Updated: Feb 14
Written by Kyra Keer, BMSc (Hons), MSc (Master of Physiology and Pharmacology) (c)
Illustrations by Alex McPhail, BA (Hons)
Executive Summary: There are two main types of birth control pills - combination pills and progestin-only pills. The two types differ in the hormones they contain but both are effective at preventing pregnancy in people who ovulate. This post discusses how the different hormones in birth control pills work and why you might choose one pill type over the other.
Hello reader! My name is Kyra, my pronouns are she/her and I reside in the geographical confines of what is currently known as Canada. This post was written on the traditional territory of the Anishinabewaki, Attiwonderonk, & Mississauga First Nations, in what is currently known as London, Ontario. I want to acknowledge my privilege as a white cis-woman, with access to post secondary education, stable healthcare and comfortable housing. My intention is to utilize my education and this platform to help increase awareness of important topics in womxn’s health and to explore social determinants of health and their impact on womxn. I do not intend to speak on behalf of communities that I do not belong to, and I hope to be corrected if my writing is misrepresentative. I am committed to lifelong learning, and continuously educating myself on responsible and effective allyship.
*These sources do not specify the gender identity of the women included. Historical representation leads us to believe that only cisgender women were included.
Birth control (BC) pills are a hormonal option for preventing pregnancy. Other uses for birth control include acne treatment, regulation of periods, and other conditions which involve hormone imbalances (5*). While people use BC pills for a number of reasons, this post will specifically discuss how the hormones in BC pills prevent pregnancy in people who ovulate† and who engage in penile-vaginal intercourse (PVI).
This piece will give an overview of:
It is useful to learn how ovulation works to help understand how BC pills work to prevent pregnancy! Ovulation is a process where your ovaries release an egg into your fallopian tubes – the spot in your body where fertilization can happen to produce pregnancy (1*).
An area in the brain called the hypothalamus produces a hormone called gonadotropin releasing hormone (GnRH). When GnRH is produced, it acts on hormone receptors in the pituitary gland to produce two hormones: follicle stimulating hormone (FSH) and luteinizing hormone (LH). These two hormones act like an ‘on’ switch for the ovaries that helps trigger ovulation (1*).
When you ovulate, your body produces higher levels of estrogen. Estrogen is one of the main sex hormones people who ovulate produce. The other main sex hormone is progesterone. Progesterone and it’s actions on the body can be mimicked by progestin, which is a manufactured hormone used in BC pills (2*). As estrogen builds up in your blood, it acts like an ‘off’ switch for the hormone centers in your brain. This results in the end of an ovulation cycle, and the beginning of your period (1*).
There are two types of BC pills:
The most common BC pill is the combination pill (3*). Combination pills contain both estrogen and progestin. When you take the combination pill, the estrogen in the pill works as a constant ‘off’ switch. It stops GnRH, FSH, and LH from being produced. In most people who ovulate, this prevents ovulation from occurring.
There are three main types of combined pills that are classified based on the ratio of estrogen to progestin in the pill. Monophasic pills contain the same amount of estrogen and progestin in each tablet. Biphasic pills have the same amount of estrogen per tablet, but increased progestin in the second half of the monthly pack’s tablets. Triphasic pills can have varying amounts of estrogen, and the progestin gradually increases in three phases as you complete the monthly pack (4*).
Monophasic, biphasic, and triphasic birth control pills are all similarly effective at preventing pregnancy (4*). The only difference between the three types is the side effects you may experience, which is different for everyone. It is important to self-monitor for any side effects when taking the combination pill and talk about them with your doctor.
For some people who ovulate, taking the combination pill is not recommended. This is because of how estrogen interacts with the liver. The liver has receptors for estrogen which are involved in regulating blood clotting factors. When estrogen binds to these receptors, it causes the liver to produce clotting factors. When you take the combination pill, there are higher-than-normal levels of estrogen circulating in your blood. In some populations of women, this can result in an increased risk of blood clotting and stroke (6*).
Some cases where combination pills should not be taken include (3*):
Over 35 years of age and smoke cigarettes
High blood pressure
History of blood clots
History of stroke
Diagnosed ischemic heart disease
Current breast cancer
Diagnosed liver disease
Diagnosed liver cancer
Migraines with aura
Diabetics who have been diagnosed for 20+ years and/or complications such as nephropathy, retinopathy, or neuropathy
The second type of BC pill is the progestin-only pill, also known as the ‘mini-pill’. This birth control pill is an option for people who ovulate* who cannot take the combination pill or for those who prefer not to take it (4*).
The ‘mini-pill’ works in a different way to prevent pregnancy. The cervix is the point where the vaginal cavity meets the uterus, and it is normally covered in a layer of mucus. The progestin in the mini pill causes the mucus layer to thicken. This makes it difficult for sperm to cross the vaginal cavity into the uterus and fertilize an egg. Even if sperm passes through this barrier, the thickened mucus makes it difficult for sperm to swim into the fallopian tube, where the egg is released during ovulation. Pregnancy is therefore prevented because the sperm cannot reach the egg (4*).
Ultimately, both BC pill types can be effective at preventing pregnancy in womxn who engage in PVI. Learning about the different types of BC pills available can help you advocate for yourself and your sexual health. It is important to identify your personalized needs and concerns, which can help womxn make informed decisions about which BC pill is best, in consultation with a doctor. Always remember that you are in control of your body, and your doctor has a responsibility to help you feel comfortable about the BC option you choose! Don’t be afraid to speak up, ask lots of questions, and stay curious!
†People who ovulate are born with a uterus, ovaries, fallopian tubes, and produce the necessary hormones to undergo ovulation and menstruation.
1. Stanczyk FZ, Archer DF, Bhavnani BR. Ethinyl estradiol and 17B-estradiol in combined oral contraceptives: pharmacokinetics, pharmacodynamics and risk assessment. Contraception [Internet]. 2013 Jun [cited 2021 Jan]; 87(6):706-27. Available from: https://www.sciencedirect.com/science/article/pii/S0010782412010797?casa_token=TehM3u0MhrEAAAAA:iybGQC0yzsqx5DHCJOI0n-HbNRM87Kgua2y6E7LXhWAeWcrvEjWONQzPfGxbrxbBRGZapf5BYm5H
2. Hormone Health Network. Estrogen [Internet]. Hormone.org: Endocrine Society; 2018 [cited 2021 Jan 17]. Available from: https://www.hormone.org/your-health-and-hormones/glands-and-hormones-a-to-z/hormones/estrogen
3.Allan RH. Combined estrogen-progestin oral contraceptives: Patient selection, counseling, and use [Internet]. UpToDate: [Updated 2020 Nov 02; cited 2021 Jan 17]. Available from: https://www.uptodate.com/contents/combined-estrogen-progestin-oral-contraceptives-patient-selection-counseling-and-use
4. Black A, Francoeur D, Rowe T. Canadian Contraception Consensus. J Obstet Gynaecol Can [Internet]. 2004 Mar [cited 2021 Jan]; 26(3):219-54. Available from: https://www.jogc.com/article/S1701-2163(16)30260-2/pdf#:~:text=There%20are%20several%20forms%20of,and%20the%20combined%20monthly%20injectable.
5. Center for Young Women’s Health. Medical Uses of the Birth Control Pill [Internet]. Center for Young Women’s Health: [Updated 2020 Jun 22; cited 2021 Jan 17]. Available from: https://youngwomenshealth.org/2011/10/18/medical-uses-of-the-birth-control-pill/
6. Berg EG. The Chemistry of the Pill. ACS Cent Sci [Internet]. 2015 Mar [cited 2021 Jan]; 1(1):5-7. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4827491/