TL:DR - Works great to help pass a drug test if you smoke... not cigarettes... and you follow the directions.Never failed me once! I'm not afraid to admit that I smoke. Recreational reasons, medical reason, any reason really. Anyways, that's not the point.The point is, every time I've had to take a drug test for a job, or anything else that requires a pre-screen drug test, I have drank one of these and followed the directions on the bottle to a T and it has never failed me.I'm not saying you should be smoking the day of or even the day before. But, I have smoked the day before a drug test, drank this and had no issues passing. I usually get a bottle of this or the XXClean as, same stuff just for larger people, and a jug of 100% no sugar added cranberry juice. Drink the cranberry juice the night before and the morning of. Then, roughly an hour to 1.5 hours before I need to leave for my drug test, I drink the ready clean. Wait 15 minutes and fill the bottle back up with water, then drink all of that water. After that, just keep filling the bottle back up and sip on water for the next hour. During this hour you should start to urinate frequently. After an hour to 1.5 hours and a few bathroom breaks later, you're ready to go take your drug test. You have roughly a 6 hour window after drinking the drink, to go take your drug test. I cannot vouch and say that it has worked for me after that many hours. I personally have never waited more than 3 hours before going to drug test but have heard of other people doing it and being ok. The only thing I can say is that your chances of passing, because of the drink, are greatly diminished after 6 hours.