recommendation to "build a comprehensive evidence base around the use of chemical suppression for sex offenders and explore options for continued funding of services in this area".

It cautioned that use of these medications "should never be used as a risk management tool or standalone rehabilitative offer, and it is only appropriate for a limited number of sex offenders".

Understanding how other jurisdictions have managed the "ethical and practical implications" is crucial as gaining "valid, informed consent" to a course of treatment is a key tenet of medical law in England and Wales, the review said.

Gauke told BBC Breakfast on Thursday the review was making "cautious recommendations" and there would be "caveats" to the continued scheme.

"It is not the answer for every sex offender - this is something we would see as a treatment essentially for reducing the risk of reoffending, rather than a punishment," he said.

"The review recommends exploring how the scheme operates on a voluntary basis rather than mandatory basis, that's the position of the review."

Prof Grubin said hormonal medications have "pretty serious side effects" and "somebody would have to really want to get their sex drive under control to agree to be on those drugs".

However, he said you could make it a condition of a parole licence, such as in California, where it is mandated for a second time sex offender when the victim is under 13.

He hoped the extension of the voluntary pilot would go ahead "because while we have had clinics running in the prisons for quite a while, we've always had difficulty getting it rolled out into the community".

"If this gives it a push, that would be great," he said.

Josh Babarinde, the Liberal Democrats' justice spokesperson, said "the data and evidence (about ongoing voluntary suppression medication pilots) must be made fully transparent so that the effectiveness of this intervention can be properly scrutinised".

The move to introduce stricter measures than Gauke's recommendation in this area comes as the government faces pushback from some opposition parties to accepting most of his other suggestions, including earlier release for some offenders.

Is chemical castration effective?

Chemical castration is delivered through two drugs. Selective serotonin reuptake inhibitors (SSRIs) limit invasive sexual thoughts, while anti-androgens reduce the production of testosterone and limit libido.

The drugs are taken alongside psychiatric work that targets other causes of sexual offending, such as a desire for power and control.

These medications have been delivered in some prisons through the Offender Personality Disorder Pathway, a national programme commissioned by the NHS and the HM Prison and Probation Service.

The scheme was first piloted in HMP Whatton in 2007 and later rolled out in six more prisons in 2016, Gauke's review said.

A 2022 pilot extended the programme to five prisons in south-west England.

Research on the impact of chemical castration - while limited - has shown considerable reductions in reoffending rates. One study followed ten offenders, none of whom reoffended after treatment.

Another study paired one group of sex offenders who had been chemically castrated with another who had not. Reoffending rates were 60% lower among the group who had been chemically castrated.

Prof Grubin said the intervention is "about doctors treating patients, rather than doctors doing a job for criminal justice agencies, but a side effect is that reoffending is likely to be reduced, because we know an important factor in sexual offending and sexual reoffending is sex drive".

Prof Grubin said the reoffending rate for people on the hormonal medication "is very, very low" because it is effective at reducing sexual drive.

However, he said that effectiveness is hard to demonstrate in reoffending studies because it takes years to see if it is having a long-term effect, and because no one will agree to randomise a high risk sex offender who does not take the medication with someone who does to compare.