i just had to take one friday. it all depends on how much you smoke. if you are like me and smoke every day then four days might be enough to get it out of your system but i wouldnt say for sure. the best simplist easiest way to do it is just go down to your local head shop and get some synthetic urine, its called " number 1" its a belt that you put around your waist, it has a warmer that you put on it that keeps it the ideal temp. between 98*-100*F . i did it and it was so simple. i highly recommend this over stressing drinking hella water and not even knowing if you are clean for sure. again i highly recommend it : D