So, we call this approximate calculation as half life. If you have smoked marijuana then the drug will stay for 3 to 30 days. This is normal for the common drugs. But in the case of marijuana, this can be detected even after a month in Urine drug test marijuana. Marijuana will stay in your system for 10 days if you have been smoking occasionally. If it is smoked on regular basis it will be there up to 45 days and if you smoke constant pace then it will be in the system for as long as 90 days. http://clnk.me/1yc0I.