What are the hormones in hormonal birth control?

Hormonal birth control works by releasing hormones into the body to help prevent pregnancy. The hormones may be delivered with pills, patches, shots, intrauterine devices (IUDs), implants, or a ring that is placed in the vagina.

The best-known example of a hormonal contraceptive is the birth control pill. The first birth control pill became available in 1960. Today, birth control pills are the most widely prescribed hormonal contraceptive in the United States.

Below, you'll find answers to frequently asked questions about hormonal contraceptives, such as: What hormones do hormonal contraceptives contain? How do hormones help prevent pregnancy? And how do you decide whether to use a hormonal or non-hormonal method (or both)?

The hormones in hormonal contraceptives

Hormonal contraceptives contain lab-made versions of the hormone progesterone, called progestin. Some hormonal contraceptives contain a combination of progestin and a lab-made version of the hormone estrogen. These hormones prevent pregnancy in three different ways:

• They stop the ovary from releasing an egg, which means there is no egg in the womb for sperm to fertilize.
• They thicken cervical mucus, which creates a sticky barrier that makes it difficult for sperm to reach an egg.
• They prevent the lining of the uterus from thickening. This makes it difficult for a fertilized egg to implant in the uterus. This is also the reason why people taking continuous hormonal birth control do not have menstrual periods but may experience withdrawal bleeding.

It's important to remember that this is a simple explanation of how hormonal contraceptives work. There are important differences between different types of hormonal contraceptives, including how quickly they begin to work to prevent pregnancy and their overall effectiveness. Occasionally, backup contraception may be necessary. A healthcare professional will be your best source of information.

It's also important to remember that hormonal contraceptives do not protect against sexually transmitted infections (STIs).

Hormonal contraceptives and side effects

Hormonal contraceptives are generally safe for most people and, when used correctly, are very effective in preventing unplanned pregnancies.

Hormonal contraceptives may also be prescribed for reasons unrelated to contraception. They may be used to help regulate an irregular menstrual cycle or to treat conditions such as heavy and painful periods, menstrual migraines, and endometriosis (a condition in which tissue similar to the lining of the uterus grows outside the uterus).

As with any medication, there is a risk of side effects. These vary depending on the contraceptive used and the hormones it contains. Progestin-only contraceptives and progestin-estrogen contraceptives have different side effects. Some common examples of side effects include irregular menstrual bleeding, nausea, weight gain, acne, and headache. (This is not a complete list of side effects; you should consult the contraceptive's prescribing information for a complete list.)

Smokers over the age of 35, people with certain medical conditions and those taking certain medications should not use hormonal contraceptives. Before starting any treatment, your healthcare provider will need detailed information about your medical history and a list of all the medications you take (including over-the-counter medications and supplements).

Again, your healthcare provider will be your best source of information about contraceptives and decisions about your health.