Common side effects include irregular vaginal bleeding, nausea, sore breasts, vaginitis, mood changes, and headache.[4] Rare but serious side effects may include blood clots, toxic shock syndrome, anaphylaxis, gallstones, and liver problems.[4] Use is not recommended in those who both smoke and are over the age of 35.[4] While use in pregnancy is not recommended, such use has not been found to be harmful to the baby.[4] Use during breastfeeding is typically not recommended as it may decrease the milk supply.[4] It mainly works by decreasing gonadotropins thereby stopping ovulation.[4]