Hi, Lo Loestrin Fe contains both ethinyl estradiol as estrogen and norethindrone as progesterone which is used to prevent unwanted pregnancies from unprotected sexual intercourses by preventing the release of an egg during the menstrual cycle. Lo Loestrin Fe contains both estrogen as well as progesterone and it works by introducing these hormones into your system. For that reason, your regular menstrual periods may become changed or irregular. Women using Lo Loestrin Fe may experience lighter bleeding, irregular periods or skip their periods entirely. Some women may also suffer from spotting or breakthrough bleeding between menstrual periods, especially at the first phase of treatment with Lo Loestrin Fe. These side effects are mild as well as self limiting and will go away eventually over time as your body adjusts to this medication. But, if these side effects persist for long or bother you, then you should inform your doctor first for medical help. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Zubayer Alam, General And Family Physician