Got Questions About How Hormonal Birth Control Works? We've Got Answers

Photo: Leandro Crespi

At mindbodygreen, we value a natural approach to health—and that includes women’s health, hormone health, and reproductive health. We talk a lot about the pill with our collective of doctors and experts in integrative and functional medicine urging those looking to prevent pregnancy—and those suffering from hormone imbalances, painful periods, acne, or even conditions like PCOS—to try other options before turning to artificial hormones. That said, we know that what’s right for one person isn’t right for everyone. If you decide that this form of contraceptive is the right choice for you, it’s important to know exactly how it works. 

Oral contraceptive pills are one of the most commonly used forms of birth control, with about 15.9 percent of women ages 15 to 44 in the United States currently taking the pill. But how does this method of birth control really work—and how effective is it? Let's dive in.

What's in the pill?

The most commonly used birth control pills contain a combination of two synthetic hormones: estrogen and progestin. These are referred to as combination or combo pills, and the ratio of estrogen to progestin varies based on brand. (There are progestin-only pills, too, but those are less common.) Combo pills prevent ovulation—when the egg is released from the ovary—from occurring because the estrogen and progestin signal the brain to slow down the release of the follicle-stimulating hormone and luteinizing hormone, the hormones that direct the ovary to mature and release an egg.

At the same time, the pill also makes it harder for sperm to fertilize an egg. For example, it can thicken the cervical mucus, which prevents sperm from swimming up to the egg.

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How effective is it, really?

When you first start taking the pill, it can take up to seven days for it to be effective depending on where you are in your cycle, so you need to use another form of protection during that time.The birth control pill is typically very effective, with only a 1 percent failure rate—but that's only if it's used perfectly and taken every day. Considering many people will accidentally miss a day here and there, the CDC estimates that its "typical use" failure rate is closer to 9 percent. In comparison, the "typical use" failure rate for the IUD and condoms are 1% and 15%, respectively. The rhythm method which involves calculating the "fertile window" by tracking the length of cycles, and thus predicting the which days to avoid having sex has a failure rate of 25%. With mobile apps, women are better able to track their cycles and a new app called Natural Cycles, which uses tracking and daily basal body temperatures was just approved by the FDA with a failure rate of 7.4%. However, any approach using tracking methods can only work for women who have regular cycles.

If you forget to take a pill one day, you can make it up the next day by taking two pills and probably be OK. But forgetting to take the pill for one or more days without realizing it—and then making up for it—is the most common issue that leads to pregnancy. If this happens, you should be using a backup method of birth control. The birth control pill can be less effective for women who are severely overweight and have a BMI greater than 35. There are also several medications that can make the birth control pill less effective, such as certain anti-seizure medications, HIV medications, and certain natural remedies like St. John's wort.

Photo: @crankyT

Do you need to have a period while on the pill?

Most pills are organized in a 28-day pack, with three weeks of hormones and one week of hormone-free placebo pills. Because the placebo pills don’t contain any hormone, you don’t need to take them—though sometimes they do contain useful supplements like iron, folic acid, or other vitamins as the pill may put you at risk for multiple vitamin and mineral deficiencies, including various B vitamins and magnesium. The main reason the placebo pills are included in the pack is to keep you in the habit of taking the pill every day and preventing you from forgetting when to start the new pack of pills.

The week without hormones allows the lining of the uterus to shed, which is your period. However, there is no medical reason you need to shed the lining of the uterus once a month while on the pill, even if you have a pre-existing condition like PCOS. For example, since women who have PCOS don't have regular periods, they run a higher risk of developing uterine cancer. But since the pill reduces the risk of an overgrowth of the uterine lining, it has been shown to help protect them, whether or not it makes their periods more regular.

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Do you have to take it at the exact same time every day?

The good news is that the pill does not need to be taken at the same time every day. But it will make it way easier to remember to take the pill every day if you pick a time that generally works for you and you stick with it. If you are not good at taking a pill every day, even with all the great apps that can give you reminders, then maybe you should explore another form of birth control like an IUD, implant, or long-term injections.

What are the benefits and side effects of being on the pill?

The birth control pill often makes your periods lighter and shorter and sometimes they get rid of periods altogether. Some women also report that being on the pill improves complexion and decreases the incidence of cysts in the ovaries or breasts.

The most common complaints when starting the pill are breast tenderness, nausea, headaches, and irregular light bleeding (what we all commonly refer to as spotting). All of these symptoms, if they occur, will likely entirely go away or decrease significantly within a few months. If you're concerned about these side effects, you can also talk to your doctor about switching to another brand or a different form of birth control. Some integrative and functional medicine doctors postulate that the pill may affect gut health, mood, and libido.

The amount of estrogen in the pill can affect its side effects: Lower doses of estrogen are more likely to cause breakthrough bleeding, and higher doses of estrogen are more likely to cause nausea. It is reasonable to opt for either the higher- or lower-dose estrogen pills. It depends on what potential side effects bother you more. Whatever the amount of estrogen there is, it stays the same all cycle, (except for the placebo week!) in most formulations.

The type of progestin matters, too. There are eight different progestins that are used in different formulations of the pill. The amount and type of progestin will vary, which can modulate your risk of a blood clot (though that risk is low) and influence the unwanted side effects of oily skin or acne, as well as other side effects. The progestins are usually present at the same dose throughout the cycle, too, but there are some pills in which the progestins increase each week throughout the cycle.

Photo: @Toeps

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Is it bad to take synthetic hormones?

Sometimes women assume natural hormones are better than synthetic hormones, but it's important to remember that even bioidentical hormones—which are considered "natural" because they are plant-based and are molecularly identical to your natural hormones—are synthesized in a lab. (These biogenetical hormones are often used to treat symptoms of menopause.) But how a hormone is made is only one aspect that contributes to the risk of taking a hormone. Much like supplements, these "natural" hormones aren’t strictly regulated by the FDA so inconsistent dosages, safety, and efficacy are all concerns. It is one thing to take natural hormones to minimize hot flashes; in this case, if it doesn’t work, you are just uncomfortable because your hot flashes are still happening. However, if you are trying to prevent a pregnancy, you need to make sure that the right amount of hormone is being taken that will effectively prevent a pregnancy and be safe to take.

What are the risks of being on the pill?

Though many women don't have complications when taking the pill, there are some risks that you need to be aware of. If you smoke, you should not take the pill past the age of 35, as it will increase your risk of having a stroke. And if you have any of the following conditions, you should not be using oral contraceptives for birth control: migraines with aura, high blood pressure, uncontrolled diabetes, and history of blood clots, breast cancer, heart attacks, strokes, or liver disease. As mentioned before, the pill decreases your risk for certain types of cancer, but they may increase in depression and breast cancer risk. If you are breastfeeding, taking oral contraceptive with estrogen and progesterone may decrease your milk supply, so you should consider a progestin-only pill.

How do pills affect fertility?

So far research suggests that the pill has not been found to decrease fertility, so it shouldn't affect your ability to have a baby in the future. When you are ready to start trying to have a baby, you stop the pill and your regular menstrual cycle should resume. Occasionally, it may take a little longer for your body to rebound, and there could be a delay of a few months (or potentially even longer) before your regular cycle starts back up again. It's also important to remember that the pill is not a cure for disease like PCOS (though it does help diminish symptoms like acne, hair growth, and painful periods) that can affect fertility. When you go off the pill, the issue will still be there. If you are considering egg-freezing, it is very common for physicians to have you stop taking the pill for several months before the egg-freezing to maximize the chance of success.

Considering an IUD? Here's what you need to know.

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