3 years is not true... rule of thumb is three smoking sessions in 90 days and you should be clean enough to pass one. But this all depends on your smoking amounts during each session. Most pre-employment drug screens are either saliva or urine. If they do a hair test we can help you to pass but it's a shitty process. You will have to bleach and redye your hair twice as well as purchase a zydot shampoo.