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THC Levels in Breath and Blood Tests not Correlated to Impairment

thc breath blood tests impairment

A recent study has found that THC levels in breath and blood tests do not correlate with impairment – a find that confirms previous studies on the same subject. Although there are now multiple findings confirming that blood and breath samples cannot be used to judge impairment, many states continue to uphold per se limitations on cannabis – following the trend of lawmakers enforcing outdated and unfounded principles in their policies. Let’s hope they catch up to the science of cannabis soon.

THC And Impairment In The US

In the United States, numerous states have implemented per se limits to establish cannabis impairment, often 5 ng/ml of THC, and it is illegal to drive a vehicle with blood THC concentrations exceeding the per se level. It is a fact that THC can persist in a user for long periods of time – post-consumption – and so per se limitations are often criticized for their ability to implicate drivers who display above the legal level of THC in their blood or breath but are not actually impaired.

Studies have shown that there is another factor to consider which makes these per se limitations unfounded, such as one published by Scientific Reports, which found that THC identified in blood tests or breath does not suggest impairment.

Regardless of these findings – which simply confirm many other studies that provide similar outcomes – numerous states still implement policies regarding THC and impairment that do not align with the facts.

About The Study 

THC levels in the blood and breath of regular cannabis consumers were measured before and after they smoked. These levels and the duration of the participants’ impairment after inhalation were measured by the researchers.

At baseline, the majority of patients had residual THC levels in their blood (at levels of 5 ng/ml or above), meaning that despite “the absence of any impairment,” THC was detected in these patients’ blood. This shows that the evidence of THC in blood or breath is not an accurate method for distinguishing cannabis impairment.

The scientists discovered an inverse link between THC blood levels and performance disablement after subjects inhaled cannabis.

They stated that their findings show that single measurements of specific delta-9-THC blood concentrations do not correlate with impairment and that using per se legal limitations for delta-9-THC cannot be justified scientifically as of now – we’d appreciate it if state lawmakers would get on board the scientific-fact-train.

The authors of the study also discovered the presence of THC in the patients’ breath at baseline, despite the absence of any indicators of impairment. “Our findings are consistent with those of others who have shown that delta-9-THC can be identified in breath up to several days after last usage,” they concluded. Because the dominant methods for breath-based testing for recent cannabis use rely only on the detection of delta-9-THC, false-positive test results could occur if delta-9-THC is detected in breath outside of the impairment window.”

Final Thoughts

Around a dozen states in the United States have adopted per se or zero-tolerance per se requirements in their traffic safety legislation.

Many cannabis advocates have long opposed the use of THC blood thresholds as predictors of impairment, and in particular per se driving safety limitations, because they are not reliably connected with changes in individuals’ performance. Alternatively, performance-based tests, like DRUID, are being advocated for.

The researchers came to the conclusion that they couldn’t find any further evidence that single measures of delta-9-THC in the blood can’t prove impairment, and that single measurements of delta-9-THC in exhaled breath can’t prove impairment either. It’s time that the law catches up with the science of the matter.

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