While Plan B is about 75% to 80% effective at preventing pregnancy, there are those times that it does fail. However, because Plan B delivers a dose of the hormone progesterone into your body, it can alter your period. Your next period could come earlier or later than usual.
It is possible that your first pregnancy test was performed too early. Wait another 1 to 2 weeks. If your period still has not begun, repeat the pregnancy test. If it continues to be negative, then you are not pregnant. If you continue to have absent periods over an extended period of time, follow up with your doctor or clinic.
20. March 2012
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