An investigation in Pennsylvania showed some officers have been trained to look for the tinged tongues

Police officers south of the border are pressing DUI charges on people who have green tongues, suspecting cannabis use, despite any scientific evidence to support them.

An investigation from the York Daily Record in Pennsylvania showed some officers have been trained to look for the tinged tongues.

The paper probed about 1,300 DUI (driving under the influence) cases and found that at least 28 cited observations such as “green coating”, “green film” and “green tint.”

Scott Harper, a defence attorney in West York who recently argued a DUI case citing the tongue theory, calls it “junk science.”

“I don’t even think it’s real,” Harper told the York Daily Record. “They can take pictures of these things. I’m still waiting to see a green tongue someday.”

The National Organization for the Reform of Marijuana Laws (NORML) also weighed in. “The science behind marijuana consumption turning your tongue green is about as sound as the science behind the earth being flat or that lying makes your nose grow,” Erik Altieri, executive director of NORML, wrote in an email to the newspaper.

Nick Morrow, an expert witness on the theory, said he first saw the idea of green tongues indicating impairment and cannabis use in a handbook called, Identifying the Marihuana User.

Detectives who believe in the tongue test back up their methods by citing two peer-reviewed articles — neither of which confirm cannabis changes the colour of someone’s tongue to green.

The Journal of the American Optometric Association published the first article in 1998 and two of the paper’s authors were police officers. The article states that cannabis users “might have a greenish coating” on the back of their tongues if they recently tried the drug, but failed to provide a citation.

Karl Citek, an author of the study who is now an optometry professor at Pacific University in Forest Grove in Oregon, said their report was based on drug enforcement training for police at the time.

The article attempted to rationalize the statement by noting that optometrists could be consultants to police or expert witnesses in testimony if they knew of the program.

Citek told the York Daily Record they did not pursue any experimenting or research to see if cannabis caused a change in the tongue’s colour — but he said he saw it before.

“It was intended to be more educational than anything else,” Citek said. “And, hence, it’s a review paper.”

The Journal of Forensic Sciences contains the second study, published in 2017. Researchers tested blood samples from people who were suspected of driving under the influence and noted that 185 of those drivers had a “coating on the tongue”, but did not specify if that coating was green.

And the first page of report states a conflict of interest. “Authors all work for The Orange County Crime Laboratory testifying on driving under the influence cases, specifically in regard to marijuana, which represents a possible conflict of interest.”

Ariana Adeva, a toxicology supervisor and one of the authors, told the York Daily Record the team never decided if cannabis caused the coating on the tongue, but rather looked at anecdotal accounts from officers and looked for correlations to THC in the bloodstream.

“I think it is a common finding,” Adeva said when discussing the coating. “We did see a good number of cases including it.”

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