If you are on your period, you might wait before taking this RC as you could experience the worst cramps ever...I imagine this is what childbirth without any painkillers must be like (I've never had a child)...it felt as if someone was ripping out my innards...and this was the third day of my period and I'm not one for having such bad cramps after the first day...some nuprin and 1mg of clonopin eased them after a while...but this was after I spent a good while writhing on the bathroom in pain (I soaked through 2 t-shirts) and on the stairs crying (I've never had cramps so bad I cried)...so again, for me, this stimulates more than caffeine or anything else... next time I'll wait until I am fully off my cycle before taking this!