US scientists are developing a male birth-control gel that rubs into the shoulders.
The hormonal contraceptive is made up of the drug Nestorone. This contains a form of progesterone that blocks the male hormones required to make sperm.
It also has testosterone to replace that blocked by Nestorone.
A man’s swimmers reportedly return back to normal once he stops using the gel.
A trial is being carried out at the University of Kansas, with researchers claiming no participating couple has become pregnant since it started in October 2018.
They are urging others to sign up, but warn couples must be “willing to accept a low but unknown risk of pregnancy” while they ascertain the gel’s effectiveness.
The study, which is being carried out in the UK and US, hopes to recruit 420 men and women, according to ClinicalTrials.gov.
It is unclear how many have signed up so far or when the gel may be available to the public.
The male participants must apply the transparent gel to their arms and shoulders every day for a year.
“Contraceptive efficacy” will be monitored over the 12 months to estimate “pregnancy population in the typical use population”.
The men will then be followed for a further year to determine if their sperm count returns to normal.
Side effects are not thought to be a concern after “Nestorone has been tested and shown to be safe”, according to StudyPages.
Couples may receive up to $4,125 (£3,148) for taking part.
Visit the StudyPages website to find out if you are eligible.
The controversy of male birth control
Women often shoulder the burden of contraception, with two-thirds of those aged 20-to-24 in the UK taking the pill, according to the sexual-health charity FPA.
Sterilisation is more common in men, however, with 28,000 vasectomies being carried out in NHS hospitals in 2005.
This is compared to 18,000 female sterilisations.
In the US, 15.9% of women aged 15-to-44 use the pill, while 8% rely on the “coil” or implant, and 14.3% are sterilised, according to the Centers for Disease Control and Prevention.
Talk of a “male pill” has been circulating for some time, with several drugs in development.
Yet with men not having to contend with pregnancy, many women worry how strict their other half will be at taking the contraception as prescribed.
Taking control out of a woman’s hands may also leave her at risk if she engages in casual “one night stands”.
Yet it seems many women support male birth control.
In response to the contraceptive gel, one woman said: “I think it’s great. Men should be just as responsible as ladies.”
Another added she would “absolutely” trust men to apply the gel as required, CBS Detroit reported.