It could also ease the burden on the 225 million women in developing countries, who the World Health Organisation says have an unmet need for contraception. Yet so far only a US non-profit has taken up development of the technology abroad. For Sujoy Guha, the 76-year-old biomedical engineer who invented the product, the challenge now is to find a company who wants to sell it – even though male contraception is an area Big Pharma has so far shown little interest in. "The fact that the big companies are run by white, middle-aged males who have the same feeling – that they would never do it – plays a major role," said Herjan Coelingh Bennink, a gynaecology professor who helped develop the contraceptives Implanon and Cerazette as head of research and development in women's health for Organon International from 1987 to 2000. "If those companies were run by women, it would be totally different." Guha's technique for impairing male fertility relies on a polymer gel that's injected into the sperm-carrying tubes in the scrotum. The gel, which has the consistency of melted chocolate, carries a positive charge that acts as a buffer on negatively charged sperm, damaging their heads and tails, and rendering them infertile. The treatment, known as reversible inhibition of sperm under guidanc (RISUG) is reversed with a second shot that breaks down the gel, allowing sperm to reach the penis normally.

The expected launch of RISUG over the next two years will contribute to the Indian contraceptive market's 17 per cent growth through to 2021, according to a report last year from Pharmaion Consultants, based near Delhi. The procedure is 98 per cent effective at preventing pregnancy – about the same as condoms if they are used every time – and has no major side effects, according to R. S. Sharma, head of reproductive biology and maternal health at the Indian Council of Medical Research. About 540 men have received it in India, where it continues to prevent pregnancies in their partners 13 years after treatment, he said. A submission to regulators this year will seek approval for RISUG as a permanent method of birth control. That will be appended with clinical data supporting reversibility, Sharma said. India has more married women with an unmet need for family planning than any other country, and social stigma and a lack of privacy in shops has kept condom use to less than 6 per cent. Globally, men tend to take a back seat in matters of contraception. Almost 60 per cent of women in spousal relationships used the contraceptive pill or some other form of modern contraception worldwide in 2015, according to a United Nations report. In contrast, 8 per cent relied on their male partner using a condom. A new option for male birth control could garner as much as half the female contraceptives market, according to research by Organon in the 1990s, when the Dutch drugmaker partnered with Germany's Schering on the last major effort to develop a male birth-control pill. Demand would come from couples in long-term relationships looking to share family-planning responsibilities and single men looking for an alternative to condoms to prevent an unintended pregnancy from casual sex, Coelingh Bennink said.

Still, there were questions at Organon about whether it would be worthwhile financially to develop a new entrant in the low-margin contraceptives market, and the project was eventually shelved, he said. Efforts on a hormone-based male contraceptive continued in 2008 in a study co-funded by the Bill & Melinda Gates Foundation and UN agencies that was published in October. While the injected regimen's efficacy was "relatively good" compared to other methods, the study was terminated early after a safety review. The authors noted a "relatively high" frequency of mild to moderate mood disorders, sparking a media uproar over perceived double standards in the development of contraceptives because the side effects seemed similar to those women experience on the pill. Male contraception isn't an area of active research for Pfizer and Merck either, representatives said. Both companies sell products for female fertility control. Side effects aside, it would take about $US100 million and 10 years to bring a hormone-based male birth control pill to market – a low-priority undertaking for pharmaceutical executives, Coelingh Bennink said. That's now the dilemma Indian inventor Guha faces.

"In doing anything abroad, quite substantial money is required, and that can only come from the pharmaceutical industry," Guha said, surrounded by dusty stacks of paper, books and prototype inventions that bury every surface in his office at the Indian Institute of Technology in Kharagpur, about 130 kilometres west of Kolkata. In the face of disinterest from the pharmaceutical industry, Guha licensed the technology to the Parsemus Foundation, a US-based non-profit, to help establish a market for it outside India. Parsemus is working on its own version, called Vasalgel, that it plans to manufacture and distribute at near cost – or potentially $US10 to $US20 per person in low- and middle-income countries – and $US400 to $US600 per person in wealthier markets, said Elaine Lissner, the foundation's founder. The foundation, based in Berkeley, California, is seeking donations to fund costly human trials starting next year after a study in 16 rhesus monkeys published last month showed Vasalgel was successful in preventing conception while the primates fraternised with females for 5 to 24 months. Guha meantime has registered a start-up in India called IcubedG Ideas through which he is pushing ahead with introducing the technology in his home country.

Kinkar Ari, a 39-year-old day labourer from a nearby village, said that when he and his wife Aloka decided they didn't want more children, they had a choice between tubal ligation for her or vasectomy for him, but neither could afford the time off to recuperate from the surgery. When a public health worker told the couple about Guha's promising alternative, Ari decided to enrol in the study. The injection took 15 minutes with some local anaesthesia, and after half an hour of observation at the clinic, he said he was able to walk the 2.5 kilometres home. Two days later, he was back at work. Ari was so enthused by the procedure, he convinced two other couples to have it done, he said. Stories like that encourage Guha to persist with the project, even though patents on his invention have long since expired and he won't see any personal financial gain even if it takes off worldwide. "Why should the burden be borne by the female only?" he said. "There has to be an equal partnership." With Jared Hopkins and Johannes Koch