By Jenny Hope Last updated at 2:32 AM on 05th May 2009
A male contraceptive jab tested by scientists has proved to be as good as the Pill in preventing pregnancies.
However, findings from previous surveys have repeatedly suggested one stumbling block will be whether women would sufficiently trust men to make reliable use of hormonal contraception. In the latest study of more than 1,000 men, just over one in 100 conceived a child, similar figures to the 1 or 2 per cent of women who become pregnant while taking oral contraception.
The testosterone injection, which could be on the market in five years, was tested on a group of healthy fertile men aged 20 to 45, each of whom had fathered at least one child in the previous two years. Female partners were aged between 18 and 38 and had no reproductive problems.
Lead researcher Dr Yi-Qun Gu said: 'For couples who cannot, or prefer not to use only female-oriented contraception, options have been limited to vasectomy, condom and withdrawal. 'Our study shows a male hormonal contraceptive regimen may be a potential, novel and workable alternative.'
Similar findings of high effectiveness and complete reversibility have been made in recent years from trials using various forms of a male Pill to temporarily halt sperm production. The most popularly tested version contains the hormone progestogen, which can switch off the body's chemical signals that trigger the formation and maturation of sperm. This also leads to a lowering of natural testosterone output.
In order to counteract this a small amount of testosterone is given regularly, in this case by injection although it may be given via implants. In the latest trial on a jab, the men were given monthly 500 milligram injections of testosterone undecanoate in tea seed oil over a period of two and a half years. The men's fertility returned to normal in all but two participants after the treatment was stopped.
Testosterone injections lead to a reduction in levels of two regulatory brain chemicals, follicle-stimulating hormone and luteinising hormone. This in turn disrupts sperm production, but the effect is reversible. Sperm counts return to normal four to six months after the injections are halted.
Results from the Chinese trial, the largest effectiveness study of a testosterone-based male contraceptive ever undertaken, will appear in the June issue of the Journal of Clinical Endocrinology and Metabolism. The study, which was backed by the World Health Organisation, used buttock injections, alternating sides with each jab.
There were no serious side effects caused by the testosterone injections, although severe acne affected some volunteers. However, almost one third of 1,045 men enrolled in the trial did not complete it and no reason was provided for this. Dr Gu, from the National Research for Family Planning in Beijing, stressed investigation was needed into possible long-term effects.
He said: ' Despite the present encouraging results, the long-term safety of this hormonal male contraceptive regimen requires more extensive testing with a focus on cardiovascular, prostate and behavioural safety.'
A male contraceptive jab tested by scientists has proved to be as good as the Pill in preventing pregnancies.
The injection, which temporarily halts sperm production, was found to be 'highly effective' during trials. It is hoped the research could pave the way for both men and women to share equal responsibility for contraception. Sperm race: The testosterone injection works by reducing levels of two regulatory brain chemicals, which then disrupt sperm production
However, findings from previous surveys have repeatedly suggested one stumbling block will be whether women would sufficiently trust men to make reliable use of hormonal contraception. In the latest study of more than 1,000 men, just over one in 100 conceived a child, similar figures to the 1 or 2 per cent of women who become pregnant while taking oral contraception.
The testosterone injection, which could be on the market in five years, was tested on a group of healthy fertile men aged 20 to 45, each of whom had fathered at least one child in the previous two years. Female partners were aged between 18 and 38 and had no reproductive problems.
Lead researcher Dr Yi-Qun Gu said: 'For couples who cannot, or prefer not to use only female-oriented contraception, options have been limited to vasectomy, condom and withdrawal. 'Our study shows a male hormonal contraceptive regimen may be a potential, novel and workable alternative.'
Similar findings of high effectiveness and complete reversibility have been made in recent years from trials using various forms of a male Pill to temporarily halt sperm production. The most popularly tested version contains the hormone progestogen, which can switch off the body's chemical signals that trigger the formation and maturation of sperm. This also leads to a lowering of natural testosterone output.
In order to counteract this a small amount of testosterone is given regularly, in this case by injection although it may be given via implants. In the latest trial on a jab, the men were given monthly 500 milligram injections of testosterone undecanoate in tea seed oil over a period of two and a half years. The men's fertility returned to normal in all but two participants after the treatment was stopped.
Testosterone injections lead to a reduction in levels of two regulatory brain chemicals, follicle-stimulating hormone and luteinising hormone. This in turn disrupts sperm production, but the effect is reversible. Sperm counts return to normal four to six months after the injections are halted.
Results from the Chinese trial, the largest effectiveness study of a testosterone-based male contraceptive ever undertaken, will appear in the June issue of the Journal of Clinical Endocrinology and Metabolism. The study, which was backed by the World Health Organisation, used buttock injections, alternating sides with each jab.
There were no serious side effects caused by the testosterone injections, although severe acne affected some volunteers. However, almost one third of 1,045 men enrolled in the trial did not complete it and no reason was provided for this. Dr Gu, from the National Research for Family Planning in Beijing, stressed investigation was needed into possible long-term effects.
He said: ' Despite the present encouraging results, the long-term safety of this hormonal male contraceptive regimen requires more extensive testing with a focus on cardiovascular, prostate and behavioural safety.'
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