How does a pre-employment drug test work?

[Twon]

Say a company did pre-employment drug testing. When would they typically do that, and would they give you a warning or a few days notice before doing it? Just wondering if they'd do it at an interview, or if its something more like, they test you once you are given the job or something?

[ReNeE]

when you interview they will give you a place and phone # to be tested. you call them and make an appt. the employer will probably give you a week to go get it done. thats how it worked for my husband anyway