Kronic is right. An individual is expected to be clean, therefore dont expect the employer to inform you that "youve tested negative". In the world of drug testing, no news means good news. If there were any issues with the drug test, you will be notified one way or another.

As Kronic advised, contact the employer and ask a question or two for the purpose of "getting the ball rolling", so to speak. One good example is to ask for your "start date". The employers response oughta clue you in as to whether youre good to go, or if the employer had simply moved on to the next candidate for hire.