3-4 weeks? Were the hell u guys getting your stats from? I smoked 8 days before a piss test for a job, before that, i was smoking once every other day... i went to the head shop, and bought what is called "The Stuff"...drank it, and pissed clean..
Then I had to do another piss test, about a month after. I had smoked Six days before(it was a random piss test, no time to prepare or anything), before that, i was smoking twice a week, I tested clean. SIX DAYS AFTER SMOKING!!!
Mary jane takes only 3-4 days to get out of your urine...but it also depends on how often you smoke. If your bro has been smoking three times a day for the past two weeks, he is fucked. If not, he should be A-OK
