How does birth control work?

How does birth control work?

Birth control or contraception is a safe and easy way to prevent pregnancies. There are over twelve forms of birth cont

Birth control or contraception is a safe and easy way to prevent pregnancies. There are over twelve forms of birth control broadly classified as barrier methods, short-acting hormonal methods, long-acting hormonal methods, fertility awareness methods, and sterilization. Contraceptive methods work by preventing sperm from reaching the ovum or preventing implantation. 

How do birth control pills work? 

Birth control pills are a modern form of short-acting hormonal contraception that prevents pregnancies. Pills contain synthetic forms of hormones such as estrogen or progestin. When you take these pills, they create changes in your body that prevent pregnancy such as: 

  • Thickening cervical mucus, making it difficult for the sperm to pass through and fertilize the ovum
  • Preventing ovulation
  • Changing the lining of the uterus so that the embryo doesn't get implanted. 

Types of Birth Control Pills 

There are several hormonal birth control pills available in Canada but they fall under two categories:


Combination pills

Combination pills also called combined oral contraceptives or simply 'the pill', are pills that contain synthetic forms of the hormones estrogen and progestin. In each pack, there are active pills and inactive pills. The active pill contains hormones and the inactive pill doesn't. The hormones in the active pills create changes in your body that prevent pregnancy. In contrast, the pills without hormones reduce hormone levels to allow bleeding, mimicking the natural menstrual cycle. Some inactive pills contain low-dose hormones, iron, and vitamins. While taking combination birth control, you can expect your period while taking inactive pills. There are various types of combination pills such as: 

  • Monophasic pills: Monophasic combination pills are used in one-month cycles. The active pills contain the same dose of estrogen and progestin. The inactive pills are taken during the last week of the cycle resulting in a period.
  • Multiphasic pills: These are similar to monophasic pills but the active pill provides different levels of hormones during the cycle. Inactive pills are taken during the last week of the cycle resulting in a period. 
  • Extended cycle pills: These pills are used in 13-week cycles. The active pills are taken for 12-weeks, and the inactive pills are taken during the 13th week. Taking the inactive pills causes you to have your period. This means you will have your period three to four times a year while taking this pill.

Pros and cons of combination pills 

Every form of contraception has its benefits and drawbacks; the combination pill is no exception. It is important to know the pros and cons of taking the combined oral pill to help you decide if it is the best form of contraception for you.


  • Combined oral pills are very effective. When taking the pill properly, there is only a 1% chance you will get pregnant. 
  • They also work round the clock, so there is no need to interrupt periods of intimacy to get contraceptives. 
  • Their effects are easily reversible. That means if you change your mind about preventing pregnancy and stop taking them, you can get pregnant right away. 

You can also look forward to many positive health effects while taking the pill due to their estrogen content, such as:  

  • Clearer skin and reduced acne
  • Regular, lighter, less painful periods 
  • Reduced risk of ectopic pregnancy
  • Some protection against thinning bones
  • Reduced premenstrual syndrome symptoms
  • Lower risk of cancers of the colon, womb, and ovaries
  • Some protection against pelvic inflammatory disease 
  • Lower risk of non-cancerous breast disease, fibroids and ovarian cysts


  • While combination pills have several positive effects, some women experience increased health risks due to the estrogen content, including:
  • Temporary side effects such as nausea, headaches, breast tenderness, and mood swings.
  • Increased blood pressure 
  • Breakthrough bleeding and spotting. This is common during the first few months 
  • A higher risk of blood clots and breast cancer

Some popular combination pill brands are: 

  • Aleese 
  • Alysena
  • Apri
  • Aviane
  • Loestrin
  • Indayo
  • Mirvala
  • Azurette
  • Beyax
  • Enpresse
  • Estrostep Fe
  • Karina
  • Loestrin
  • Low-Ogestrel
  • Natazia
  • Ocella
  • Ortho-Novum
  • Ortho Tri-Cyclen
  • Seasonable
  • Seasonique
  • Velivet
  • Yasmin
  • Yaz

Mini pills

Mini pills, also called progestin only pills are another form of oral contraceptives. They contain only one type of synthetic hormone— progestin. They are a good choice for women who want to prevent pregnancy but can't take estrogen. The progestin only pill works by thickening cervical mucus and preventing ovulation. All Mini pills are active and you may or may not have a period while taking them.

Pros and cons of Mini pills.

There are several pros and cons of taking the Mini pill. Some of them are:


  • They ease premenstrual tension
  • They can be used by women who smoke
  • They have fewer side effects compared to combined pills 
  • They are ideal for breastfeeding women because they do not reduce breast milk production 
  • They do not raise blood pressure or increase the risk of cardiovascular disease
  • Can be used by women who have had deep vein thrombosis 


  • Weight gain
  • Breakthrough bleeding and spotting may occur 
  • They may be ineffective for women who weigh more than 70kg
  • They may be ineffective if the pills are not taken at the same time every day. 
  • Slightly increased risk of heart attacks, blood clots, stroke, and breast cancer
  • Side effects such as nausea, low sex drive, breast tenderness, headaches, acne, and depression 

Some common Mini pills brands include:

  • Camila
  • Erin 
  • Heather 
  • Jencycla
  • Movisse
  • Nor-QD
  • Ortho Micronor

How should I use birth control pills?

You use birth control pills by following the instructions on the pack. Combination pills come in many formats, such as a monthly pack which can follow 21-day, 24-day, or 28-day cycles, or an extended cycle pack which can follow 91-day cycles. For all of these pill types, you need to take your pill every day. 

Mini pills come in a pack of 28. You need to take a pill within the same three-hour window every day.

Who can take birth control pills? 

Most women can safely take birth control pills. However, for some women, oral contraceptive pills are not recommended. Obstetricians and gynecologists do not recommend this form of birth control for women above 35 years who smoke or women who have had any of these health conditions:

  • Lupus 
  • Diabetes
  • Blood clots 
  • Liver disease
  • Migraines with aura
  • Stroke or heart disease 
  • Unexplained vaginal bleeding 
  • Uncontrolled high blood pressure 
  • Smoke and have hypertension 
  • Cancer of the breast, uterus, cervix, or vagina
  • Plan to have surgery and prolonged bed rest

Deciding on the birth control pill to use

The birth control pill you use has to be effective and safe for you. Even if you do not have any of the health and lifestyle conditions mentioned earlier, you still need to consider a few things before choosing a pill. To make the best choice, talk to your doctor about your contraceptive plans. Some additional factors to think about before choosing a birth control pill include: 

  • Your weight 
  • If you are breastfeeding 
  • Your cardiovascular health 
  • Any medications you are taking 
  • The nature of your menstrual periods 
  • Any chronic health conditions you have 

How effective are birth control pills? 

According to Planned Parenthood, used perfectly, birth control pills are 99% effective at preventing pregnancy. But human errors abound, reducing the actual effectiveness of the pill to 91%. In practical terms, this means that if 100 women are on birth control pills for a year, nine will become pregnant. However, pills are more effective than fertility awareness methods where if 100 women use them for a year, 12 to 24 of them will become pregnant. If you want a more effective, reversible contraceptive method, you can consider another hormonal birth control method such as implants or the intrauterine device. 

Factors that can make birth control pills less effective

Several factors can reduce the effectiveness of a hormonal contraceptive such as the birth control pill. These factors prevent your body from getting the right amount of estrogen or progestin to prevent pregnancy. Some of them are:

Inconsistent timing  

You have to take the pill every day for it to work. Also, progestin only pills have to be taken within the same three-hour window every day to be effective. Mistiming or missing your pill makes it less effective. If you have missed a pill or missed the timing, then you should follow the instructions on the pack. If you miss your pill for two days in a row, you should use a backup method of contraception such as a condom until you have completed  21-days of pills correctly. 


Medication taken for other health conditions can reduce the effectiveness of your birth control pills. The drugs used to treat the following health conditions reduce the effectiveness of the pill: 

  • Depression, e.g sertraline (Zoloft)
  • Epilepsy e.g. phenytoin, phenobarbital, felbamate, primidone , topiramate, carbamazepine and oxcarbazepine
  • Fungal infections e.g ketoconazole and griseofulvin
  • Narcolepsy e.g. modafinil
  • HIV eg darunavir (Prezista), nevirapine (Viramune), efavirenz (Sustiva), lopinavir/ritonavir (Kaletra)
  • Tuberculosis e.g rifampicin
  • Other medications such as hypertension-lowering and cholesterol-lowering drugs

If you are taking any of these medications, talk to your doctor before taking any hormonal contraceptives.

Dietary supplements 

Dietary supplements are commonly taken to boost health. Most can be taken alongside birth control pills but a few of them reduce the effectiveness of birth control pills and should be discontinued. These include: 

  • St John's wort
  • Alfalfa
  • Garlic 
  • Flaxseed 
  • Saw palmetto

Seek medical advice to ensure your dietary supplements will not affect your contraceptives.


Birth control pills work less effectively in overweight women or those with obesity. If your Body Mass Index (BMI) places you in the overweight or obese category, your risk of becoming pregnant on birth control pills is higher than women in the normal BMI range. Birth control pills use the one-size-fits-all dosing model, which is not as effective for larger bodies. The more a woman weighs, the less effective birth control pills will be for her. If you are overweight or obese, talk to your doctor about an alternative form of birth control. 

Some disease conditions 

For oral contraceptives to work optimally, they must be absorbed through the digestive tract. Any disease condition that hinders absorption can reduce the effectiveness of birth control pills. Therefore, health conditions like Celiac disease, Crohn's disease, or irritable bowel syndrome (IBS) can make the pill less effective. Taking oral contraception if you have any of these health conditions creates an increased risk of pregnancy. Instead, you should talk to your doctor to get advice on the best contraceptive to use. Also, if you experience acute diarrhea or repeated vomiting that lasts for up to 24 hours while on the pill, this increases your pregnancy risk and you should use a backup method of contraception. 

How to get birth control pills in Canada?

You need a doctor's prescription to get contraceptive pills in Canada. Your doctor will help you chose an oral contraceptive with the least risks and the most health benefits for you. Your doctor will also follow up to make sure you don't develop any severe side effects. You can get a birth control prescription from:

  • Walk-in clinics
  • Your family doctor
  • Sexual health clinics
  • Online doctor's consultation

How long does it take a birth control pill to work? 

Some forms of contraception, like barrier methods, work instantly, while some methods like a vasectomy, take up to three months. Birth control pills take 1-7 days to work depending on the type of pill, the phase of your cycle, and if you have recently had a baby or lost/terminated a pregnancy.  The specific times are as follows:

Progestin only Pills

If taken within the first five days of your menstrual cycle, progestin only pills work immediately.  If you have a  cycle that is less than 28-days long or if you start taking them after the fifth day of your cycle, progestin only pills can take up to two days to start working.  You can take them 21 days after delivery, and they will start working immediately. If they are taken within five days of pregnancy loss or termination, they start working at once. If taken after that, they begin to work after two days. 

Combination Pills

If you take combination pills during the first five days of your cycle, they become effective immediately. If taken after the fifth day, they take seven days to work. They can be taken on the 21st day after delivery with instant effects. In pregnancy loss or termination, they are immediately effective at preventing pregnancy if taken within the first five days. If taken later than that, they become effective after seven days. The trimester of the pregnancy might affect the pill's effectiveness, so it is best to seek medical advice. 

When should I seek medical attention while taking birth control pills?

Birth control pills can cause some unwanted side effects, especially when you first start taking them. Some of the side facts are minor and are likely to wane with time. Common minor side effects include: 

  • Nausea
  • Sore or swollen breasts
  • Small amounts of menstrual bleeding, or spotting, between periods
  • Mood changes
  • Mild headache

Apart from these, there are some side effects that are more serious and require immediate medical attention. Some of them include: 

  • Abdominal pain (belly pains)
  • Chest pain 
  • Headache (severe)
  • Eye problems (blurred vision)
  • Swelling or aching in the legs and thighs 

These side effects can be remembered using the acronym ACHES and require urgent medical attention. They might be signs of gallbladder disease, heart disease, stroke, high blood pressure, or blood clots. 


Birth control pills protect against pregnancies when taken properly. They also have significant benefits and drawbacks. Seek medical advice to help you choose the best contraceptives for you. Remember that certain supplements and medications can reduce the effectiveness of oral contraceptive pills and increase your pregnancy risk. Get urgent medical attention if you notice any of the severe side effects. If you have any doubts about how effective your birth control pill is, use a backup method of contraception such as a condom and seek medical advice.

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