The oral contraceptive pill is the most researched product in the history of modern medicine, and its safety has long been established. Some women may experience side effects such as nausea, vomiting, chloasma (melasma), skin or hair changes, headache, water retention, slight weight change, breast tenderness, and changes in libido. Menstrual irregularities such as spotting, breakthrough bleeding or amenorrhea can occur during its use.