It is a breakthrough many hope will herald a new era for modern relationships and transform sex lives across the world.
British couples are among hundreds worldwide trialling a pioneering form of contraception - designed specifically for men. If it's a success, and early results are good, it could be the first nonpermanent male contraceptive to become available since condoms were invented more than 400 years ago.
The treatment is a hormone-based gel, clear in colour and the consistency of hand sanitiser, that's applied to the shoulders every morning, where it is quickly absorbed by the skin. Within weeks, the user's sperm count plummets and - once levels are low enough - it can work as a couple's only form of birth control.
Experts say there are few, if any noticeable side effects, and they hope it will work as well as the Pill, which is 99 per cent effective when taken perfectly.
The landmark international trial is already under way, and the results could prove revolutionary. Now, two couples taking part have spoken exclusively to The Mail on Sunday about their experiences.
John Vandesquille, 30, has been using the gel since May last year.
John, from Manchester, who works in marketing, signed up for the trial after his partner, 28-year-old Alex Smith, was told she would be unable to continue taking the Pill due to it reacting with another medication she was prescribed.
Just a month in, tests showed that his sperm count had dropped. Doctors running the study reassured him that should he stop using the medication, it would recover completely. After two months, the couple were given the green light to use the gel as their sole method of contraception.
'I wasn't particularly worried,' John says. 'It's not the first time the gel had been tested - so it wasn't a complete jump into the unknown. The possible long-term effects on my fertility were more concerning - and it's still something at the back of my mind. But Alex and I are 80 to 90 per cent sure we don't want children in the future, so that's less of a worry for us. So far, I don't feel any different. And our sex life has carried on as normal, or maybe even better than normal. I'm not sure if that's to do with the gel itself - but our relationship has definitely improved.'
LOTS OF CHOICES... BUT THEY ARE ALL FOR WOMEN
For decades, it seems, women have shouldered much of the burden when it comes to contraception.
First made available on the NHS in 1961, the discovery of the Pill - now taken by more than three million British women - opened the floodgates for other methods of birth control. Today, there are patches, injections and implants offered to women to avoid pregnancy.
Hormonal contraceptives all contain a small amount of artificial hormones. These work to inhibit the body's natural production - stopping eggs from being released from the ovaries and making it more difficult for sperm to reach and fertilise an egg. Other types also change the lining of the womb to make it unlikely a fertilised egg will be implanted.
The story for men could not be more different. Aside from condoms, the only other option is permanent: a vasectomy, in which tubes that carry sperm are cut and tied, rendering the individual sterile. The need for alternatives is clear.
Thousands of women complain of side effects from the Pill, such as mood swings and headaches. Others long for a break from artificial hormones. Many started taking the contraception as teenage girls and, with more and more starting a family later in life, they continue doing so well into their 30s.
The popularity of apps such as Natural Cycles, which markets itself as hormone-free contraception, tracking body temperature to detect when a woman is fertile, or not, and therefore not at 'risk' of getting pregnant, shows there is demand for more choice. But the app has faced a backlash, with scores of women reporting unwanted pregnancies after using it - and experts urge caution.
Could the male contraceptive gel, known as NES/T, be the answer?
'In many couples, the woman struggles with contraception,' says consultant gynaecologist Dr Cheryl Fitzgerald, who is leading the trial at Saint Mary's Hospital, part of Manchester University NHS Foundation Trust. 'But at the moment the only alter native options for men are using condoms, or a vasectomy. It is envisaged that this gel would be used by couples in steady relationships. But, going forward, there may also be men in casual relationships who want to know they are not going to produce a pregnancy. At the moment, men don't have much control over that.'
I WON'T GET PREGNANT... I TRUST THE DOCTORS
Like many teenagers, Alex first went on the Pill when she was 16. The medical administrator from Manchester continued to use hormonal contraception without problems for more than a decade. But last year, she was told by her GP she would need to go on medication to treat repeated head aches - which would have inter fered with her contraception.
'We were feeling at a bit of a loss,' Alex says. 'The only contraception I could have gone on was the coil [a small metal or plastic implant that sits in the womb, stopping conception], which I didn't really like the idea of. And we weren't keen on just using condoms.'
It was then that her partner of five years, John, spotted an advert on Facebook looking for couples to try out the NES/T gel at St Mary's Hospital - one of two UK sites involved in the inter national trial, along with the University of Edinburgh.
Having been accepted on the trial, John rubs the gel into his shoulders every morning after showering. Within seconds, it disappears.
'I use one pump-worth on each shoulder,' he says. 'It only takes a minute to apply and is very easy to use.'
The gel can be applied anywhere on the body - it quickly enters the bloodstream via the skin - but the researchers advise using the shoulders for convenience.
Throughout the study, John will attend monthly hospital appointments, where doctors check his sperm count stays at the acceptable low level. A count under 15million is considered low, but it needs to be kept under one million to be an effective contraceptive. John will use the gel for a year as part of the trial, and will be monitored afterwards, to check that his sperm count returns to normal.
'Several decades of experience doing similar trials show that sperm count always does return to normal afterwards,' says Professor Richard Anderson, who is leading the trial at the University of Edinburgh. 'We are absolutely confident that this will be the case for this one.'
Alex admits she was initially worried about getting pregnant.
'There was a little voice in my head,' she says. 'But I put a lot of trust in the doctors and nurses running the study. I also began to realise that no contraception is 100 per cent effective. Every time we have sex we are taking a risk and I could become pregnant. So I was able to let it go, and now I don't even think about it.'
The couple, who met on a dating app and moved in together six months later, believe passionately that there should be more alter natives for men and hope the research could help address this unmet need.
'The fact that there are no male contraceptives except for condoms is not fair,' John says. 'It's not fair on women and it's not fair on men either.'
Alex adds: 'At the end of the day, it takes two people to conceive. So why is it just the woman who determines whether that happens or not?'
NO REDUCED LIBIDO... OR OTHER SIDE EFFECTS
The new gel has been designed to suppress sperm production with out affecting libido. It contains a combination of two hormones - segesterone acetate and testosterone.
Testosterone alone can lower sperm levels in men and reduce the chances of causing a pregnancy. But the high doses needed to do this can be dangerous. Men who take too much testosterone - for example bodybuilders abusing anabolic steroids to increase muscle mass - are at an increased risk of heart dis ease, strokes and liver disease, as well as hair loss, male breast growth, mood swings and even permanent infertility.
Segesterone acetate, also known in its synthetic form by the brand name Nestorone, is a form of the female sex hormone progesterone, which triggers a reaction in a man's brain that makes his testes stop producing sperm.
'In the same way the contraceptive Pill switches off a woman's ovaries, this gel switches off the testes,' Dr Fitzgerald explains.
Along with halting sperm production, the gel also stops the testes from producing natural testosterone, which is vital for healthy bodily function. The added testosterone in the gel replaces the lost testosterone, preventing side effects.
'You don't want a man to be testosterone-depleted,' says Dr Fitzgerald. 'Otherwise you will get side effects such as reduced libido. It is also bad for general health, sense of wellbeing, and the health of muscles and bones.'
The testes may shrink slightly, but not significantly, during use, as sperm production is lower. But no serious adverse effects have been reported to date.
I JUST RUB ON THE GEL BEFORE I GET DRESSED
Dan Glastonbury, 32, from Stretford, Greater Manchester, has been using the gel since May.
He says the only symptom he suffered was a strange, unexpected new allergic reaction to a silver ring gifted to him by his wife of two years, Emily, 29. He now develops an eczema-like rash on his finger if he wears it for too long.
Doctors are not quite sure why and haven't seen this reaction in any other men. Dan considers this just a minor issue, having seen Emily struggle with severe side effects of contraception for years. Emily was on the Pill, and then had a hormone-releasing implant - but they didn't agree with her.
'I had raised anxiety and low moods,' she says. 'I saw an advert for the trial on Facebook and was really intrigued. We don't yet want kids but I really didn't want to be on hormonal contraception any more.'
Over the course of two months, the treatment brought Dan's sperm count down from about 47 million per millilitre to below one million. By the end of August, the couple had begun using the gel as their sole form of contraception.
'To me, a million sounded like a lot, because it only takes one sperm to make someone pregnant,' Dan says. 'But apparently under a million the chances of impregnating someone are very low. So we just trusted in the science.'
Emily adds: 'I have probably felt more confident using this than any other form of contraception we have used because we have the tests and doctors telling us it's working.'
Dan hasn't noticed any changes in his behaviour or sex drive since using the gel, and has found it easy to slot into his morning routine.
'Rubbing on the gel is the last thing I do before I get dressed,' Dan says. 'The best thing is that Emily is so much happier now, not being on anything, which makes me happy - and I'm only slightly inconvenienced to make her life better.'
THE BIG QUESTION IS: CAN MEN BE TRUSTED?
The couples both understand the reservations some may have about entrusting men with the responsibility of contraception.
'I don't think I would have trusted a boy ten years ago to be in charge of fertility,' Emily says. 'At the end of the day, it's my body that would have been affected by pregnancy - both physically and emotionally - not the boy. But this new option will open up a conversation. Women shouldn't constantly be relied on to be in charge of contraception.'
Dan also has some doubts.
'If I had a daughter and she was dating, I would say if a man tells you he's on the gel, do not believe him - use a condom,' he says. 'Men will say a lot of things when they want to have sex.'
John admits to missing a few doses here and there, but dismisses concerns that men are somehow less trust worthy when it comes to contraception.
'We've been together for five years - in the same way I never had any concern or worry about Alex taking the Pill, she doesn't worry about me using the gel,' he says.
The latest trial of NES/T has so far recruited more than 100 couples worldwide - including 52 in Edinburgh and about ten in Manchester - and 420 will be involved overall. It will have to go through further trials in even larger groups of people and secure regulatory approval before it is widely available.
Dr Fitzgerald says: 'A lot of people have asked, "How can you trust a man to use the gel?", but men have trusted women for a long time not to get pregnant. I hope we will get to a point where the decision over who uses the contraceptive is not such a big deal.'