The human being is fascinating when you think about how people act and react to the world around them: instinctively, naturally or adversely - and it's all done while processing information that comes via our senses.
This information of course is directed and processed through the brain, and that then goes onto controland process other parts of the body to make the next move or action.
Now as much as most people think the human body is amazing, (and it bloody well is,) there is only so much abuse and punishment it can take AND NOT EVERYONE IS THE SAME.
Impairment of the brain and body can last longer and stronger in some people than others.
1: Alcohol, which is a drug has much written literature written produced that can verify this and other drugs eg: Cannabis, Cocaine, Meth', etc have also similar literature produced.
2: People have different metabolisms, different degrees of resistance/immune levels, health issues, mental issues, etc, etc, not one size fits all as a description of a person.
3: Different drugs have different degrees of effect on each person.
4: This is a link to a USA Recovery clinic blog which backs up what has just been written:
Being under the influence or impairment of drugs or alcohol doesn't always show as obvious as some people think, especially if character change is only slight and progressive over time. As much as people think they know a character they can become accidentally complacent over time of the character.
This is why ZERO TOLERANCE is generally written into Employment Agreements, Health and Safety agreements and policies regarding Drugs and Alcohol.
It is generally also written that persons employed are to turn up to their place of employment in a fit and stable state to carry out their duties described in their employment without compromising their employer, other employees, contractors or property – something like that with variables I'm sure. But you get the gist'.
If there is any doubt or you "think you know" but "don't really know" then DO SOMETHING about it. The consequences are just too high.
1: Make sure policies and procedures are in place first and foremost regarding employment agreements and health and safety.
2: I'd encourage open discussions within your work place with your entire team.
3: Be open and honest about the discussion subject/s Drugs and Alcohol, not just the effects but also about the possibilities around betterment going forward for the company and the employees.
I'm more than happy to discuss policies, procedures, and testing methods. Testing is not as invasive as what people think. Top sports people/athletes do it all the time now to prove they are clean and who doesn't want to a clean member on their team.
Both the Business, Managers and Employees can act for betterment going forward with knowledge of what is, than not really knowing at all and a "she'll be right" attitude.
It's better to know than not to know.