It depends quite a bit on the individual person, how often you've smoked, how much you smoked, and what type of drug test is used. Overall, detectable traces of marijuana can stay in your system anywhere from 2 weeks to 2 months after the last time you've smoked. It tends to lean towards the longer range if you're subjected to second hand smoke, etc. And certain types of tests, such as a test of a hair sample, can detect it up to 6-8 months after your last use.