Guide to the contraceptive pill

There's a lot to take in – but we've done all the hard research for you.
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Team Kin
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Last updated on
May 23, 2024
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Guide To The Contraceptive Pill | Kin Fertility
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Women owe a lot to Margaret Sanger, the pioneer of women’s reproductive rights and founder of the American Birth Control League, the precursor to Planned Parenthood.

In 1951, she convinced Dr Gregory Pincus to develop the first oral contraceptive pill and run the necessary clinical trials. In 1960, the pill was officially approved by the Food and Drug Association (FDA), and from there, it quickly made its way through the Western world, landing on Australian shores in 1961.

Although until 1972, it came with a hefty 27.5% luxury tax and was only available to married ladies. Thankfully, that’s no longer the case and around 27-34% of Australian women claim the birth control pill as their go-to for contraception [1][2].

You may know that the pill is 99% effective at preventing unwanted pregnancy (when used correctly), but there is a lot more to learn about this magical little pill [3]. So first things first, what is the contraceptive pill and how exactly does it work?

How does the birth control pill work?

The short answer is that it stops you from ovulating. If you don’t ovulate, there’s no mature egg released and simply put, no egg = no chance of getting pregnant.

Birth control pills work by synthetically keeping the levels of oestrogen and progesterone equal at all times.

This stops the pituitary gland in your brain from sending signals that release the 2 hormones that trigger ovulation: the follicle-stimulating hormone, which signals the growth and maturation of ovarian follicles, and the luteinizing hormone, which prepares a mature egg follicle to burst and release the egg.

In addition to this, the pill also helps to prevent pregnancy by changing the consistency of your cervical mucus, making it harder for sperm to get through.

What are the types of birth control pills?

There are 2 versions of the pill to choose from, and they work in different ways.

The combined pill

This is the OG birth control pill and the one that most people are referring to when they talk about “the pill”. The combined oral contraceptive pill is made using both oestrogen and progestin, which works to prevent pregnancy in 3 ways:

  • It prevents ovulation. Remember, no egg, no chance of pregnancy.
  • It thins the lining of your uterus, essentially making it an environment incapable of nurturing a fertilised egg (if one were to exist).
  • It thickens your cervical mucus, creating a barrier between your uterus and sperm, which makes it nearly impossible for the little swimmers to pass your cervix.

The mini pill

The mini pill contains progestin only and is great for women who may not be suited to be exposed to additional oestrogen.

It’s also commonly recommended for breastfeeding mothers as some studies have shown that oestrogen can interfere with the lactation process.

Progestin is a synthetic form of the hormone progesterone, which is produced after ovulation by the corpus luteum — the discarded follicle sac of your mature egg — in a regularly ovulating body. Its purpose is to support the development of the endometrium (uterine wall) to make it suitable to host a fertilised egg (embryo).

However, when progestin is present at high levels, it not only prevents the body from ovulating, it actually regulates the uterine wall, preventing it from getting too thick. Given a growing egg needs a thick, cushy uterine wall to grow in, there are no chances of implantation here.

The other thing to note is that the mini pill consists of only active pills, meaning there are no placebo or inactive pills in the pack. As such, there will generally be an absence of the actual period, though the lack of oestrogen can allow for some breakthrough bleeding to occur, especially if you miss a pill, even by a few hours.

Does the pill make you skip your period?

One of the major draw-cards of taking birth control is the ability to forego that monthly ritual of letting it flow — but is it safe to skip your period?

In short, yes. But the truth is, it really depends on your individual body.

There are heaps of reasons you may want to skip your period, which can range from serious medical conditions like endometriosis and dysmenorrhea to more practical reasons, like the beach holiday you’ve planned.

For many women, like active-duty military, who work in environments with limited access to clean bathrooms, the ability to control menstruation at work is not just convenient, it’s often necessary.

Plus, severe menstrual symptoms like excruciating pain caused by endometriosis, intense mood disorders caused by premenstrual dysphoric disorder (PMDD), and menstrual migraines don’t get activated when you skip your period, so the benefits of the pill can reach far beyond convenience.

Does anything make the pill less effective?

Yeah, she’s tough, but there are still a few watch-outs when it comes to the effectiveness of your pill.


Some medications can reduce the pill’s effectiveness by increasing the metabolisation of hormones.

Specifically, one study showed that consistent use of antibiotics such as rifampicin and rifabutin, drugs used to treat tuberculosis and meningitis, and a selection of anticonvulsants can prevent the pill from suppressing ovulation [5].

These drugs increase enzymes in your body, which can interfere with the processes of oral contraception. Others include [6]:

  • Anti-fungal drugs
  • Certain drugs used to prevent seizures
  • HIV medications

Even though there is limited research on the interference of these medications with birth control, it’s best to exercise caution if you’re taking anything that may put you at risk. Use a backup method of birth control throughout the course of your treatment and for at least 1 week after.


Most supplements have no effect on contraception, but a select few herbs, extracts, and other natural supplements can make it less effective by decreasing absorption or interfering with the breakdown of the hormones.

The supplements listed below have raised concerns about causing interference with the pill. If you’re taking any of these or additional herbal supplements, be sure to read the packaging carefully, speak to your pharmacist about the potential impact, and always use a backup form of contraception if you’re unsure.

  • Flaxseed [7]
  • Saw Palmetto [8]
  • Garlic pills [9]
  • Alfalfa [10]
  • St. John's Wort [11]

All of these supplements are best avoided if you use the pill as your only form of birth control. If you accidentally take any of the supplements listed above, it’s best to use condoms or another secondary form of birth control to reduce your risk of pregnancy.

Digestive disorders

Your body needs to fully absorb each and every birth control pill you take in order to stop you from becoming pregnant. If you have a digestive or autoimmune disorder like Crohn’s disease, Coeliac disease, or IBS, it could make the pill less effective.

Temporary digestive issues such as vomiting or diarrhoea also have the potential to make the pill less effective, so it’s important to use a second form of birth control, such as condoms if you experience acute diarrhoea that lasts for longer than 24 hours at a time.


A healthy BMI range in Australia is considered to be anything between 18.5-24.9. If your BMI places you in the overweight or obese range, you have a higher risk of becoming pregnant while using contraception than women who have a lower BMI.

Researchers have actually found that women with a BMI of 27.3 or higher had a 60% higher risk of becoming pregnant while using the birth control pill than women with a BMI that ranked in the mildly overweight category or lower [12].

Plus, women with a BMI higher than 32.2 have a more than 100% higher risk of becoming pregnant while using contraception.

In general, the effectiveness of contraception decreases as your weight and BMI increase.

What to do if you miss a pill

It’s important to take your pill at the same time every day for the best results and effectiveness. Its effectiveness drops to about 91% when factoring in human error, like missed pills or inconsistency in the time of day you take the pill, meaning it's still possible for you to get pregnant [13].

But life gets in the way.

If you miss a pill, take it as soon as possible (even if this means taking 2 pills on the same day). If you miss more than 1 pill, take the missed pill as soon as you remember but ensure you’re using a backup form of contraception until you’ve taken 7 hormone pills in a row. You may also want to consider getting your hands on the morning after pill.

Always refer to the instructions on the packaging of your specific pill to ensure you’re following the best procedure and are protected.

Oh, and another quick note: if you miss a sugar pill, there’s no need for concern.

In fact, some packs don’t even have sugar pills. Sugar pills contain no hormones and serve the purpose of only keeping you in the habit of taking the daily pill so that you stay on track when it comes time to start a new hormonal pill pack.

What if you miss a mini pill?

Then, the above advice doesn't apply. If you’re taking the mini pill, your contraception has lower levels of hormones, meaning if you miss it by even 3 hours it may reduce the effectiveness [14].

It’s absolutely necessary to use a backup form of contraception for at least 2 days if you miss 1 of your mini pills.

Common side effects of the pill

There is a range of potential contraceptive pill side effects. The good news is, for the most part, they aren’t incredibly serious and should subside after your body adjusts, usually within a month.

Breakthrough bleeding

Some women experience breakthrough bleeding during their cycle if they choose low-dose pills or mini pills. Similar to what happens when taking the sugar pills in your pack, the lower dosage or lack of oestrogen can trigger the body to release the uterine wall and cause spotting.

Weight gain

Perhaps one of the most common concerns when making the decision to go on the pill is weight gain. It’s not unheard of to put on weight during your period and lose it just as quickly, but there's actually no link between weight gain and oral contraceptives [15].

What there is, however, is a link between increased levels of oestrogen and fluid retention [16].

Medically, this is known as premenstrual fluid retention and it occurs naturally in your cycle as hormones fluctuate and oestrogen and progesterone levels rise. Combined oral contraceptive pills can cause oestrogen levels to be anywhere from 6-10 times higher than normal, so naturally, fluid retention can be triggered.

If you notice a rapid increase on the scale within the first few weeks of taking the pill, without any major changes to diet and exercise, it’s most likely fluid. As you maintain your normal health habits, you’ll notice your body will adjust and you’ll gradually make your way back toward the norm.

Breast tenderness

Again, similarly to what happens naturally during your cycle when your hormone levels increase, the pill can stimulate breast tissue, resulting in anything from mild discomfort to enlarged breasts.

However, know your boobs, ladies! Keep tabs on anything that feels out of the ordinary and when in doubt, see your doctor.


While it may occur when you first start taking the pill, nausea is more commonly a result of emergency contraceptive use than regular birth control.

Lower sex drive

The pill reduces the levels of androgens in your system, so it can lower your sex drive, with about 15% of women reporting changes to their libido [18].

Testosterone is the major androgen associated with sexual urges, and your body naturally increases its production during ovulation to encourage frisky business at prime fertilisation time.

We’re not only not ovulating when taking the pill, but the increased levels of female sex hormones hinder the production of testosterone [19]. You get the picture.

Less common, more serious side effects

There are some less common, albeit more serious, side effects involved with the pill. Similarly to the above, the majority should subside. However, if any of these symptoms persist or really strike you as out of the ordinary, speak to your doctor ASAP.

Headaches and migraines

Increased risk of headaches and migraines is more common in users of combination pills, so if you’re already susceptible, choosing the mini pill or a lower dose combined pill may be best.

Migraine headaches affect 24% of women of reproductive age and can be completely debilitating [20]. They can last from hours to days, are characterised by severe pain and throbbing, and can be accompanied by nausea, vomiting, and extreme sensitivity to light.

If you begin suffering migraines after starting birth control, speak to your doctor immediately as it may signal an increased risk of stroke and it’s best to seek an alternative contraceptive option.

Mood changes

Truthfully, the links between oral contraceptives and mood changes are understudied.

However, one particularly oft-cited study in Denmark has shown links between increased hormone levels (particularly progesterone) and depression. This is also why during a normal cycle you experience symptoms of PMS when progesterone levels are on the rise [21].

Keeping in mind that your levels are elevated continuously whilst using contraceptives, there is a slightly higher chance to experience feelings of depression, anxiety or fear, with about 4-10% of women reporting negative changes to their mood [22].

Blood clots and deep vein thrombosis (DVT)

The FDA has reviewed a selection of studies identifying an increased risk of developing blood clots, including DVT, in women taking birth control pills containing progestin. The FDA found the risk at about 3-5 times higher than the average healthy, non-pregnant, non-birth-control-taking woman [25].

That may sound pretty scary, but to put this into perspective, the risk of developing blood clots during pregnancy is 5-20 times higher than the average woman, and even more so in postpartum [26].

For new mothers particularly, using combination birth control pills is not recommended within 3 weeks of delivery, as your risk of DVT is heightened immediately after childbirth.

While oestrogen has been linked to an increase in blood clots, the risk is actually considerably low assuming you’re not predisposed to their development. If you are, it’s extremely important to have a conversation with your doctor about the best possible contraceptive solution for you.

You may be predisposed to blood clots if you’ve had surgery, trauma to the body or brain, pregnancy, hormonal therapy or are immobile.

Blood clots can also be genetic, so getting a good grasp of your family health history is important. If you have previously had any blood clots, or are aware of any family history of blood clots, it’s extremely important this is brought up with your doctor. It may not be appropriate for you to be on the combined pill and alternative options should be discussed.


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