also too much stress can cause a cease of the period, too excessive stress (that happened to me before) over-exercise (track and swim weren't enough to stop mine, darn) and drug addiction.
It may be hard for you guys to understand, it isn't really the blood that is the horrible part, but the way it makes us feel, so icky and blah or grrr. And physically feel like mush. So much for the adjectives LOL
Interesting: the article by ChrisB1 mentioned wild animals not having menstruation. I guess domestic animals might be messed up like human females are: I know dogs bleed, they have those little pads for the dogs during "that time"..
I saw a show once on a women's group that would get together and suction out all the blood from each other all at once so it wouldn't just come out on its own for a few days. I wonder what happened to that idea?