A new study published in the Journal of Analytical Toxicology has challenged the validity of using THC blood levels as a measure of impairment for cannabis users. The study, conducted by researchers from the University of British Columbia and the University of Toronto, found that THC blood levels did not correlate with impairment or the time of last cannabis use.
The Problem With THC Blood Tests
THC, or tetrahydrocannabinol, is the main psychoactive compound in cannabis that produces the high sensation. However, unlike alcohol, THC does not have a clear relationship between its concentration in the blood and its effects on the brain and behavior. This makes it difficult to determine if a cannabis user is impaired or not based on a blood test.
One of the reasons for this discrepancy is that THC is fat-soluble and can remain in the body for a long time after consumption, especially for frequent users. This means that a person can have high levels of THC in their blood even if they are not intoxicated, or low levels of THC in their blood even if they are impaired.
Another reason is that different people can have different levels of tolerance and sensitivity to THC, depending on factors such as genetics, metabolism, and history of use. This means that a person can have low levels of THC in their blood and still be impaired, or high levels of THC in their blood and still be functional.
The Study Design and Results
The study involved 80 participants who were either occasional or frequent cannabis users. They were asked to consume cannabis either by smoking, vaping, or eating edibles, and then complete a series of cognitive and psychomotor tests to assess their impairment. They also provided blood and breath samples to measure their THC levels.
The researchers found that there was no consistent relationship between THC blood levels and impairment across the participants. Some participants had high levels of THC in their blood and showed no impairment, while others had low levels of THC in their blood and showed significant impairment. The same was true for THC breath levels.
The researchers also found that THC blood levels did not indicate the time of last cannabis use. Some participants had high levels of THC in their blood even though they had not used cannabis for several days, while others had low levels of THC in their blood even though they had used cannabis recently.
The Implications and Limitations
The study suggests that THC blood tests are not a reliable way to determine if a cannabis user is impaired or not, and that other methods, such as behavioral and performance tests, are needed. This has important implications for law enforcement, workplace safety, and public health, as many jurisdictions use THC blood tests as a legal standard for impairment.
However, the study also has some limitations, such as the small sample size, the lack of a placebo group, and the variability in the cannabis products and doses used by the participants. The researchers acknowledge that more research is needed to confirm their findings and to explore other factors that may influence impairment, such as the type and potency of cannabis, the mode of consumption, and the individual characteristics of the user.