Scientists believe they are one step closer to developing an effective male contraceptive jab after successfully carrying out the largest feasibility study to date.

Researchers at the National Research for Family Planning in Beijing injected 1,000 healthy, fertile male patients with a testosterone-based jab over a two-year period and found only 1 per cent went on to father a child. The men were all aged between 20 and 45 and had fathered at least one child in the two years before the testing began. They were also all involved with healthy female partners between the ages of 18 and 38 who had no reproductive problems of their own.

The trial was the largest effectiveness study of a testosterone-based male contraceptive ever undertaken. At the end of the two-year period only one in 100 men had fathered a child. No contraception is 100 per cent effective – 1 to 2 per cent of women still become pregnant while they are on the Pill – but the jab's success rate puts it on a par with the effectiveness of the female Pill or injections.

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Dr Yi-Qun Gu, one of the researchers involved in the testing, 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."

When the contraceptive Pill was introduced in the 1960s it revolutionised sex lives but also placed the onus of reproductive responsibility on women. Scientists have been looking to try to find a suitable alternative for men but have struggled to control male hormones with the same level of efficiency. Previous attempts to develop an effective and convenient male contraceptive have encountered problems over reliability and side-effects, such as mood swings and a lowered sex drive.

Like the female Pill, most testing for a male pill or injection has centred on using hormones to stop the production of key elements of the reproductive process. For the testing in China, a country which has invested heavily in reproductive technology because of its overpopulation problems, the men were given 500mg of testosterone undecanoate (TU) in tea seed oil. The injections resulted in a reduction of two regulatory brain chemicals, follicle-stimulating hormone (FSH) and luteinising hormone (LH) which in turn disrupted sperm production.

The scientists claim that there were none of the usual side-effects and say the process is reversible. Six months after coming off the injections, the men's sperm count had returned to healthy levels. Dr Gu said further testing would be needed to check how safe testosterone injections are.

Family planning campaigners have welcomed the news and said they hoped an injection would result in men taking a greater level of responsibility over contraception.