Amphetamines (including MDMA) commonly disrupt the menstrual cycle. Often this implies inducing the period early (so you get your period right after rolling/tweaking/etc), and if you are rolling/tweaking/whatever a LOT, this can eventually lead to fewer periods or no periods, especially if you are not eatin, are exercising more, and losing weight...
My period is almost always brought on by using meth, and sometimes (though rarely) by rolling. This is relatively normal -- only if your periods are stopping altogether, or you are bleeding multiple times a month, should you worry.
How frequently do you roll, and what other drugs do you use? Are you eating and sleeping enough? Are you a normal weight? If not, you should consider taking a break or rolling less frequently.
[This message has been edited by fairnymph (edited 09 October 2001).]