An Increase in Pre-Employment Cannabis Positivity Is Not an Increase in Measured Impairment
A clinic’s rising cannabis urine positivity rate measures a change in detected exposure, not a measured rise in workplace impairment. A California retrospective study also demonstrates why absolute and relative changes must be reported together.
Which result counted as positive?
Sharip and Razavi reviewed 21,546 pre-employment screenings from one occupational medicine clinic during 2017–2022. Initial urine immunoassays used a 50 ng/mL THC-COOH cutoff, with gas chromatography–mass spectrometry confirmation at 15 ng/mL.
The target was a metabolite in urine. Neither stage measured work performance, attention, or a contemporaneous blood THC concentration.
A large relative change from a small baseline
Positivity increased from approximately 0.12% to 0.94%, a statistically significant trend. The large reported relative increase accompanied an absolute change of about 0.82 percentage points. Omitting the starting rate can make the practical scale difficult to assess.
The paper describes the ages and sexes of positive cases, but lacks complete demographic denominators for everyone screened. A larger share of positives in a subgroup does not, without those denominators, establish a higher subgroup positivity rate.
What caused the trend?
The time period followed changes in cannabis availability, but the study did not randomize access or establish legalization as the sole cause. Selection into screening, clinic population changes, exposure patterns, and other unmeasured factors could contribute.
The results are useful for understanding this clinic’s testing experience. They do not estimate the number of impaired workers or determine a particular applicant’s fitness. Any employment-law question requires current legal analysis separate from the paper’s historical testing data; the analytical finding itself concerns metabolite detection.
Related reading: why urine and blood results are not interchangeable.
Primary research
Akbar Sharip; Roshan Razavi. Pre-employment urine drug screening: examining trends in THC-COOH positivity rates post-legalization of recreational cannabis in California – a retrospective review. Journal of Occupational Medicine and Toxicology (London, England) (2025). DOI: 10.1186/s12995-025-00468-3.
