Not a problem for us. Are you sure? You probably forbid the use of alcohol and drugs while people are at work. If you are in a high risk sector, you may back this up with random blood tests. If this is something important for you, you must have it written into employment contracts, otherwise your staff can refuse.
Much more likely to be an issue is people at work but affected by the night before. Or taking time off because their “food poisoning” is actually a hangover. Alcohol in particular can get to be a destructive habit which means that a worker is constantly less than their best. If someone is at work but still has alcohol in their blood, they could be sufficiently affected that driving or the use of machines is problematic.
This sort of situation is difficult to deal with. The best approach is to encourage openness about alcohol and drug use, and to be supportive. A disciplinary route may be required, but always with the carrot as well as the stick. The person may desperately want to stop, for lots of reasons, but find it hard. You can help.
In particular, think about the workplace culture. Are staff drinks on a Friday evening running to excess? Making people feel excluded if they don’t want to drink? Does the company put on parties with alcohol provided, and are good non alcoholic options available?
Another important issue is prescription medications. Many medications can affect someone’s performance at work, and in particular their fitness to undertake high risk tasks. This may improve once the person has adjusted to the medication, but how can you manage a problem you don’t know about? It is important that all your staff are aware of the need to report any new medication they take which has a warning on the label. You must accept, though, that they may be reluctant to tell you. An open culture, where staff know that they will be supported and not punished for their ill health, gives you the best chance of knowing about the risk so that you can manage it.
It is always worth covering alcohol and drugs in your policies and employment documents. Make sure workers know that they will be supported if you become aware of a problem. Having the company approach documented also helps you to take appropriate action when needed. It is one more possible risk which needs to be assessed ahead of any problems.