At the website HowStuffWorks there's an interesting piece on the next generation of male contraceptives, which might be a little discomforting if you're a guy. From the piece:
Men, on the other hand, present a greater challenge. Driven by eons of evolution involving complex processes of the endocrine and reproductive systems, men produce tens of millions of sperm per day. To prevent pregnancy, every one of those specialized cells -- think of them as DNA-packed Olympic swimmers -- must be blocked, hamstrung or killed. It's a daunting task, especially when you consider the timelines involved. It takes 75 days for sperm fashioned in the testes to mature in a tightly coiled companion structure known as theepididymis. That means an intervention that blocks sperm production won't become fully protective for two and a half months. And men who go off such an intervention would have to wait the same length of time before their fertility returns.
Because of these challenges, the search for the perfect male contraceptive -- one that's 100 percent effective, easy to use, reversible and free of side effects -- has been elusive.
Read the whole article at HowStuffWorks.