Like other methods of birth control, the birth control patch releases hormones. Hormones are chemicals made in our bodies. They control how different parts of our bodies work.

The hormones in the patch are the same hormones as in the birth control pill — estrogen and progestin.

The hormones in the birth control patch work by

Keeping eggs from leaving the ovaries. Pregnancy cannot happen if there is no egg to join with the sperm.

Making cervical mucus thicker. This keeps sperm from getting to the eggs.

Effectiveness is an important and common concern when choosing a birth control method. The birth control patch is very effective. It works best when it is always placed on the skin on time. That keeps the correct level of hormone in a woman’s body.

Less than 1 out of 100 women will get pregnant each year if they always use the patch as directed.

About 9 out of 100 women will get pregnant each year if they don’t always use the patch as directed.

The patch may be less effective for women who are overweight. Talk with your health care provider if you are concerned about how well the patch may work for you.

Most women can use the patch safely. But all medications have some risks, so safety is a concern when choosing a birth control method. Serious side effects of the birth control patch, though rare, may be more likely if you have certain conditions. Some of these conditions may even rule out using the patch. Talk with your health care provider to find out if the patch is likely to be safe for you.

• are pregnant

• get migraine headaches with aura

• have certain inherited blood-clotting disorders

• have had blood clots or vein inflammation

• have had breast or liver cancer

• have had a heart attack, stroke, or angina

• have had serious heart valve problems

• have lupus with certain conditions

• have serious liver disease

• have uncontrolled high blood pressure

• have very bad diabetes

• smoke and are 35 or older

• smoke and have high blood pressure

If you have a condition that makes it unsafe to use the patch, don’t worry. There are many other methods of birth control that may be safe for you if you cannot use it. Read about other methods to find one that is right for you.

To find out what day is best for you to start using the patch, talk with your health care provider. Most often, women start using the patch within the first five days after the start of their periods. That way, they are protected against pregnancy right away. That means that if your period starts on a Wednesday morning, you can apply the patch as late as the following Monday morning to be protected right away.

If you start the patch later than five days after the start of your period, protection will begin after seven days. Use another method of birth control — like a condom, female condom, diaphragm, or sponge — if you have vaginal intercourse during the first week of use.