As an employer, you have a duty of care to all your employees when they are carrying out their roles. Much of this is a legal obligation, however, many employers believe they also have a moral obligation too, and this is why many of them will allow employees paid leave for mental health counselling or for drug rehab programs, for example.
One of the problems that employers face, is that in most cases they are not qualified to identify the symptoms of someone who is going through a personal crisis. The other issue is that if someone wishes to keep a problem they are having to themselves, they have the right to do so, as long as it not affecting their work.
In the case of someone who has a problem with drugs, the situation is different as, even if an employer has no formal training on the matter, there are some obvious tell-tale signs that someone is using drugs. Even if that person tries to keep their drug use a secret, their actions, and behaviours can give away the fact that they are. Here are some to look out for if you suspect someone is taking drugs.
Actions Out Of Character
If you have known an employee for some time, and they start to act in a manner that is completely out of character, then drug use could be the cause. Examples include a usually lively person becoming introverted, or conversely, someone who tends to be quiet and shy becoming very outgoing and in extreme cases, outwardly aggressive in some situations.