Sex offenders are to be offered drug treatment under new plans announced by the Home Office. What would such a programme involve?
Eunuchs can still perform sexually despite being castrated
The list of potential side-effects might put anyone off, but a libido can effectively be reduced by a number of drugs.
These can either be administered through injection or tablet, but both have the same effect: cutting the amount of testosterone pumped around the body and thus curbing a man's sex drive.
The first is a pill taken daily known as cyproterone acetate - or Androcur. This is a drug that is usually prescribed to women with major hormone imbalances resulting in the growth of body hair or severe acne.
The particular disadvantage of this form of treatment may be the fact that it relies on the patient to take the medication each day - although given that the scheme will be voluntary in any case this may not present a grave problem.
The second option is a monthly injection, usually administered into the buttock. This is the drug leuproreline, which is used in the treatment of prostate cancer.
The principle issue with leuproreline, experts say, is that in the four to six weeks following the start of treatment, testosterone levels rise before falling.
But once this period is past, sexual desire will drop dramatically.
A patient will still be capable of having sex - many eunuchs, who have been castrated, are still able to perform sexually.
But arousal will be significantly more difficult.
It would in most circumstances require the man to either come up with an extreme sexual fantasy or to watch some extreme pornography.
"Anybody who wanted to overcome the effects of these drugs, ultimately, probably could," said Professor Ashley Grossman, an endocrinologist at the William Harvey Research Institute.
"They help people who want to help themselves, so in that respect it's probably makes sense for it to be voluntary."
The side-effects of the drugs are also likely to be taken into account by anyone considering joining the programme.
In addition to losing his sexual interest, a man taking them is likely to become more feminised.
He may lose his body hair, and gain weight around his middle. He may also experience hot flushes like those experienced by women during the hormonal changes of the menopause, lose muscle density, become anaemic and irritable.
In the long-term, he will also run the risk of osteoporosis as his bones get thinner.
"There are definitely adverse affects," says Dr Pierre Bouloux of the Royal Free Hospital.
He estimates the cost of the treatment to be in the region of £2,000 - £3,000 per year.
Other estimates suggest the cost may be even lower - perhaps as little as several hundred pounds.
Treatment which focuses on reducing libido is unlikely to be offered in isolation. Alongside counselling, many sex offenders are prescribed anti-depressants.