Indian scientists have developed a reversible and injectable method of birth control for men that’s been 100% effective in trials

RISUG is an injectable compound that blocks the passage of sperm for up to a decade. It begins working instantly, is easily reversible, and has few side effects. Right now, RISUG looks like the most promising of potential reversible male contraceptives. The name is an acronym for Reversible Inhibition of Sperm Under Guidance. 

It effectively defertilizes sperm, preventing pregnancy. It has already been tested on men, and none of them have had any complications. So far, it has had a 100% success rate in preventing pregnancy. RISUG has been such a rapid scientific success that it is moving forward in both the US and India. 

(Source)