I believe it depends on company policy. Some places just won't call you back, others will call you and tell you you didn't get the job, but won't say anything about the test.

You should really try to not take any drugs for a month prior to a pre-employment test, but if you have to, there are ways to get past them. I really recommend just stopping beforehand though, as neither a detox drink or a piss filled condom is particularly glamorous or fun.