Plan B Side Effects to the Menstrual Cycle

Accidents happen. Whether you forgot to take your pill, a condom broke or your method of choice malfunctioned, birth control can fail. When that happens, many women turn to Plan B One-Step, a form of emergency contraceptive, to prevent pregnancy. Plan B must be taken orally within 72 hours of birth control failure, according to Plan B's official website. Plan B has been reported to cause temporary changes to a woman's menstrual cycle.

Spotting

• Some women have reported experiencing light spotting one to three days after taking the Plan B One-Step pill. This spotting may be accompanied by symptoms similar to those often accompanying menstruation, such as fatigue, headaches, nausea and abdominal cramping. If you experience severe abdominal cramping, you should contact your physician as soon as possible, according to Plan B's website.

Change in Flow

• After taking Plan B One-Step, your next period may be much lighter or heavier than the usual flow of your periods. The pill sometimes works by changing the lining of the uterus, making it difficult for implantation to occur. The lining of the uterus is what is shed during a menstrual period, meaning a thinner lining would result in a lighter period, while a thicker lining would result in a heavier flow. According to the website RX List, between 12 percent and 13 percent of women who participated in a clinical study reported heavier periods after using Plan B. Twelve percent of the women reported lighter flows, while 75 percent of the women reported little or no change in flow.

Change in Cycle Length

• After taking Plan B One-Step, you may not begin your period on the expected date. Some women have reported starting their periods later than expected, while others have begun their periods earlier than normal. The majority of women begin their periods within one week of their expected start date, according to RX List. Plan B's website recommends that women whose periods are more than one week late after taking Plan B consult their physicians, as pregnancy may be a possibility.