I'm so glad to hear that Triphala is working for you people!!! Keep sharing your success stories of what's working, it really helps readers make decisions as to which of my recommendations they should spend their hard-earned cash on. :)
They recommend abstaining from Triphala during menstruation because it causes a downwards movement in energy, and this can cause a heavy menstrual flow. During menstruation, the body naturally wants and produces a downward flow of energy, so adding herbs that do the same thing to CHI will be like overdosing energetically. :)
If you're not taking a high dosage you probably don't need to worry about it, but if you tend to have very heavy flow you may want to take a break.