By Expert Warning On Outdated Testing
Dr Georges Petitjean has warned that workplace drug testing has failed to keep pace with cannabis reform. Writing in Personnel Today, he said a laboratory can answer the wrong question perfectly.
An employee may provide a sample that tests positive for cannabis. The analysis can be technically sound and the chain of custody secure, yet the result may still not show impairment.
Petitjean raised the warning during September, which is Recovery Month. He argued that approaches to employee substance use have barely evolved.
His article explores how businesses can keep pace with changing medicine, legislation and the modern workforce. He says employers now face a practical difficulty in interpreting cannabis results.
The warning comes as medical cannabis use grows in the UK.
Legal Prescriptions Complicate Results
The legal landscape shifted in 2018, when certain cannabis-based products for medicinal use were moved into Schedule 2 of the Misuse of Drugs Regulations. This created a lawful route to prescription.
Recreational cannabis did not become legal. Yet cannabis can now sit on both sides of a workplace drug policy, as prescribed medicine and illicit drug.
The Care Quality Commission reported a 130% rise in private prescription items for unlicensed cannabis-based medicinal products between 2022-23 and 2023-24. Those are prescription items, not patients.
A prescription does not make interpretation simple. An employee may be using cannabis as prescribed, may also be using illicit cannabis, or both.
A routine positive result does not establish the source of every detected cannabinoid. Nor does it establish current impairment.
Impremment Remains Hard To Measure
Urine can remain positive long after acute effects have passed. Oral fluid is generally more closely related to recent use.
Neither result, by itself, establishes that somebody is impaired at work. Presence and impairment are different things.
THC, the main compound responsible for the high, can impair attention, tracking and other abilities relevant to driving and safety. But there is no simple biological number that converts a THC concentration into a verdict of fit or impaired.
Research has found blood and oral-fluid THC concentrations to be relatively poor indicators of cannabis-induced impairment. Petitjean says this leaves employers with a practical difficulty.
He suggests greater emphasis on observable performance, conduct and occupational-health assessment in non-safety-critical roles. In safety-critical roles, he warns, the consequences of getting the judgment wrong can be catastrophic.
