It Just depends. I used only 1, 10mg vial and In Only 8 days was darker then Ive ever been! I had a good tan already though and was Working in the sun everyday and also Tanning huts each of those days.
Stuff is Crazy, there was no wondering if it was working. It almost worked to good.... Only downfall for me was it makes you feel Like Crap! Everyday for me, makes it tough to use for me.... I have a hard time taking something that i KNOW is going to make me feel like shit. No pain no gain though I guess