Why is it so difficult to create a male contraceptive pill?
Men produce millions of sperm during the course of one day, all of which have to be stopped to achieve effective contraception. This makes contraception in men
more difficult than in women, who only produce one fertile egg at a time. Another difficulty with the pill for men lies in the delicate balance between stopping sperm while keeping sexual function and libido intact.
In principle, this could be achieved by blocking the action of the hormone testosterone so that the testicles no longer produce any sperm. Studies on the active ingredient progesterone (which is used in many contraceptive pills for women) found that a progestogen pill for men could indeed work but different men react differently to the pill. During trials, researchers observed that some men still produced a reduced number of sperm, which means that they could still make a women pregnant.