The first oral contraceptive pill was available to married women in Britain on the NHS in 1961. From 1967, it was available to all women in the UK and, as the Guardian reports, is now used by 3.5 million British women aged between 16 and 49. Globally, it is taken by around 100 million women.

Researchers have turned their attention to creating a male contraceptive pill, and it seems that is now one step closer to becoming a reality.

Scientists from the University of Washington have revealed that a male contraceptive pill has been found to be effective, safe, and does not harm sex drive.

Sharing their study results at ENDO 2018, the Endocrine Society's 100th annual meeting in Chicago, the research team noted that it appears to be safe when used daily for a month, with hormone responses consistent with effective contraception.

Similar to the pill for women, the experimental once-daily male oral contraceptive, dimethandrolone undecanoate (DMAU), combines activity of an androgen (male hormone) like testosterone, and a progestin.

The study's senior investigator and professor of medicine at the University of Washington, Professor Stephanie Page, commented: "DMAU is a major step forward in the development of a once-daily 'male pill'. Many men say they would prefer a daily pill as a reversible contraceptive pill, rather than long-acting injections or topical gels, which are also in development."

Professor Page believes there has been slow progress in the creation of a male birth control pill as currently available forms of testosterone can cause liver inflammation and clear the body too quickly for once-daily dosing, meaning two doses a day would be required.

DMAU, which is being developed by the National Institutes of Health, Eunice Kennedy Shriver National Institute of Child Health and Human Development, contains undecanoate, a long-chain fatty acid which the researchers believe slows this clearance.

The study at the University of Washington Medical Center and the Harbor-UCLA Medical Center involved 100 health male participants, aged 18 to 50. The trial investigated three different doses of DMAU (100, 200 and 400mg), as well as two different formulations inside the capsules (castor oil and powder).

The dose groups included five subjects randomly receiving an inactive placebo, while another 12 to 15 men received DMAU. Participants took the drug or placebo for 28 days, once daily, with food. The researchers noted that the pill must be taken with food in order to be effective.

In total, 83 men completed the study, giving blood samples on the first and last days of the study for hormone and cholesterol testing.

The results revealed that, at the highest dose of DMAU (400mg), participants showed "marked suppression" of levels of their testosterone and two hormones required for sperm production. These low levels were found to be consistent with effective male contraception observed in longer-term studies.

All dose groups receiving DMAU experienced some weight gain and saw decreases in HDL ("good") cholesterol. However, researchers said these were both mild. All participants passed safety tests, including markers of liver and kidney function.

Professor Page concluded: "These promising results are unprecedented in the development of a prototype male pill. Longer term studies are currently under way to confirm that DMAU taken every day blocks sperm production."