A male contraceptive pill has been developed which is effective, safe and does not harm sex drive, scientists have announced.
In what has been described as a "major step forward", the drug was successfully tested on 83 men for a month for the first time, the Daily Telegraph reports.
So far efforts to create a once-daily pill to mimic the mainstream female contraceptive have stalled because men metabolise and clear out the hormones it delivers too quickly.
It means temporary male contraception has relied on condoms alone, with the the main hopes for future contraceptive developments resting on a long-acting injection or topical gel, both of which are also underdevelopment.
However, the new drug, called dimethandrolone undecanoate, or DMAU, includes a long-chain fatty acid which slows down the clearance, allowing just one dose to be taken each day.
Like the pill for women, the experimental pill combines activity of an androgen - a male hormone such as testosterone - and a progestin.
Investigators at the University of Washington Medical Centre tested three doses of DMAU - 100, 200 and 400mg - on 100 healthy men between 18 to 50 years old, 83 of whom completed the study.
They were subject to blood sampling for hormone and cholesterol testing on the first and last days of the study.
At the highest dose of DMAU tested, 400 mg, subjects showed "marked suppression" of levels of their testosterone and two hormones required for sperm production.
The results showed that the pill worked only if taken with food. "Despite having low levels of circulating testosterone, very few subjects reported symptoms consistent with testosterone deficiency or excess," said Professor Stephanie Page, senior investigator on the study.
"These promising results are unprecedented in the development of a prototype male pill," All groups taking DMAU experienced some weight gain, as well decreases in HDL ("good") cholesterol.
However, all subjects passed their safety tests, including markers of liver and kidney function. "DMAU is a major step forward in the development of a once-daily 'male pill'," said Page.
"Many men say they would prefer a daily pill as a reversible contraceptive, rather than long-acting injections or topical gels, which are also in development."
Contraceptive pills for females have been available for almost 70 years, although the only achieved widespread use in Britain, including availability on the NHS, in 1961.
However, other than the condom, which were first invented in 1855, there have never been a temporary male contraceptive.
Male hormone injections
Progestogen jabs to cut off sperm production were found to be 96 per cent effective in clinical trials at University of Edinburgh last year. Research stalled due to side effects, including depression, mood disorders, libido changes and acne (which may sound familiar to women who've used the contraceptive pill)
Male contraceptive gel
A non-hormonal and non-surgical 'reversible' vasectomy, Vasalgel would be injected into the vas deferens, the small duct between the testicles and the urethra, to block sperm from being released. After successful tests on animals, the first clinical trials are expected to be finished in 2020.
A computer-activated version of the levonorgestrel implant, this device being developed at MIT could last 16 years and let women turn off the hormone release using a wireless remote control.
Researchers at the University of California, Berkeley are testing a Catsper blocker, to stop sperm from entering and fertilising an egg. In women, it would be effective within a short window after sex. In men, it could work like the daily contraceptive pill, but it is unlikely to be on shelves for at least a decade.