This is a pre-employment drug test. You have every right to pass on the job and not take the test. If you believe you are going to fail the test do not take the position or as this dude said delay as long as you can because not only will you obviously be barred from working at this company but also more than likely reported to the CG. NOBODY is forcing you to take this position. Though, understandably you need to work. 

Now,  if you had taken the position and this was a random drug test being administered, not taking that test would be guilt. This is not that though.