A second viable option for male hormonal birth control has passed the rigorous human safety tests and and shown promising results, U.S. researchers say.

The drug is a “modified testosterone” that combines the actions of a male hormone called androgen and a progesterone that work together as a contraceptive.

"Our results suggest that this pill, which combines two hormonal activities in one, will decrease sperm production while preserving libido," Dr. Christina Wang, of the Los Angeles Biomed Research Institute (LA BioMed) at Harbor-UCLA Medical Centre, said in the report.

Wang is the co-senior investigator in the research, along with Dr. Stephanie Page of the University of Washington School of Medicine.

They’re testing the drug 11-beta-methyl-19-nortestosteronedodecylcarbonate, known as 11-beta-MNTDC, at their respective facilities.

The phase 1 study results were presented on Sunday at ENDO 2019, the Endocrine Society’s annual meeting held in New Orleans, La. -- the same conference where Page and Wang presented their findings on another male birth control pill, drugdimenthandrolone undecanoate, or DMAU, the previous year.

"The goal is to find the compound that has the fewest side-effects and is the most effective," Page said.

Page said in an email to CTV News that 11-beta-MNTDC is “related but distinct” from its “sister compound” DMAU.

Page told ENDO 2019 attendees plan to use the two oral drugs “in parallel in an attempt to move the [contraceptive medicine] field forward.”

The study had 30 healthy men at LABioMed and the University of Washington in Seattle take one of two doses, (14 men took 200 milligrams, 16 men received 400 mg) of 11-beta-MTNDC, while 10 study participants took a placebo, for 28 days.

The results were promising -- hormone responses from test subjects were consistent with effective contraception.

The men who received 11-beta-MNTDC had their average circulating testosterone level drop, but did not have any serious side-effects. The side-effects reported ranged from fatigue, acne or headache in four to six men each according to Wang. Five men reported a decreased sex drive, while two described mild erectile dysfunction, but Wang said sexual activity was not decreased.

Page said that effects due to low testosterone were minimal as “11-beta-MNTDC mimics testosterone through the rest of the body but is not concentrated enough… to support sperm production.”

Wang predicts, "safe, reversible hormonal male contraception should be available in about 10 years."