How does Plan B stop someone from getting pregnant when the sex is already done? What will it do to someone's body after they take it? I can't tell you how many times I've heard stories about my friends rushing to CVS the morning after sex to buy one of these little pills to help prevent pregnancy. And I've always wondered how they work. Before you run to the local pharmacy after a night that has an unforeseen circumstance, make sure that you know what you're actually doing to your body. 

How It Prevents Pregnancy

Plan B is not 100% effective. No form of birth control is 100% effective. You can take Plan B anywhere within 72 hours after sex. It's most effective in the most recent hours, but as the 72-hour mark hits, it's still about 90% effective. So it won't guarantee a prevented pregnancy, although it's pretty close.

According to Plan B's website, it essentially interferes with your cycle depending on where you are. So it will either delay ovulation, prevent fertilization, or not allow an egg to attach to the uterus. It pretty much does whatever it needs to do to ensure that you don't get pregnant. 

Side Effects

Like any other medicine, Plan B has immediate side effects. Its most common side effect is nausea. While being nauseous for a day or so is a lot better than the alternative of having morning sickness for a couple of months, if you throw up the pill it may lose its effectiveness. It can also affect your cycle and you may have some spotting, so just be wary of that. 

In the Long Run

Here's where the rumor mill had me wanting to do some research: I heard that you can only take a morning after pill a certain number of times before it affects your fertility. And I totally bought into it. I mean realistically something that just halts your natural body processes so that you don't get pregnant can't be good in the long run, right?

This is probably the only time I'll ever admit it, but I was wrong. Currently, there is no evidence that taking an emergency contraceptive will affect your fertility in the long run. However, these pills are called Plan B for a reason. They're designed to be used once—when a condom breaks, when you forget to take your birth control, or when your partner didn't pull out in time. Plan B pills should not be used as a primary method of birth control. 

If you're taking Plan B often, you should reconsider your primary methods of birth control. First of all, Plan B isn't cheap. If you're fairly sexually active and taking it often it can really break the bank. Second of all, it doesn't protect against STDs. So while you may not be pregnant and your fertility may not be affected, you may find yourself with a disease that can hurt you in the long run.

Moral of the story: it's okay to take Plan B. Everybody makes mistakes and the morning after pill is an effective way to save your ass when those mistakes could be life-changing. But if you find yourself relying on it, it might be time to make some changes.