I work in Toxicology, meaning I perform random drug immunoassays, these days it's mostly mining/construction and child protection. I've been called a maggot for what I do. I don't agree with stuff like Marijuana being placed in the same class as Meth, but I don't think people working on mine sites should be doing anything that could affect their work, including drinking alcohol. Even if it were all legal I doubt I'd be out of a job.
That's basically it, yes. If a parent becomes abusive or develops a serious drug habit that they need to go on rehab, they need to stay clean for a certain period of time. Prescriptions are exempt of course. They're observed while doing the test, our company follows a very strict set of guidelines for collection for legal reasons (AS4308), there's a massive market out there for ways to cheat drug tests.