The contraception injection was a form of birth control used in the Federation. The medicine had to be administered regularly, otherwise intercourse could lead to fertilization and pregnancy.
In 2375, Benjamin Sisko, preoccupied by the latter stages of the Dominion War, forgot to renew his injection, despite repeated reminders from his CMO, Julian Bashir. As a result, his wife, Kasidy Yates, became pregnant with their child, the couple's first. (DS9: "The Dogs of War")
- This is the only ever reference to birth control in the history of Star Trek.