The only birth control options for men are condoms and getting snipped, or more scientifically known as vasectomies, where the vas deferens tubes are closed so as to inhibit sperm from traveling up and out from the testicles. These options take the two extremes and leave a lot of the responsibility for being sexually safe to birth control for women. Other male contraceptives have previously been subject to failure in medical tests because they are either not reversible or do not adequately prevent pregnancy. But some scientists are trying to change that with a male contraceptive called Vasalgel.
Vasalgel is a sticky polymer gel that is injected into the vas deferens to block the sperm from traveling to mix with the semen. Theoretically the gel can be reversed by another injection of plain old baking soda which would dissolve the gel, thus eliminating the physical obstacle blocking the sperm. Scientists have tested the gel on rats and rabbits and rhesus monkeys and it fared particularly well with the monkeys, successfully preventing the 16 males from fathering any offspring for a two year study period, despite their cohabitation and mating with fertile females.
Nevertheless, the gel isn't ready for human use just yet. The study did not include the step of flushing out the gel, so it is not yet proven if reversing the gel's capabilities would be possible. Furthermore, some of the male rhesus monkeys developed a sperm granuloma, i.e. a lump of sperm outside the vas deferens that can be very painful. Not exactly something you want as a side effect from your birth control. Looks like it's back to the drawing board!