It's a very frustrating fact of life: sometimes, no matter how careful you are, birth control just fails. Maybe the condom broke or slipped off, maybe you had a hectic day at work and forgot to take your pill. Whatever the cause, when your birth control isn't used appropriately, you gotta act fast.
There to save the day is Emergency Contraception (EC), casually known as "The Morning-After Pill". EC can be taken to prevent pregnancy up to 120 hours (five days) after unprotected vaginal intercourse. It does this by preventing ovulation: if your ovaries haven't released an egg, there's nothing for the sperm to fertilize, and viola -- no fetus! The sooner you take EC, the more effective it is, so don't stall!
The brand names of EC are Plan B One-Step, ella, and Next Choice. The cost can usually range anywhere from $10-70 and can be picked up from nearly any pharmacy. Here is a coupon for $10 off of Plan B One-Step.
If you have an unlucky night and end up needing some form of emergency contraception, you can usually expect a few icky side effects. Most people end up having a bit of nausea and vomiting. When I had the displeasure of partaking in EC (I got Next Choice, I believe) my largest complaint was the dizziness. Spotting is also common. Luckily, side-effects usually clear up within a day or less.
Here's a fun, little-known fact: the Paragard IUD insertion can actually be used as a form of emergency contraception as well! Same rules as the morning-after pill: have it inserted within 120 hours, and it can be effective in preventing pregnancy. This can be quite a bit more expensive, though. It also requires a gynocologist visit, which must be scheduled, and that's a bit tricky when things are time-sensitive. But it is an option!
All in all, the morning-after pill is a safe, effective way to prevent pregnancy if your preferred form of birth control fails. It causes no harm to the body, other than perhaps a day of feeling queasy. It's not something that I would recommend as your everyday form of birth control, but as a back-up when you need it, emergency contraception can work wonders.