Plan B is a contraceptive that can be used after a woman has had unprotected sex and wishes to prevent a pregnancy. While it is a safe and effective way to prevent a pregnancy, the manufacturer's directions must be followed in order to ensure maximum effectiveness.

What Is Plan B?

Plan B is the brand name of emergency contraceptive pills manufactured by DuraMed Pharmaceuticals. Emergency contraception pills combine synthetic hormones into one large dose and can prevent unintended pregnancy when taken within a limited number of hours after unprotected sex.

How Does Plan B Work?

The mechanism by which Plan B operates involves the delaying or prevention of ovulation, which means the ovary will not produce an egg for sperm to fertilize. Without a viable egg, the sperm have nowhere to go and will eventually die off.

If a woman takes Plan B after she already has ovulated for the month, the hormones in the emergency contraception pills will make a fertilized egg unable to attach to the wall of her uterus. Without this action, the resulting embryo, if it exists, will be expelled during menstruation without the woman ever knowing.

When to Take Plan B

A woman who has had unprotected sex and doesn't want to risk pregnancy must take Plan B within 72 hours of intercourse. Because conception typically occurs within three to five days of intercourse, Plan B must be taken within the lower threshold of that time frame. Plan B is not effective in terminating an existing pregnancy, so once the embryo has attached itself to the uterine wall, emergency contraception is ineffective.

How Effective Is Plan B?

While the effectiveness of Plan B emergency contraception is generally reliable when taken within 72 hours of intercourse, it is most effective when taken as soon as possible. When taken within three days after sex, Plan B's success rate is 87 percent.

Where to Buy Plan B

Plan B is available at pharmacies and family planning clinics nationwide. While it was once a prescription-only medication, it is now available over-the-counter. To purchase it, be prepared to show your state-issued ID, as you must be 18 or older. The cost ranges from $25 to $60, depending on location.

Considerations for Taking Plan B

It is important not to rely on Plan B as your sole source of birth control. Taking birth control pills or utilizing other methods of contraception boost the odds of preventing a pregnancy. Because Plan B does not protect against sexually transmitted diseases such as HIV, it is important to use condoms unless you and your partner have both been tested for STDs and are monogamous.