Detection vs Impairment in Workplace Drug and Alcohol Testing: What Employers Must Understand

One of the most common misunderstandings in workplace drug and alcohol testing is the assumption that detection automatically means impairment.

In reality, these are two very different things. Confusing them can lead to unsafe decisions, unfair treatment of employees, and significant risk for employers.

Understanding the difference is essential for any organisation operating a workplace drug and alcohol testing programme.

What Is Detection?

Detection simply means that a substance has been identified in a person’s system through a drug or alcohol test.

Drug tests detect the presence of substances or their metabolites. Depending on the substance, this detection window may extend long beyond the period where any effects are present. In other words, a person may test positive without being impaired at the time of testing.

This is particularly important in modern workplaces where prescribed medications and legally prescribed substances can also be detected.

What Is Impairment?

Impairment relates to a person’s ability to perform their role safely and effectively at that moment in time.

Impairment is behavioural and functional. It may present through reduced coordination, slowed reaction times, poor decision-making, confusion, or visible changes in behaviour or performance.

Unlike detection, impairment is about safety risk in real time.

The Problems Caused by Getting This Wrong

When employers treat detection as proof of impairment, several issues arise:

• Employees may be treated unfairly despite being fit for work.

• Managers lose confidence in the testing process.

• Workplace trust reduces.

• Legal and HR risks increase due to inconsistent decision-making.

• Safety risks remain if impairment is not properly recognised.

Equally, assuming someone is safe simply because a test is negative can also create risk if behavioural signs of impairment are ignored.

Testing should support decision-making, not replace it.

How to Recognise Possible Impairment

Managers should never be expected to diagnose substance misuse. Instead, they should look for observable indicators such as:

• Unsteady movement or poor coordination

• Slurred or slowed speech

• Strong smell of alcohol

• Confusion or difficulty concentrating

• Sudden behavioural changes

• Unusual risk-taking or poor judgement

• Noticeable decline in performance or awareness

These indicators should always be considered in context and documented objectively.

What To Do If You Believe Someone Is Impaired

If an employee appears impaired to the point that safety may be affected:

1. Remove the individual from safety-critical duties immediately.

2. Have a calm, private conversation focused on safety, not accusation.

3. Record observable behaviours, not assumptions.

4. Follow workplace policy for reasonable cause or for-cause testing.

5. Ensure the individual can leave safely if required.

6. Manage the situation consistently in line with company procedures.

The focus should always remain on safety and fairness.

The Reality

Drug and alcohol testing is most effective when employers understand what tests can and cannot tell them.

Detection provides information. Impairment determines risk.

Workplaces that understand this difference create safer environments, make better decisions, and avoid unnecessary conflict.