What Is It?

The birth control patch is a thin, beige, 1¾-inch (4½-centimeter) square patch that sticks to the skin. It releases hormones through the skin into the bloodstream to prevent pregnancy. Hormones are chemical substances that control the functioning of the body’s organs.

How Does It Work?

The combination of the hormones progesterone and estrogen in the patch prevents ovulation (the release of an egg from the ovaries during a girl’s monthly cycle). If an egg isn’t released, a girl can’t get pregnant because there’s nothing for a guy’s sperm to fertilize.

The hormones in the patch also thicken the mucus produced in the cervix, making it difficult for sperm to enter and reach any eggs that may have been released. The hormones can also sometimes affect the lining of the uterus so that if the egg is fertilized it will have a hard time attaching to the wall of the uterus.

Like other birth control methods that use hormones, such as thebirth control pill or ring, a girl uses the birth control patch based on her monthly menstrual cycle. She puts on the patch on the first day of her menstrual cycle or the first Sunday after her menstrual cycle begins. She will change the patch on her skin once a week for 3 weeks in a row. (The patch should be applied to one of four areas: the abdomen, buttocks, upper arm, or upper torso — except for the breasts.) On the fourth week, no patch is worn, and a girl’s period should start during this time.

How Well Does It Work?

Ongoing studies suggest the birth control patch is as effective as the birth control pill. That means that about 8 out of 100 couples will have an unintended pregnancy during the first year of use. Of course, the chance of getting pregnant depends on whether you use the patch correctly. Delaying or missing a weekly application or removing a patch too early reduces its effectiveness and increases the chance a girl will become pregnant.

For girls who weigh more than 198 pounds (90 kilograms), the contraceptive patch may be less effective in preventing pregnancy.

In general, how well each type of birth control method works depends on a lot of things. These include whether a person has any health conditions or is taking any medications that might interfere with the patch. How effective the patch is at preventing pregnancy also depends on whether the method chosen is convenient — and whether the person remembers to use it correctly all the time.