The new pill is known by the chemical name dimethandrolone undecanoate, or DMAU.
One of those was the tendency of available forms of testosterone to cause liver inflammation.
DMAU, which is in part funded by the National Institutes of Health, was evaluated on 100 healthy men, ages 18- to 50-years-old over the course of one month. "A long fatty acid chain has been added to another portion of the molecule to increase its absorption in the blood stream, so we can get around the twice-a-day dosing".
The once-daily prototype pill suppressed certain hormones to the low levels you'd expect to see with effective longer-term contraceptives, results from an ENDO 2018, the Endocrine Society's annual meeting in Chicago, abstract show.
The journey of creating such a pill has not been free of challenges that puzzled the scientists but they have managed to pass over them and to reach the point at which they were able to produce 100% working and safe contraceptive pills for men.
At the highest dose of DMAU tested (400 mg), the men showed "marked suppression" of levels of their testosterone and the two hormones.
Low testosterone levels can lead to loss of sex drive and fatigue, but most of those on the trial did not appear to suffer.
Researchers who conducted a month-long trial involving 83 men said the once-daily pill lowered hormone levels similarly to other forms of longer-term contraceptives-without signs of testosterone deficiency or excess. DMAU must be taken with food to be effective, said Page.
Dr Page said longer term studies are now underway to confirm that when taken every day, DMAU blocks sperm production.
A daily pill for males has always been elusive to pharmaceutical developers, as oral testosterone in previous forms may damage the liver or clear the body too quickly to work in just one pill per day.