Birth control pills don’t actually contain progesterone — they contain a synthetic version of it called progestin.

Progesterone is a naturally occurring hormone in the body. The adrenal cortex, ovaries, and testes produce it.

As its name implies, the hormone is pro-gestational, which means its primary role is to promote pregnancy, says Maria Sophocles, MD, OB-GYN, medical director of Women’s Healthcare in Princeton, New Jersey.

More specifically, the body produces more progesterone after ovulation — the time of the month when the ovaries release an egg down to the fallopian tubes — which causes the uterine lining to thicken.

The thicker uterine lining gives an egg fertilized by a sperm (blastocyst) something to stick to, triggering the placenta to form.

Meanwhile, if a sperm doesn’t fertilize the egg, progesterone levels drop, causing the menstrual cycle to commence.

Altering your progesterone level with hormonal birth control can affect your ability to become pregnant.

While no hormonal contraception contains progesterone, many contain a synthetic version of it called progestin, says Sophocles.

“Progesterone and progestin have similar actions but are chemically different,” says Carolyn Ross, MD, OB-GYN, medical advisor at Stix. “So, while they have similar effects, progesterone and progestin are not identical.”

Progestin effectively prevents pregnancy by essentially tricking the body into thinking it’s pregnant.

The body registers the progestin as progesterone, so the higher “progesterone” levels cause the body to enact several processes that it would if you were pregnant.

This includes halting ovulation, thickening cervical mucus so that sperm are unlikely to reach the egg, and thinning the lining of the uterus so that the blastocyst can’t attach to it.

There are a few types of progestin used in birth control, says Sophocles.

“All types of progestin work by inhibiting ovulation and by causing mucus in the cervix to thicken, thereby limiting the ability of sperm to get through the cervix into the uterus,” she explains.

Currently, there are four kinds of hormonal birth control that control progestin, says Sophocles.

Known colloquially as the “minipill,” progestin-only birth control pills are typically 93% effective at preventing pregnancy. When taken daily at the same time, these pills are at least 99% effective.

Hormonal IUDs are long lasting forms of birth control that use a progestin called levonorgestrel. The hormonal IUD is more than 99% effective and usually poses no risk of user error.

The birth control shot (Depo-Provera) involves injecting progestin to prevent pregnancy. Each shot effectively prevents pregnancy for up to 3 months. With continued use — marked by getting the shot once every 11–13 weeks — the method is more than 99% effective.

Known as a birth control implant or birth control rod, Nexplanon contains a form of progestin called progestin etonogestrel. It’s placed inside the arm and can prevent pregnancy for up to 4 years. It’s more than 99% effective.

There’s no such thing as an estrogen-only contraceptive. That’s because estrogen, on its own, can’t effectively prevent pregnancy, says Sophocles. “It’s progestin that prevents the pregnancy,” she says.

However, sometimes, birth controls contain estrogen and progestin because this helps regulate the menstrual cycle, she says.

This can be especially helpful for people who experience premenstrual syndrome and those with conditions that can cause heavy bleeding and menstrual pain, such as fibroids or endometriosis.

There are pill and nonpill options for estrogen-containing contraception. When birth control pills contain estrogen, they’re known as combination pills.

Skin patches and vaginal rings also contain estrogen and progestin.

There are pros and cons to each of these, and which you choose will ultimately depend on your:

  • overall health
  • risk of certain health conditions
  • ability to stay on schedule
  • length of time you’d like to prevent pregnancy

Birth control pills don’t actually contain progesterone — they contain a synthetic version of it called progestin.

Some birth control pills contain just progestin (these are called minipills), while others contain progestin and estrogen (these are called combination pills).

Ultimately, which type of hormonal birth control or another contraceptive you opt for will depend on various personal and health factors. Talk with a healthcare professional to figure out the right birth control method for you.

Gabrielle Kassel (she/her) is a queer sex educator and wellness journalist who is committed to helping people feel the best they can in their bodies. In addition to Healthline, her work has appeared in publications such as Shape, Cosmopolitan, Well+Good, Health, Self, Women’s Health, Greatist, and more! In her free time, Gabrielle can be found coaching CrossFit, reviewing pleasure products, hiking with her border collie, or recording episodes of the podcast she co-hosts called Bad In Bed. Follow her on Instagram @Gabriellekassel.