Plan B is an emergency method of birth control that contains the synthetic hormone levonorgestrel. Women who have unprotected sexual intercourse can help prevent pregnancy by taking this prescription medication within 72 hours after intercourse. This medication works by preventing egg release by the ovaries and interfering with egg fertilization. Plan B can cause menstrual cycle side effects in certain women, which should be discussed with a medical professional if they occur.
Heavy Menstrual Bleeding
In clinical trials for Plan B, nearly one-third of women experienced heavier menstrual bleeding, according to Duramed Pharmaceuticals, a subsidiary of Barr Pharmaceuticals, Inc., the distributor of this emergency contraceptive. Heavy menstrual bleeding can be uncomfortable and may contribute to more frequent or severe menstrual cramping or bloating. Increased menstrual bleeding may require women to change their tampons or pads more often throughout the day. This side effect of Plan B can also increase a woman's risk of developing anemia, a condition characterized by low red blood cell levels. Anemic women can experience dizziness, increased fatigue, pale skin or headache symptoms. Heavy menstrual bleeding typically only occurs during the menstrual period following treatment with Plan B. Women who notice persistently heavy menstrual bleeding for several menstrual cycles after taking Plan B should talk with a doctor for further guidance and care.
Menstrual Cycle Spotting
Nearly 13 percent of women experienced lighter-than-usual vaginal bleeding during the menstrual cycle after taking Plan B during clinical trials, according to RxList. This side effect is often referred to as menstrual spotting and may occur in conjunction with normal menstrual cycle side effects, including abdominal bloating, breast discomfort or headache. An unusually light, irregular or absent menstrual period can be a sign of pregnancy or ovarian problems, and affected women should seek care from a medical professional.
Delayed Menstruation
Nearly 5 percent of women experienced at least a seven-day delay in menstruation as a side effect of Plan B during clinical trials, Duramed Pharmaceuticals reports. Menstruation delay can be a sign of pregnancy, and women who develop this side effect after taking Plan B should contact a doctor.
