Define "drugs".
Alcohol is a drug, as is nicotine. Both are accepted by society but a drug nonetheless.
I'd like to think that, as a professional, you're responsible enough to have common sense.
I wouldn't want someone who's under the influence to take care of children but a glass of beer or a joint consumed the evening before would not be an issue for me.
Probably an European thing.
I think they mostly test for methamphedamines, cocaine, THC and opiate metabolites.