Both men and women are responsible for pregnancy, yet the burden of preventing it often falls on one gender. Women can choose from a variety of options to control fertility while for generations, men have been limited to withdrawal, condoms and sterilization. But someday soon, a new method may allow men to shoulder a greater share of responsibility, CNN reports.

A new hormonal birth control shot for men effectively prevented pregnancy in female partners, a new study found.

The study, co-sponsored by the United Nations and published Thursday in the Journal of Clinical Endocrinology and Metabolism, tested the safety and effectiveness of a contraceptive shot in 320 healthy men in monogamous relationships with female partners. Conducted at health centers around the world, enrollment began on a rolling basis in September 2008. The men, who ranged in age from 18 to 45, underwent testing to ensure that they had a normal sperm count at the start.

The injection, given every eight weeks, consisted of 1,000 milligrams of a synthetic form of testosterone and 200 milligrams of norethisterone enanthate, essentially a derivative of the female hormones progesterone and estrogen referred to as "progestin" in the synthetic form.