ananyo writes "Developing oral contraceptives for men has not gone as swiftly as researchers imagined in the early 1970s; they suggested at the time that a 'male pill' was not far off. But researchers now report a new way to make male mice temporarily infertile. Although the treatment is not ready for human use, the method avoids some of the pitfalls of earlier attempts. The technique appears to have a much more specific action than previous methods: it impairs sperm production by blocking a protein called BRDT. This protein was singled out as a potential therapeutic target five years ago because it only occurs in the testes, where it is required for the division of sperm cells. If the approach proves safe in humans, it would be an improvement over hormone-based methods of male contraception, which are not completely effective and cause side effects such as mood swings, acne and a loss of libido (abstract). On the downside, however, the compound 'shrank the mice's testes.'"