Secondhand cannabis smoke rarely caused positive urine tests at standard cutoffs, but did at lower thresholds | Research

The takeaway

Non-smokers exposed to secondhand cannabis smoke in a sealed room rarely tested positive at the standard 50 ng/mL urine cutoff, but multiple positives occurred at the lower 20 ng/mL threshold.

Read this if you're worried about failing a drug test from being around people smoking cannabis.

Only 1 positive at standard 50 ng/mL cutoff under extreme exposure

What the researchers found

Six non-smokers were exposed to secondhand cannabis smoke in a sealed chamber with six smokers for one hour across three sessions. Urine specimens collected over 34 hours were tested at four immunoassay cutoff levels and confirmed by GC-MS.

At the standard federal workplace cutoff of 50 ng/mL, only a single positive occurred. No positives occurred at 75 or 100 ng/mL. However, multiple positives occurred at the lower 20 ng/mL cutoff, which some testing programs use. GC-MS confirmation showed maximum THCCOOH concentrations in non-smokers ranging from 1.3 to 57.5 ng/mL.

Higher cannabis potency increased exposure levels, but room ventilation substantially reduced them. The authors concluded that positive tests from secondhand exposure are likely rare, limited to hours immediately after exposure, and occur only when exposure is obvious to the person involved.

Why it matters

The question of whether secondhand cannabis exposure can cause a failed drug test is important for workplace fairness. This study shows it is technically possible under extreme conditions at lower cutoffs, but practically unlikely at standard testing thresholds.

The numbers in context

6 non-smokers, 6 smokers. Three sessions. At 100 ng/mL cutoff: 0 positives. At 75 ng/mL: 0 positives. At 50 ng/mL: 1 positive. At 20 ng/mL: multiple positives. THCCOOH by GC-MS: 1.3-57.5 ng/mL range in non-smokers. Ventilation substantially reduced levels.

How the study worked

Controlled exposure study with 6 non-smokers and 6 smokers in a sealed chamber. Three sessions: 5.3% THC (no ventilation), 11.3% THC (no ventilation), 11.3% THC (with ventilation). Urine collected 0-34 hours post-exposure, analyzed by four immunoassays (cutoffs: 20, 50, 75, 100 ng/mL) and GC-MS (LOQ 0.75 ng/mL).

What this study cannot tell us

Extreme exposure conditions (sealed chamber, 1 hour) do not reflect typical scenarios. Small sample size. Only two potency levels tested. Results may differ with different cannabis consumption methods (vaping, edibles produce no smoke).

How to read the evidence

Controlled exposure study with validated testing at multiple cutoff levels. Extreme conditions limit real-world applicability.

When this study was published

Published in 2015 when cannabis potency was lower than current levels.

The bigger picture

Drug testing policies need to balance detection sensitivity with fairness. This study suggests the 50 ng/mL federal cutoff provides reasonable protection against false positives from passive exposure, while lower cutoffs could be problematic for people in enclosed environments with cannabis smokers.

Questions still open

Should drug testing programs consider exposure environment when interpreting near-threshold results? Would multiple shorter exposures accumulate similarly? How do results change with the increasing potency of modern cannabis?

Common questions

Can you fail a drug test from secondhand cannabis smoke?

Under extreme conditions (sealed room, 1 hour, no ventilation), it is technically possible at lower testing cutoffs. At the standard federal workplace cutoff of 50 ng/mL, only one positive occurred. In normal settings, it is very unlikely.

Does ventilation help prevent secondhand exposure?

Yes. In this study, ventilation substantially reduced the levels of THC metabolites in non-smokers' urine, demonstrating that adequate air circulation is an effective protection against secondhand cannabis exposure.

Read the original research

Non-smoker exposure to secondhand cannabis smoke. I. Urine screening and confirmation results.

Journal of analytical toxicology, 39(1), 1-12

View on PubMed ↗Publisher’s paper ↗

Citation

Cone, Edward J; Bigelow, George E; Herrmann, Evan S; Mitchell, John M; LoDico, Charles; Flegel, Ronald; Vandrey, Ryan. (2015). Non-smoker exposure to secondhand cannabis smoke. I. Urine screening and confirmation results.. Journal of analytical toxicology, 39(1), 1-12. https://doi.org/10.1093/jat/bku116