It is a common misconception that all drug and alcohol tests have a goal to identify impairment in an individual. While that is what drug and alcohol tests do by their simplest definition, they are part of a much broader identification process. Drug and alcohol tests can prove impairment, however they are meant to identify RECENT USE, which then helps identify safety risks within a workplace and among employees. It is also crucial to keep in mind that impairment can arise from factors other than drugs and alcohol, like fatigue, family crisis, exposure to extreme weather, etc.
The degree to which different substances impair different people can vary greatly, and is not an exact science. Take THC for example:
“Impaired behavior from acute use differs between occasional users and long-term users. There is good evidence that chronic frequent cannabis users exhibit less impairment from acute THC than do occasional users, but the degree to which impairment is mitigated in safety-sensitive activities is unclear.” 
Therefore it would be difficult to identify and label someone as impaired from a positive drug test.. So when these tests come back positive, it proves recent use which left high enough concentration levels of the substance in a person’s system to identify that their substance use is frequent enough to cause concern for safety.
So while there is no doubt that someone impaired on the job poses a safety risk, drug and alcohol tests are designed to identify when employees are using enough of a substance outside of the job to still pose risks to their own safety, and that of others.
If you and your organization need assistance in assessing the need for testing, or the safety risks that could be dangerously impacted by impairment, then contact CannAmm and we will assist you in creating suitable policy and in delivering the drug or alcohol tests, should the need arise.
Both impairment and recent drug or alcohol use are cause for concern. But remember, impairment may not always stem from drug and alcohol use.