The Evolution of Birth Control Pills
Owing to their convenience of use and effectiveness, Oral Contraceptive Pills(OCPs) or birth control pills are the most widely used form of hormonal contraception. They act by:
- suppressing ovulation (release of eggs by the ovaries),
- thickening the cervical mucus to prevent sperm from entering, and
- altering the endometrium (tissue lining in the uterus), thus discouraging implantation of the egg.
All of these changes lead to unfavorable conditions for pregnancy to occur.
OCPs available today are usually made up of synthetic versions of estrogen and progesterone (progestin). But this wasn’t always the case.
OCPs have been in use for more than 60 years, and the very first OCP formulations were drastically different from current ones in terms of composition and dosage. Let’s look at a brief history of OCPs - how these were used and how they have evolved over time.
History of oral contraceptive pills
The idea of using hormones for contraception was first suggested in the 1920s when the ovarian hormones, estrogen and progesterone, and their role in reproduction were discovered.
In the 1940s, it was discovered that some plants, like the Mexican yams, contained hormone-like substances.
In the 1950s, synthetic versions of progesterone were developed, known as progestogen or progestin. Clinical trials with a contraceptive could not be done in the United States because dispensing contraception was still a criminal offense at that time. The initial trials, therefore, were carried out in Puerto Rico.
In 1957, the Food and Drug Administration (FDA) approved the use of mestranol (estrogen) + norethynodrel (progestin) for the treatment of menstrual disorders. The first large trial of the combined (containing estrogen and progestogen) OCP took place in 1956-1957, and in 1960 the first combined pill became available in the USA.
The early pills contained as much as 150 µg of estrogen. By the end of the 1960s, a link was found between high levels of estrogen in the pill and the subsequent risk of developing blood clots and stroke. However, by 1973 the first pill to contain only 30 µg of estrogen was developed. New progestogens were also developed that were effective at low doses, and progestogen-only pills (mini-pills) were also produced.
You’d be surprised to know that the complete monthly dose of some modern pills now contains less hormone than a single pill did at the beginning of the 1960s.
Regardless, the invention of birth control pills has been nothing short of revolutionary and it has drastically changed the methods of contraception in the last 60 years.
Benefits of oral contraceptive pills
OCPs are primarily used for birth control and are 99% effective if used perfectly and 91% with typical use. But preventing pregnancy is not the only reason OCPs are used. OCPs are available in many forms and types, and are often used for benefits other than birth control. Some of these are as follows:
- Treating symptoms of PCOS (polycystic ovarian syndrome) such as the absence of periods, acne, and hirsutism (excessive hair on face, chest, and back).
- Endometriosis (presence of the endometrium outside the uterus).
- Adenomyosis (growth of endometrial tissue into the muscular tissue of the uterus).
- Excessive menstrual bleeding (menorrhagia).
- Treating symptoms of PMS (premenstrual syndrome).
- Menstrual migraines.
- Anemia related to menstruation or fibroids (non-cancerous growth in the uterus).
Furthermore, OCPs also show beneficial effects or reduce the risk of endometrial cancer, ovarian cancer, colon cancer, osteoporosis, and pelvic inflammatory disease (PID).
But like almost all medicines out there, OCPs are known to have some side effects. Here are some of the common side effects that one may or may not experience:
- Mood changes
- Breast tenderness
- Vaginal spotting
Also, with prolonged use of estrogen-containing OCPs, there may be an increased risk of blood clots, hypertension, heart diseases, and breast cancer in some women. Therefore, it is important to consult a doctor to assess any risks before starting on birth control pills.
What are the different types of OCPs?
There are many different types of OCPs available, and they differ in their composition, dosage, regimen, and type of hormone(s) used. For convenience and information, we have divided OCPs based on the following parameters:
The three major formulations of oral contraceptives are fixed-dose estrogen-progestin combination (monophasic), phasic estrogen-progestin combination (multiphasic), and progestin-only pills (POPs).
Monophasic pills contain active pills which have the same levels of estrogen and progestin in each of them. These are to be taken for 21 days followed by 7 placebo or iron pills or no pills at all (a pill-free break). These are commonly available in Singapore.
In multiphasic pills, the amounts of estrogen and progestin in active pills vary throughout the 28 days of the cycle. These are further divided into biphasic and triphasic.
Lastly, progestin-only pills (POPs), commonly called the minipill, only use a progestogen or progestin (a synthetic version of progesterone). Each pack of the pills contains low-dose progestin pills and all the pills are active. These are meant to be taken continuously with little or no gap between packs. The progestin dose in a minipill is lower than the progestin dose in any combination pill, therefore it also doesn’t offer as many advantages and choices as monophasic or multiphasic combined oral contraceptive pills. However, they carry fewer side effects.
There are 2 major types of regimens available:
- 21+7 days regimen, where 21 active pills are taken followed by 7 inactive/placebo pills or a 7-day pill-free break
- 24+4 days regimen, where 24 active pills are taken followed by 4 inactive/placebo pills or a 4-day pill-free break.
Almost all OCPs contain one type of estrogen, called Ethinylestradiol. The dosage of this hormone varies from 20 ug to 35 ug. Very high dose of estrogen (>50 ug) is not used for contraception but may be used for abnormal uterine bleeding.
Progestogen or Progestin
Progestin type and dosage varies varies from pill to pill.
Progestins are classified as 1st to 4th generation, based on when they were first available. For example, Norethindrone and ethynodiol are first-gen progestin, levonorgestrel and norgestrel are second-gen, while desogestrel and norgestimate are third, and drospirenone is classified as fourth-gen.
Different generations have some different characteristics. Let’s look at some of the pros and cons of these progestins:
- Norethindrone - Commonly found in monophasic pills, it has been shown to improve cholesterol levels and even help in depression, but does not do anything for acne.
- Ethynodiol diacetate - Has beneficial effects in women with endometriosis. But associated with more frequent spotting or breakthrough bleeding.
- Levonorgestrel - It is the most commonly prescribed progestin contraceptive, and can be used for emergency contraception. However, it is can frequently cause acne.
- Desogestrel - Helps with menstrual cramps, migraines, and weight changes.
- Norgestimate - The progestin of choice for acne due to its low androgenic activity. However, it can often cause weight gain, headaches, and low libido.
- Drospirenone - The only FDA-approved progestin used for premenstrual dysphoric disorder (PMDD).
Thanks to the advances in modern medicine there are many forms of and much safer birth control pill options available now.
If you have any trouble deciding which type of pill is ideal for you, feel free to contact doctors who can help you decide which type of pill is most appropriate for you.
Kasper, D. L., et al. Harrison's principles of internal medicine (20th edition.). New York: McGraw Hill Education., 2018. (pg. 2810-2816)