text: how long does marijuana stay in your system? my best friend is taking a drug test next week, and she is scared becasue she has been smoking. um she said the last time she has smoked was may 26. uuh.....what should she do?? she could be out of luck depending on what test they use.  a urine test can detect the presence of thc up to a week afterward, but there are several tests which check other tissues, and it has become very popular as of late to require a hair test because evidence of drug use stays in hair for a year.  she should stop smoking pot if she wants to pass a drug test.  they've gotten awfully good at catching you, otherwise.