The smoke from second-hand cannabis can trigger positive drug tests

According to a recently published study, exposure to second-hand cannabis smoke may result in detectable cannabinoids being detected in the hair. This complicates forensic hair analyses.

The hair follicle test can detect marijuana use for a long period of time, usually up to 90-days, depending on how much hair is tested. These tests are sometimes conducted for medical, legal or employment purposes. The hair follicle test isn’t 100 percent accurate. It can’t determine an exact date due to the fact that hair growth rates are different.

Researchers from Italy’s University of Bologna set out to assess whether detectable hair levels of delta-9 tetrahydrocannabinol (Δ9-THC) and cannabidiol CBD could occur from short, single and repeated passive exposure to cannabis and “light cannabis” (low in THC, high in CBD) smoke – and whether the two products could be distinguished.

Several volunteers were subjected to weekly 15-minute exposures to low-Δ9-THC (0.5 %) cannabis smoke over a month that was delivered by a pump inside a car. After a 1 month washout period (when participants weren’t exposed), exposures were repeated under the same conditions with high-Δ9-THC (5 %). Following each exposure, samples of hair and urine were taken.

While the urine tests always proved negative, hair samples were positive for CBD after exposure to “light cannabis”, and for THC after exposure to high-Δ9-THC cannabis, with levels also typical of drug use.

Researchers conclude:

Our study demonstrated that even short exposures to “light” cannabis or cannabis could cause hair contamination in vivo, underscoring the importance of a cautious interpretation of hair analyses in forensic toxicology.

The term “in vivo”, which means in the live body of an animal or plant, is used.

This study was conducted to find out more about the effects of smoking on health. has been published The journal Forensic science International. In vitro means in an artificial environment. study from last year by some of the same researchers that concluded hair analysis might allow testing to determine whether external contamination by products containing low or high Δ9-THC, but not the delivering mode.

The National Organization for the Reform of Marijuana Laws in the USA (NORML), which is a part of the National Organization for the Reform of Marijuana Laws, has released a statement on the most recent research. said:

“NORML criticizes drug testing in the workplace, including blood tests, urine tests, oral fluid tests and hair tests. These tests are not accurate in determining behavioral impairment and recent drug consumption.”