Cannabis Study Highlights Deficiencies Of Hair Follicle Tests
Drug testing is very common across the globe, and for better or worse, it is big business. A recent market analysis found that the global drug testing industry is worth $14.67 billion in 2025, and is projected to grow to $23.05 billion in market value by 2034.
While the estimated current value and future growth of the analysis are for testing for all substances, and cannabis testing is just a subsector of the wider industry, it generally highlights how much money is involved in the world of cannabis testing.
The motivation behind testing for cannabis use is questionable at best, in my opinion. Obviously, no responsible person wants people to be impaired while operating a motor vehicle on a public roadway or to be impaired while operating dangerous equipment while working. However, testing for cannabis impairment is not an exact science, as evidenced by the results of a recent scientific investigation conducted in Italy.
A team of researchers affiliated with various health and academic institutions in Italy examined the results of hair follicle tests that focused on detecting the presence of the cannabinoid tetrahydrocannabinol (THC). The findings from the examination were published in the journal Forensic Science International.
“The aim of the present study was to assess whether detectable hair levels of Δ9-THC and CBD could arise in vivo from short, single and repeated passive exposure to cannabis and “light cannabis” and whether the two products could be distinguished.” the researchers stated about the focus of their study.
“Four volunteers underwent weekly 15-minute exposures to low-Δ9-THC (0.5 %) cannabis smoke, delivered by a pump inside a car, over a month. After 1 month of washout, exposures were repeated with the same scheme with high-Δ9-THC (5 %). Hair and urines samples were collected after each exposure. Hair samples were tested, with and without a washing step (total n = 72), by liquid chromatography tandem mass spectrometry for Δ9-THC and CBD. Urines were tested for drug metabolites (LOD: 1.66 ng/ml).” the researchers stated about their methodology.
“No accumulation of drugs over exposures was shown. Urines always tested negative. Washed hair samples were positive for CBD (mean 0.05 ng/mg) after exposure to low-Δ9-THC cannabis, and for Δ9-THC (mean 0.02 ng/mg) after exposure to high-Δ9-THC cannabis, with levels also typical of drug use.” the researchers found.
“Our study showed that hair contamination could arise in vivo even after short single exposures to cannabis and “light cannabis”, underlining the need for a careful interpretation of results of hair analysis in forensic toxicology.” the researchers concluded.
In laypeople’s terms, the results of the study found that simply being around cannabis smoke was enough for a hair follicle test to determine that a person had THC in their system, and thus ‘was a cannabis consumer,’ even though that may not actually be the case. It highlights one of the many deficiencies of hair follicle testing when it comes to cannabis, and why the widespread use of hair follicle testing for determining cannabis use is ridiculous.
