Evidence shows that while random drug testing can reduce employee drug use, it does not reduce near-misses, accidents or deaths in the workplace.
This is because drug testing detects previous use of drugs, not whether someone is currently impaired or affected by drug use. Many drugs only have a short effect, so if someone uses at the start of their weekend it is unlikely to be 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. Additionally, requiring an employee to provide a urine sample while supervised is invasive of their privacy and can negatively impact employee trust.
There are significant scientific limitations to drug testing. A standard drug test can only detect use of five drug categories: natural cannabinoids (cannabis), amphetamines (methamphetamine), cocaine, opiates (heroin), PCP. This is achieved by detecting known metabolites in 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.
The duration after use that a drug remains detectable varies widely depending on the person, type of sample and the drug. Some tests are more comprehensive (and expensive) but still only detect a limited range of substances.
The main methods of testing have different limitations:
- Urine: most common sample type, least expensive, highly invasive
- Blood: uncommon in a workplace, less expensive, invasive
- Hair: uncommon, very expensive, less invasive
- Saliva: least invasive but also least reliable testing method that often requires a follow up test
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.
| Source: erowid.org | ||||
| Substances detectable | Urine | Blood | Hair | Saliva |
| 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 may still be of limited effectiveness at 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, other drug tests cannot do this. Knowing if someone used drugs does not mean they were affected by them at work.
Reducing impairment in the workplace, rather than any drug use, 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.
