If you always forgot to take your daily birth control pill, the longer-term pregnancy-prevention method known as the IUD may have been your saving grace. But the non-hormonal copper IUD has another unexpected superpower: It’s 99.9 percent effective at preventing pregnancy if inserted within five days of unprotected sex.

The IUD, which stands for intrauterine device, is a tiny, T-shaped device that sits in the uterus to prevent pregnancy, according to Kecia Gaither, MD, director of perinatal services at Lincoln Medical and Mental Health Center. Learn more about IUDs for birth control.

There are two types of IUDs: hormonal and non-hormonal IUD. The hormonal IUD uses progestin to prevent pregnancy. A non-hormonal IUD, which includes the copper IUD, adds no estrogen or progestin to the body, which appeals to many women.

So, How Does the Copper IUD Prevent Pregnancy?

The small amount of copper in this IUD creates a toxic environment for sperm so they can’t swim to an egg (but it’s totally safe for you and your uterus). And you can leave it in for up to 12 years.

Even though the copper IUD can prevent pregnancy if inserted within five days of unprotected sex, Dr. Gaither doesn’t recommend using it for the short term. (Learn more about the process of getting an IUD inserted.) “If you’re going to go through the effort of getting the IUD inserted, I wouldn’t use it only for emergency birth control—you’d want to keep using it long term,” says Dr. Gaither.


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