A new form of male birth control has been deemed safe by researchers testing the new drug on a group of men.

The pill is the second promising oral contraceptive in the works for men, and both are following in the steps of a birth control gel that is currently in clinical trials.

It's a major milestone, but it hardly means doctors will be writing prescriptions tomorrow. In fact, it will likely be 10 years before male contraception is available.

But this far into the developmental and approval process, researchers at Los Angeles Biomed Research Institute and the University of Washington are pleased to report the drug safely reduces hormones required for sperm production without killing men's sex drives.

A daily birth control pill for men has proven safe in early-stage clinical trials, a new study reveals - but it could be a decade before men are the ones on the pill, scientists say

The entirety of human ingenuity has only produced three options for men to participate in pregnancy prevention.

And they exist at two extremes: a vasectomy - a surgical procedure to block sperm from making its way into semen - is a very long-term solution, while condoms and the 'pull out method' are only effective as often as you use them.

There are lots of options for women, on the other hand, but none is without its side effects, and almost all forms disrupt women's hormones in order to prevent pregnancy.

Long-acting methods like have to be inserted, a process that is very painful for some women, and 'painless' pills can cause weigh gain and nausea.

So male birth control is a long-awaited innovation, anticipated and hoped for by both men who want contraception to be in their control and women who don't want to bear the burden of birth control.

Its development has finally gained some momentum in recent years, with a gel rubbed on the back and shoulders leading the pack (drawing both excitement and ire from women whose contraceptives are often more invasive).

The gel is currently in clinical trials, which are set to conclude around 2022.

Now, the oral male contraception has passed muster in its first major test for safety, the researchers report.

The new drug, 11-beta-MNTDC, is a modified synthetic form of testosterone.

It acts both on male hormones, called androgens, and on progesterone, a hormone produced in women's ovaries to facilitate pregnancy and by the male endocrine system to produce testosterone.

The idea is that 11-beta-MTDC should diminish sperm production in the testes while maintaining normal testosterone levels throughout the rest of the body.

In their tests on 40 adult men - 10 of whom got placebos - the drug appeared capable of reducing hormone production down to levels of someone who is androgen deficient.

The men took a daily dose of either 200 or 400 mg with food for 28 days.

At the end of the study period, no one had quit the drug, although some experienced mild side effects such as fatigue, headaches or acne.

Five men said their libidos were a bit lower, but they all maintained their sex lives as usual.

Although the levels of their hormones fell significantly, the researchers say that it would take between 60 and 90 days for sperm count itself to decrease, the drug effectively hampered production of the two hormones involved in making sperm.

Men's testes make 1,500 sperm a second, which is both a reason that it takes so long for the new contraception to take effect and part of the explanation for why male birth control hasn't been developed sooner.

That certainly isn't the only reason though, as some attempted drugs caused liver damage and pharmaceutical companies have generally been unmotivated to make male birth control.

The Los Angeles Biomed and University of Washington scientists can't yet say for sure that the drug works, but they know it is safe, and its effects thus far are promising.

Its development follows the same company's safety testing of another pill for men.

'The goal is to find the compound that has the fewest side effects and is the most effective,' said Dr Stephanie Page, a professor of medicine at the University of Washington School of Medicine.

Whichever pill proves itself, it will be some time before either is publicly available. The next stages of the drug approval process take two and three years, respectively, and the FDA's own assessment can take about two years.

But, better late than never.

'Safe, reversible hormonal male contraception should be available in about 10 years,' said co-investigator Christina Wang, an associate directer at Los Angeles Biomed Research Institute.