Intermenstrual 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.4
Intermenstrual 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.5
Nausea
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 bedtime can help lower the likelihood of nausea. Anyone experiencing persistent or severe nausea should seek medical guidance.
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
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.4
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