That’s two of the reasons why drug testing is bullshit:

A) Alcohol isn’t considered a part of it and you can fail a drug test if you had weed a week ago but pass if you got drunk before pissing in the cup.

and

B) If you can do your job efficiently, who cares what substances you take? If someone shows up to work drunk or high and can’t do their job, by all means, fire them. But so many people do their work just fine drunk or high.