The potential routes of contraceptive control over male fertility are as varied as those for females. The male contraceptives on the market today – condoms and vasectomies – are respectively a physical barrier to semen and a surgical barrier to sperm. Some emerging methods of male contraception improve upon the barrier concept; some block the production of sperm altogether; some alter the sperm so that they are not functional.

	Endocrine approach	Disrupting the manufacturing of the hormones in the pituitary gland and the testes – these hormones are required for the triggering and regulation of sperm production	Hormonal male contraceptives
	Immunological approach	Using the body's own immune response to disrupt some aspect of the reproductive system	Eppin
	Testicular targets	Disruption of germ cell differentiation, disruption of spermatid adhesion to Sertoli cells	Indazoles, Indenopyridines, Adjudin
	Epididymal targets	Sperm maturation and glycoprocessing (adding membrane-bound molecules along the sperm's surface)	Drugs disrupting HE6 or glycosphingolipid metabolism
	Chemical disruption of ejaculation	Stopping the smooth muscle contractions which move sperm along the vas deferens	“Dry orgasm” pill
	Disruption of sperm motility (movement)	Preventing ejaculated sperm from using their cellular energy resources efficiently, making them partially or fully immobile	Drugs which block sperm membrane calcium ion channels, drugs blocking SFEC1
	Disruption of sperm-egg fusion	Preventing ejaculated sperm from recognizing or binding to an egg in the female reproductive tract	HEX-B enzyme inhibitor
	Physical barriers to sperm	Partially or fully blocking the vas deferens (the tube though which mature sperm move from the epididymis to the urethra) with implanted or injected materials	American & Chinese designs of the Intra Vas Device (IVD), RISUG
	Local application of heat	Prevents the production of mature sperm using the body’s own quality control mechanism – successful spermatogenesis requires a temperature several degrees below body temperature	External heat, suspensory underwear

Some targets in the male reproductive system are more challenging to reach than others thanks to a cellular boundary known as the blood-testis-barrier (BTB). Similar in function to the blood-brain-barrier, the BTB prevents the passage of toxins from the bloodstream into the genetically sensitive tissues of the testes. The BTB protects the seminiferous tubules where spermatogenesis takes place. For this reason, drug targets within the testes can be difficult to reach. A group of researchers at the Population Council in New York devised a clever way around the BTB. They created a slightly modified hormone (follicle stimulating hormone or FSH) which could pass the BTB but did not have any of the hormonal functions of FSH. Generally speaking, drugs targeting cells outside the BTB, such as epididymal cells, will be easier and cheaper to formulate.

Barrier methods of male contraception face a special reversal challenge. Most of these methods aim to have a reversal procedure less complicated and less expensive than vasovasostomy (microsurgical vasectomy reversal). Some designs – such as the Chinese Intra Vas Device and RISUG – allow vasal fluid to pass through the vas deferens. The designers hope this will prevent the build-up of pressure in the epididymis and avoid an induced immune response to sperm cells. The reversibility of these barrier methods has been proven in primate models, but not yet in men.

One oft mentioned challenge is, in fact, not a challenge at all. The suggestion that male fertility is fundamentally more difficult to control than that of females is misinformed. The male and female reproductive systems are functionally analogous, and equally receptive to birth control. Furthermore, complete suppression of spermatogenesis (azoospermia) is not required for highly effective male contraception. A typical man has between 20 and 60 million sperm per milliliter of semen. The Male Hormonal Contraception Summit members have issued a consensus statement that a high level of contraceptive effectiveness can be achieved with as many as 1 million sperm per milliliter remaining.