I don't know for sure, but I had a bad reaction to it, and had a six month long period after I got the shot. The doctor started giving me a shot once a week, trying to get it to stop, but finally just letting it to wear out worked the best. So if you are having a long period, contact your doctor, s/he will tell you if it is normal and needs to be a concern. Most doctors offices have awesome nurses that are willing to give you simple answers. My reaction was very uncommon, but not unlikely. Some people can take it better than others.