They can’t stop until people aren’t fertile. From the NYT, the chase for testicular toxins:
The most studied approach in the United States uses testosterone and progestin hormones, which send the body signals to stop producing sperm. While effective and safe for most men, they have not worked for everyone, and questions about side effects remain.
So scientists are also testing other ways of interrupting sperm production, maturation or mobility.
One potential male birth control pill, gamendazole, derived from an anticancer drug, interrupts sperm maturation so “you’re making nonfunctional sperm,” said Gregory S. Kopf, associate vice chancellor for research administration at the University of Kansas Medical Center. The center has begun discussions with the Food and Drug Administration about the drug, already tested in rats and monkeys.
Dr. John K. Amory, a reproductive scientist at the University of Washington, is studying a drug that was developed for worm infections and was later tried on men because it caused infertility. Using rabbits, Dr. Amory said, he discovered the drug blocks production of retinoic acid, important for sperm production.
Anticancer drugs, worm infections. What happens if a “nonfuntional sperm” cracks into an egg? Is it non-motile or non-genetic-code-bearing? Hell, not that it matters anyway. Maybe these Ph.D folks in hot pursuit of science can partner up with these smarter-than-everyone-else-but-devoid-of-any-trace-of-ethics-geneticists. Then again, maybe not. You never know: after feminizing fish for generations on synthetic estrogen, maybe the male pill will balance the equation somehow, creating a new generation of completely asexual fish incapable of reproduction. I’m sure an environmentalist somewhere will tell us that the planet would benefit somehow with fewer fish in the sea, anyway, right?