Birth control pills have been the leading method of preventing pregnancy in the United States since their introduction in 1960. They’re effective, readily accessible, and inexpensive. Birth control pills are generally considered safe for most women. They’re not without risks, though.

Newer low-dose birth control pills can reduce that risk. They contain about 20 micrograms (mcg) of estrogen. Estrogen is a hormone that’s in most birth control pills. It’s linked to health risks such as blood clots and stroke. Today’s high-dose birth control pills contain approximately 35 mcg of estrogen. Compare these levels to those of birth control pills in the 1960s, which contained as much as 150 mcg of estrogen.

How do birth control pills work?

Estrogen and progesterone are hormones that signal your body to produce eggs and prepare for pregnancy. If a sperm doesn’t fertilize the egg, the levels of these hormones fall steeply. In response, your uterus sheds the lining that had built up. During your period, your body sheds this lining.

Birth control pills contain either a combination of synthetic estrogen and progestin or progestin alone. Progestin is a man-made hormone that functions like progesterone. These hormones work in different ways to prevent pregnancy.

Estrogen and progestin both prevent the pituitary gland from producing hormones that trigger ovulation. Progestin also thickens your cervical mucus. This makes it harder for sperm to reach any released eggs. Progestin also thins the uterine lining. This makes it harder for an egg to implant there if the sperm fertilizes one.

Learn more: Is It OK to miss a day of birth control? »

Low-dose combination birth control pills

These pills contain estrogen and progestin. When they’re taken correctly, combination birth control pills are up to 99 percent effective in preventing unwanted pregnancy. If you miss a dose, their effectiveness goes down to about 91 percent.

The following may occur if you’re taking a low-dose combination pill:

  • Your periods are likely to be more regular.
  • Your periods may be lighter.
  • Any menstrual cramping you have may be less severe.
  • You may not experience severe premenstrual syndrome.
  • You may have added protection against pelvic inflammatory disease (PID).
  • You may have a reduced risk of ovarian cysts, ovarian cancer, and endometrial cancer.

There are some disadvantages of taking a low-dose combination pill, though. These may include:

  • an increased risk of heart attack
  • an increased risk of stroke
  • an increased risk of blood clots
  • reduced milk production, which is why doctors don’t recommend this pill if you’re breast-feeding
  • spotting between periods

Other side effects may include:

  • nausea
  • vomiting
  • a headache
  • tender breasts
  • weight change
  • depression
  • anxiety

Common brands of low-dose birth control pills are:

  • Apri
  • Aviane
  • Levlen 21
  • Levora
  • Lo/Ovral
  • Ortho-Novum
  • Yasmin
  • Yaz

Low-dose progestin-only birth control pills

The progestin-only pill is often called a “minipill.” This type of birth control is up to 99 percent effective. If you miss a dose, the chance is greater that you will become pregnant than with combination low-dose pills. Although progestin-only pills can produce side effects, particularly bleeding or spotting between periods, the side effects often improve or disappear after a few months. They can also shorten the length of your period.

Progestin-only pills may be a good option for you if you have risk factors that prevent you from taking estrogen, such as smoking or a history of heart disease.

Other advantages of low-dose progestin-only pills include:

  • You can take them if you’re breast-feeding.
  • They reduce your risk of cancer of the lining of the uterus or PID.
  • You may have fewer periods.
  • You may experience less cramping.

The disadvantages of low-dose progestin-only pills can include:

  • greater risk of developing blood clots
  • spotting between periods
  • periods that are more irregular

Other side effects include:

  • bloating
  • weight gain
  • sore breasts
  • headaches
  • depression
  • ovarian cysts

Common brands of progestin-only birth control pills are:

  • Camila
  • Errin
  • Heather
  • Jolivette
  • Micronor
  • Nora-BE

Risk factors to consider

You shouldn’t take birth control pills if you:

  • are pregnant
  • are over age 35 and smoke
  • have a history of heart disease, stroke, or blood clots
  • have a history of cancer of the breast, uterus, cervix, or vagina
  • have a history of migraine with aura
  • have high blood pressure that’s not well-controlled by medication

Are low-dose birth control pills right for you?

If you take your birth control pills at the same time every day, a low-dose or progestin-only birth control pill may be right for you. Progestin-only pills are the only form of oral birth control pills most doctors recommend if you’re breast-feeding.

If you aren’t as diligent about taking your pills at the same time every day, you may find that pills containing 30 to 35 mcg of estrogen are a better option. Talk with your doctor about your health history and your birth control goals. Together, you can select the best birth control option for you. 

Read more: Which birth control is right for you? »