not exactly true
"all DoD personnel undergo random drug testing. Most people get popped for a test twice a year or so. Failure = dishonorable discharge, do not pass go, do not collect $200."
It depends on quite a few things. For example what drug shows up in your urinalysis, if you gave a statement (confession) before the results were back indicating you had drugs in your system, the current drug policy atmosphere where you are stationed, and yes unfortunately it depends on who you are.
I have seen many people simply get sent to a rehab program when they "piss hot" showing cocaine or marijuana in their system. A few had been doing extacy and got pulled for a urinalysis and subsequently dishonorably discharged.
It's not as easy to get kicked out as it may have been in the past. I myself had somewhat of an experience with this. It's regarding how I found this website to begin with. ;)
http://www.theregister.co.uk/2001/05/08/us_airman_charged_in_korean/
http://ww2.pstripes.osd.mil/01/jul01/ed072701g.html <-- by this time i had been relieved of some rank heh
I continued to serve my country until 2003 and received an Honorable discharge.