Pre-employment urine drug screening positivity for THC increased from 0.12% to 0.94% between 2017 and 2022 at a California hospital clinic, with the proportion of positive females rising from 25% to 62%.
Occupational medicine physicians, HR professionals, employment law practitioners, and cannabis policy researchers.
What the researchers found
THC-COOH positivity rate increased from 0.12% in 2017 to 0.94% in 2022 (Cochran-Armitage Z=5.19, p<0.001), a 683% relative increase. Among positive cases, 76% were aged 20-39 (mean: 29 years). The female proportion of positive cases rose dramatically from 25% to 62.2%. Median THC-COOH levels ranged from 60 to 176.5 ng/mL.
Why it matters
Pre-employment drug testing policies were designed when cannabis was illegal everywhere. As legalization spreads, the sharp increase in positive tests raises questions about whether cannabis testing should remain part of employment screening, especially since urine tests detect past use rather than impairment.
The numbers in context
21,546 screenings total. 92 THC-positive (0.44% overall). 2017: 0.12% (4/3,215). 2022: 0.94% (45/4,784). 683% relative increase. Female proportion of positives: 25% to 62.2%. Mean age of positives: 29 years. Median THC-COOH: 145.0 ng/mL (IQR: 309.5).
How the study worked
Retrospective analysis of 21,546 de-identified pre-employment urine drug screenings from 2017-2022 at a university-based hospital occupational medicine clinic. Initial immunoassay screening (50 ng/mL cutoff) followed by GC-MS confirmation (15 ng/mL). Cochran-Armitage trend test assessed temporal trends.
What this study cannot tell us
Single clinic at one hospital system. Cannot determine if positive results reflected increased cannabis use or decreased abstinence before testing. Missing demographic data for the total screening population limits subgroup analysis. Low overall positivity rate means small absolute numbers of positive cases.
How to read the evidence
Large screening sample with confirmed results and validated trend analysis, but single-site design and missing demographic data for the overall population limit conclusions.
When this study was published
Published 2025, analyzing 2017-2022 screening data.
The bigger picture
California's Assembly Bill 2188 (2024) restricts employers from using cannabis urine testing in hiring decisions, recognizing that these tests detect past use rather than current impairment. This study provides the empirical backdrop for that legislative shift, showing that positive rates increased substantially after legalization while the overall rate remained under 1%.
Questions still open
- Whether the continued increase in female positivity reflects changing cannabis use patterns or changing workforce demographics
- How employers will adapt testing policies as impairment-focused testing replaces urine screening
Common questions
Does a positive THC test mean someone was impaired at work?
Why did the female positive rate increase so much?
Read the original research
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), 20(1), 29
Citation
Sharip, Akbar; Razavi, Roshan. (2025). 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), 20(1), 29. https://doi.org/10.1186/s12995-025-00468-3
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