I think it's something like 25% of women runners are amenorrheic (don't have their menstrual cycle). I'm one of them. Have been for a long time. Tied up in eating disordered behavior that I'm working to overcome and I know many other women are also trying to do. I'm wondering what other women with this problem have done. Have you modified your diet? Have you experienced any other negative side effects to running besides the usual injuries? (Hair loss?) I'm embarassed to bring this up, since it's not one of the glorious sides of ldrunning. My doctor has usually either said 1. gain weight or 2. take the pill. I've taken the pill, but I'm wondering about the weight issue. It doesn't seem to make a difference whether I gain or not--I don't get my cycle back.