Back to top
Drug testing in the workplace is an increasingly common practice and includes: pre-employment drug testing, random drug testing, testing on suspicion, and testing if there is an accident or incident.
However, drug testing does not improve workplace safety, it is ineffective at managing impairment and is highly invasive.
In New Zealand employees can only be randomly drug tested in safety sensitive environments. There is less clarity around other drug testing but it needs to be in-line with any employment agreement and should be consistent with the organisation alcohol and other drug policy.
All drug tests should only be conducted by people qualified to collect the sample and must be analysed by a laboratory to be valid.
While random drug testing has been found to reduce employee drug use, it has not been found to reduce near-misses, accidents or deaths in workplaces.
This is because drug testing detects previous use of drugs, not whether someone is currently impaired or affected by drug use. A lot of drugs only have a short effect if someone uses at the start of their weekend it is unlikely to be still affecting them when they return to work.
While employees may use drugs less if they are subject to workplace testing it is often drug use that was not affecting their work. Requiring an employee to provide a urine sample while supervised is highly invasive of their privacy and does not build trust or respect.
There are major technical limitations to drug testing. A standard drug test can only detect use of five drug categories: cannabinoids (cannabis), amphetamines (methamphetamine), cocaine, opiates (heroin), PCP. This is through detecting metabolites in someone’s urine, blood, hair or saliva. Metabolites are formed as the body breaks down the drug, however the speed of this process varies widely from person to person.
Depending on the sample and the drug, there is significant variation in how long after use a drug can be detected. Some tests are more comprehensive (and expensive) but still only detect a limited range of substances.
The main methods of testing have different limitations:
A positive test result is influenced by many factors including how much and how often the drug was used, and the employees weight, age and how their body processed the drug. The below table gives an indication of detection periods but should not be relied on.
|Cannabis||Up to 4 weeks||Up to 2 weeks||Up to 90 days||12-24 hours|
|Methamphetamine||3-5 days||1-3 days||Up to 90 days||Unknown|
|Cocaine||2-4 days||Unknown||Up to 90 days||1 day|
|Heroin/codeine/morphine||4-5 days||Unknown||Up to 90 days||12-36 hours|
In safety critical work sites where random drug testing has legal grounds to be implemented it is still not an effective mechanism for managing impairment.
Impairment reduces someone’s ability to make decisions or do their job and can be from: tiredness, stress, dealing with grief or a breakup, medications or alcohol and drug use. While breathalysers can measure whether the alcohol someone has drunk is making them impaired, drug tests cannot do this. Knowing if someone used drugs does not mean they were affected by them at work.
Reducing impairment, rather than previous drug use, in the workplace should be the focus. This can only be done through quality management, a culture of reporting health and safety risks, and a system that encourages people to speak up if they notice an issue or someone else who is impaired.