The oral contraceptive pill, commonly referred to as “the pill,” is a form of hormonal contraception taken by women to prevent pregnancy. The pill is a highly effective method of birth control when taken correctly (at the same time daily), with only 0.1% of women experiencing an unintended pregnancy, according to the Association of Reproductive Health Professionals (ARHP); around 1 in 100 women taking the pill experience an unintended pregnancy in the first year of pill use.
However, pregnancy rates increase dramatically in women who miss a pill (rates rise 30-80 times, according to the ARHP).
There are two types of contraceptive pills, both of which contain synthetic forms of the hormones estrogen and progesterone (progestin).
Combination pills contain both of these hormones, whereas the “mini pill” – known as the progestin-only pill – contains only the hormone progestin.
Common side effect of birth control pills include: Inter-menstrual spotting, nausea, breast tenderness, headaches, weight gain, mood changes, missed periods, decreased libido, vaginal discharge and visual changes with contact lenses.
We’ll look at each of these side effects in detail below.
1. Inter-menstrual spotting
Approximately 50% of people using the pill experience vaginal bleeding between expected periods – also known as breakthrough bleeding – most commonly within the first 3 months of starting to take the pill. Generally, this resolves in over 90% of cases by the third pill pack.
During spotting, the pill is still effective as long as it has been taken correctly and no doses were missed. People who experience 5 or more days of bleeding while on active pills or heavy bleeding for 3 or more days should contact a health care professional for advice.
Inter-menstrual spotting may occur due to the uterus adjusting to having a thinner endometrial lining, or maybe due to the body adjusting to having different levels of hormones.
Some people experience mild nausea when first taking the pill, but symptoms usually subside after a short period of time. Taking the pill with food or at the bedtime can help lower likelihood of nausea. Anyone experiencing persistent or severe should seek medical guidance.
3. Breast tenderness
Birth control pills may cause breast enlargement or tenderness. This side effect tends to improve a few weeks after starting the pill, but anyone who finds a lump in the breast or who has persistent pain or tenderness or severe breast pain should seek medical help.
Reducing caffeine and salt intake can decrease breast tenderness, as can wearing a supportive bra.
The sex hormones have an effect on the development of headaches and migraine. Pills with different types and doses of hormone may result in different headache symptoms. Some studies have previously suggested that headaches are least likely to occur with pills that contain low doses of hormones.
Headache symptoms are likely to improve over time. Anyone who experiences new onset of headaches when taking the pill should seek medical attention.
5. Weight gain
Clinical studies have found no consistent association between the use of birth control pills and weight fluctuations. However, many people taking the pill report experiencing some fluid retention, especially in the breast and hip areas.
Fat cells can also be affected by the estrogen in birth control pills, although the hormone causes the cells to become larger rather than more numerous.
6. Mood changes
People with a history of depression are recommended to discuss this with their medical provider, as some people do experience depression or other emotional changes while taking the pill. Anyone experiencing mood changes during pill use should contact their medical provider.4
A study of 90 women published in Human Mapping in 2015 found that use of the birth control pill was associated with smaller cortical thickness measurements in the lateral orbit frontal cortex and the posterior cingulated cortex. These areas of the brain are linked with reward response and evaluating incoming stimuli. However, the study team feels more work needs to be done.
7. Missed periods
There are times when, despite proper pill use, a period may be skipped or missed. Several factors can influence this, such as stress, illness, travel, and hormonal or thyroid abnormalities.
If a period is missed or is very light while on the pill, a pregnancy test is recommended prior to taking the next pack of pills; if further periods are missed or are very light, seek medical advice.
8. Decreased libido
The hormone(s) in the contraceptive pill can affect sex drive (libido) in some people. However, many other factors can contribute to a decrease in libido. If decreased libido persists and is bothersome, this should be discussed with a medical provider.4
In some instances, however, the birth control pill can increase libido. Such an increase may be due to the relief of painful symptoms such as menstrual cramping, premenstrual syndrome, endometriosis and uterine fibroids.
9. Vaginal discharge
Some people experience changes in vaginal discharge when taking the pill. This can range from an increase to a decrease in vaginal lubrication, an alteration in the nature of the discharge, and changes which can affect sexual intercourse. In the event of vaginal lubrication decreasing, added lubrication can be utilized to make sex a more comfortable.
Typically, changes in vaginal discharge are not harmful. Anyone who is concerned about such changes, however, including those who suspect an infection, should speak with their medical provider.