When you take oral contraceptives, the hormone thins out the lining of the uterus making it unable to host egg implantation. The mucus in the cervix thickens, making it tough for sperm to swim through.
Most birth control pills contain 2 hormones, estrogen and progestin. Pills that contain both estrogen and progesterone are called combined contraceptives. There is also another type of pill that contains progestin-only, called the mini-pill.
Progestin-only birth control pills are a popular choice for many nursing and non-nursing women immediately postpartum. This method is less effective than combination pills. However, it is often recommended after delivering your baby because combination pills increase your risk of developing blood clots.
They may also reduce the risk of triggering migraine headaches compared to pills with estrogen.
The same kind of estrogen is in all low dose combination pills. The exact dose of estrogen may have an impact on the kind of side effects you experience.
If you have a history of blood clots, or have high blood pressure, your doctor may advise that you take the progestin-only pill. Also, many organizations are concerned that combined oral contraception may suppress milk production, so they do not recommend them in breastfeeding women. Currently, there is not enough evidence to show that birth control pills affect how much milk your body makes.
Within the family of estrogen-containing pills, there are 2 main types: monophasic and triphasic. As the names suggest, monophasic pills provide the same level of hormones throughout the pill cycle. Triphasic pills also induce a steady state of hormones, but at 3 different levels during the cycle. The 2 types are equally effective for pregnancy prevention.
There are fewer side effects now than there used to be because oral contraceptives today contain a much lower level of estrogen. Lower hormone levels usually mean fewer side effects, but side effects do still occur.
The most common complaint is about breakthrough bleeding. If you are new to the pill or have recently switched types, you should give your body 3 months to adjust.
Some women believe that they will gain weight when taking the pill, but a study reported that the pill has no major effect on weight.
Other possible side effects include headaches (especially migraines), nausea, breast tenderness, and bloating. If the negative side effects last for more than 3 months, talk to your doctor and consider changing brands.
Depending on which kind of birth control pill your doctor prescribes, you could have a pack of 21 pills, 28, or even 90.
If there are 21 pills in the pack, take 1 pill at the same time each day for 21 days. After 7 days of not taking a pill, start a new pack. You will have your period during the break.
If your pack has 28 pills, take 1 pill at the same time each day for 28 days. Since the last 7 pills do not contain hormones, this will be when you will have your period.
Another option is to have 28 pills, but with the final 4 pills being inactive (without hormones). With this kind of pill, your period may be shorter and lighter.
Some pills come in packages of 90 pills (also called continuous-dosing or extended-use). The first 83 pills contain hormones, but the last 7 do not. You will have your period during the 7 days with no hormones every 3 months.
There are also packs with 365 pills. Women take 1 pill a day for a year. Over time, bleeding may become lighter and may even stop.
Taking a week off after 3 weeks of active hormones is part of a normal pill cycle, but skipping days in the middle of the 3 weeks is not a good idea. It could increase your risk for pregnancy.
If you do miss a pill, take it that day as soon as you remember. Or double up (take 2 pills) if you do not remember until the next day. You should use another method of contraception if you forget to take 2 or more pills. Call your doctor or nurse and ask for advice. Complete directions for what to do are also included in the instructions that come with your birth control pills.
You cannot get birth control pills without a prescription, so you have to see a doctor at some point. Be open with your doctor so that you can make the best decision possible about birth control. Women with certain conditions should not take oral contraceptive. Talk to your doctor about any medications you take, as well as any over-the-counter or herbal medications or supplements.
If you experience problems and side effects, speak up. There may be something out there that's better for you.
The American Congress of Obstetricians and Gynecologists
Canadian Women's Health Network
The Society of Obstetricians and Gynaecologists of Canada
Birth control for breastfeeding mothers. Utah Department of Health website. Available at: http://health.utah.gov/mihp/pregnancy/preged/afterpreg/breastfeeding_and_contraception.htm. Accessed March 16, 2016.
Combined hormonal birth control methods: pills, patches, and rings. American College of Obstetricians and Gynecologists website. Available at: http://www.acog.org/~/media/For%20Patients/faq185.pdf?dmc=1&ts=20140519T1146255206. Updated July 2014. Accessed March 16, 2016.
Estrogens, conjugated. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated March 14, 2016. Accessed March 16, 2016.
Oral contraceptives and cancer risk. National Cancer Institute website. Available at: http://www.cancer.gov/about-cancer/causes-prevention/risk/hormones/oral-contraceptives-fact-sheet. Updated March 21, 2012. Accessed March 16, 2016.
11/19/2008 DynaMed's Systematic Literature Surveillance http://www.ebscohost.com/dynamed: Gallo MF, Nanda K, Grimes DA, Lopez LM, Schulz K. 20 µg versus >20 µg estrogen combined oral contraceptives for contraception. Cochrane Database Syst Rev. 2008;(4):CD003989.
4/9/2010 DynaMed's Systematic Literature Surveillance http://www.ebscohost.com/dynamed: Beral V, Hermon C, Kay C, et al. Mortality associated with oral contraceptive use: 25 year follow up of cohort of 46 000 women from Royal College of General Practitioners' oral contraception study. BMJ. 1999;318:96-100.
Hannaford PC, Iversen L, Macfarlane TV, et al. Mortality among contraceptive pill users: cohort evidence from Royal College of General Practitioners' Oral Contraception Study. BMJ. 2010;340:c927.
1/28/2011 DynaMed's Systematic Literature Surveillance http://www.ebscohost.com/dynamed: Truitt S, Fraser A, Gallo M, et al. Combined hormonal versus nonhormonal versus progestin-only contraception in lactation. Cochrane Database Syst Rev. 2010;(12):CD003988.
2/11/2011 DynaMed's Systematic Literature Surveillance http://www.ebscohost.com/dynamed : Dinger J, Minh TD, Buttmann N, Bardenheuer K. Effectiveness of oral contraceptive pills in a large U.S. cohort comparing progestogen and regimen. Obstet Gynecol. 2011;117(1):33-40.
9/30/2011 DynaMed's Systematic Literature Surveillance http://www.ebscohost.com/dynamed: Gallo MF, Nanda K, Grimes DA, Schulz K, Helmerhorst FM. Combination contraceptives: effects on weight. Cochrane Database Syst Rev. 2011;9:CD003987.
Last reviewed March 2016 by Michael Woods, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.