It causes changes in the uterus and fallopian tubes that kill sperm.

It makes the uterus and fallopian tubes produce fluid that kills sperm.

So far they've managed to isolate an ingredient which kills human sperm extremely quickly and efficiently.

To be effective they need to be used with spermicide - a special cream or pessary that kills sperm.

A spermicide is a substance that kills sperm.

American researchers report that ultrasound waves can be used effectively to kill sperm, potentially offering a new male contraceptive method.

There is evidence that it kills sperm.