Drugs that help control the libidos of people who have committed sexual offences could be rolled out for thousands of male prisoners in England and Wales from December 2028, an expert has said.
Prof Belinda Winder, who has evaluated the use of sex drive-suppressing medication in prisons, said about one in four sex offenders – equating to 3,750 current prisoners – would be considered for the treatment.
Government sources have told the Guardian that Andy Burnham’s administration is keen to expand the voluntary use of sex drive-suppressing drugs amid a scramble to ease the prison overcrowding crisis.
However, ministers are re-evaluating whether to press ahead with Shabana Mahmood’s pledge to explore mandatory chemical castration of serious sex offenders, such as paedophiles and rapists.
About 15,000 prisoners in England and Wales are serving a sentence for a sexual offence, and more than 850 men a month are arrested on suspicion of online child sexual abuse offences.
A pilot programme, the medication to manage problematic sexual arousal treatment pathway (MMPSA), will be expanded from 10 to 20 prisons in November. The next phase will extend from south-west England into two additional NHS regions, the north-west and north-east.
It is meant to target sex offenders who experience intrusive, persistent and intense sexual thoughts, persistent arousal, and unhealthy sexual urges and sexual behaviours. Prisoners on the trial can be offered drugs including selective serotonin reuptake inhibitors (SSRIs), such as sertraline, which helps to limit invasive sexual thoughts, and anti-androgens, which reduce the production of testosterone and limit libido. In some cases, it reduces testosterone to pre-pubescent levels.
Winder said officials could be ready to launch the drugs in prisons and probation services across England and Wales within 28 months if the pilot continued to progress.
“They [the Ministry of Justice] could be ready in December 2028 to roll the programme out if the interim findings look useful,” she said.
Those on the scheme would have to receive clinical support if they were to commit to taking the drugs and not reoffend, Winder said. “I am optimistic that a properly resourced, voluntary national MMPSA pathway could ultimately be developed … A good national service needs appropriately trained clinicians, clear referral routes, appropriate psychological support alongside medication,” she said.
Last year Mahmood, the then justice secretary, told MPs she was exploring a national rollout of voluntary chemical castration for sex offenders and whether it could be made mandatory.
Two experts have told the Guardian that the plan will not work. Winder, a co-chief investigator of a Prozac clinical trial with sex offenders, said she had significant concerns.
“A mandatory approach would require screening a very large prison population to identify the much smaller group for whom treatment might actually be appropriate,” she said. “It would have substantial clinical and resource implications.”
There were also concerns that if it was mandatory, there could be a breakdown of trust with offenders and it could be open to abuse, she said.
“Trying to impose and monitor daily medication among people who do not necessarily want to take it could be extremely inefficient. It could also introduce a range of consequences that we simply do not yet understand, including effects on trust, disclosure, engagement and the therapeutic relationship.”
She rejected characterising the drugs as a form of “chemical castration”. “People say that because some people like the idea of castrating people who commit sexual offences,” she said. “But these drugs are not permanent, unlike castration, and must be taken consistently to work.”
Burnham announced earlier this month that prisoners convicted of rape, grooming and serious child sexual offences would be excluded from the early release scheme that is due to begin in October. Other sex offenders serving sentences of less than four years will still be eligible to leave prison early.
There are comparatively low reoffending rates among sexual offenders compared with other cohorts. According to government data, 11.7% of sex offenders reoffended in 2023, compared with 53.9% of those with an index offence for theft.
Prison campaigners have urged caution before going ahead with a national programme. Critics have previously pointed out that long-term testosterone suppression can cause osteoporosis and cardiovascular disease. There is limited data because randomised controlled trials remain scarce.
Andrew Neilson, the director of campaigns at the Howard League for Penal Reform, said: “The history of prison-based treatment programmes in this area has proven troubled, which is both a reason for exploring alternatives but also a reason to exercise caution before expanding new approaches more widely. It’s also important that nobody is forced into these chemical interventions and that participation is truly voluntary.”
Mark Fairhurst, the national chair of the prison officers’ union the POA, said: “Anything that potentially protects the public is welcome but I would be cautious about the rollout until we are in receipt of evidence that proves success.”
A Ministry of Justice spokesperson said: “This government is determined to tackle the root causes of sex offending, which is why we’re working at pace to extend the existing pilot to a further two regions.”
Additional reporting by Faisa Mohamed
