Surgical castration of sex offenders went out about 100 years ago, but it has been a dream of many doctors, police and prison officers - not to mention home secretaries - to find a magic pill that would stop paedophiles re-offending, particularly because some of them beg for help in controlling their sexual urges.

The Home Secretary, John Reid said yesterday that he is willing to take some tentative steps down the chemical road for those paedophiles who want it. In this he is falling into line with several US states (though some have compulsory treatment for re-offenders) and a few European countries including France, Sweden and Germany.

But the choice of treatment is difficult. Side effects are a problem with hormonal drugs, including, sometimes, the irreversible growth of breasts. Reid spoke in the vaguest of terms, but mentioned both "hormonal medication" and "one of the newer antidepressant drugs" - the SSRIs (selective serotonin reuptake inhibitors), which include Prozac and Seroxat.

The millions taking Prozac for depression - and, for that matter, the manufacturers - may not appreciate any glib link to chemical castration. What used to be known as the world's favourite happy pill does not end your sex life. But a reduced interest in sex is one of the recognised side effects and the Home Office says that "early evidence of greater control of deviant urges is encouraging". The department adds that drug treatment has to be coupled to psychological therapy.

In the US, the hormonal drug Depo-Provera is often used. This is injected progesterone, used worldwide as a long-term female contraceptive, which also inhibits testosterone production in men. But nobody believes drugs are a magic bullet. Sex offending is usually about power, violence and humiliation - not libido.