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More Than 90% Of Smokable Hemp Samples Analyzed By Researchers Contained Illegal Amounts Of THC, New Federal Study Finds



A recently published analysis of smokable hemp products by researchers at the National Institute of Standards and Technology (NIST) found that the vast majority of samples–about 93 percent—contained more than 0.3 percent THC, meaning they in fact qualified as federally illegal marijuana.

Under the 2018 Farm Bill, which legalized hemp nationwide, cannabis products must contain less than 0.3 percent THC in order to be defined as hemp. Those with higher THC levels remain federally prohibited as a Schedule I controlled substance. The distinction is especially important, the report says, in determining whether cannabis seized by law enforcement is legal hemp or forbidden marijuana.

In the new study, researchers at NIST—an arm of the Commerce Department—and the State University of New York (SUNY) Albany analyzed 53 smokable hemp products from five commercial manufacturers for a variety of cannabinoids, including delta-8 THC, delta-9 THC, THC-A and total delta-9 THC. The manufacturers and product names are not included in the report.

“Over 90% of the samples analyzed by NIST were determined to have a total total Δ9-THC mass fraction above 0.3 % even though samples were being marketed as hemp,” says the report, published last month in the journal Forensic Chemistry. “Surprisingly, often the associated online documentation reported total Δ9-THC mass fractions of ≥0.3 %.”

“All samples were sold as smokable hemp with Δ9-THC levels less than or equal to the federal limit of 0.3 %,” the study, which was funded by the Department of Justice’s National Institute of Justice, says. “However, the LC-PDA measurements at NIST indicated that ≈93 % of the samples were above the 0.3 % federal limit. Nearly half of the online documents provided by the manufacturers differed from corresponding product labels.”

Direct comparison of NIST results to online documentation provided by manufacturers of 22 samples found that levels “differed by ≈55 % for total Δ9-THC, ≈68 % for THCA, and ≈18 % for Δ9-THC.”

“Poor agreement,” the study suggests, could be due to differences in testing methods, the “inhomogeneity” of samples themselves leading to varied testing outcomes, batch-to-batch variability, storage conditions “and/or product labels or online documentation that are not representative of actual products.”

Since the 2018 Farm Bill, the report notes, the cultivation and manufacture of hemp has boomed. A 2021 report from the U.S. Department of Agriculture (USDA) estimated hemp production in the country to be valued at $824 million, with roughly 76 percent of all hemp production being “floral hemp,” which includes smokable hemp. Such products are largely unregulated, often available online or in smoke shops or convenience stores and sold regardless of the buyer’s age.

“Now, with a quantitative limit [on delta-9 THC], method accuracy is of paramount importance since legal actions are based on the resulting measurements,” the new study says.

As highlighted in the National Institute of Justice’s post on the new study, NIST researchers used “an established liquid chromatography with photodiode array detection (LC-PDA) method using a methanol extraction procedure” to arrive at the results.

Researchers took between 10 grams and 20 grams of each plant sample and ground it in a “small portable Magic Bullet grinder in four or five separate 5 s pulses to represent similar procedures forensic laboratories have been using to measure total Δ9-THC in seized cannabis plant samples.” The mixture was then extracted using a conventional method “which included a modification of using MeOH (methanol) instead of ethanol in the original method.” After further processing, cannabinoid measurements were taken.

The findings showed notable departures from manufacturer-provided THC levels. “The NIST-determined and manufacturer mass fractions” the report says, “were significantly different for most samples.”

“These studies demonstrate the need for accurate analytical measurements, batch homogeneity measurements, appropriate long-term storage conditions, and updated product information,” wrote the five-author team. “These results also highlight the need for reference materials in the cannabis industry to establish measurement accuracy.”

One indication that storage conditions could play a role is that “NIST values were generally higher for Δ9-THC and lower for THCA,” the study says “indicating decarboxylation of THCA and conversion to Δ9-THC with aging.” The same chemical conversion happens when heating cannabis, such as through smoking.

Federally funded research published earlier this year identified two new methods of distinguishing marijuana and hemp by more precisely determining THC content in cannabis flower and edibles. The aim of the initiatives was to streamline the testing process to help resolve crime lab backlogs that have increased since hemp legalization, complicating cannabis-related cases.

The LC-PDA method used in the latest study was not one of those two procedures. Researchers noted that their process “separates 11 cannabinoids in less than 10 min.”

NIST’s separate gas chromatography-mass spectrometry (GC-MS) method has already led to the creation of new standard operating procedures for labs, and the results have been incorporated into training practices for the Montgomery County Police Department and Maryland State Police.

U.S. Customs and Border Protection (CBP) also put out a solicitation in 2022, seeking portable marijuana analyzers to quickly identify cannabinoid profiles and help distinguish between marijuana and hemp.

The Drug Enforcement Administration (DEA) separately announced in 2019 that it was seeking a device to “provide specificity to distinguish between hemp and marijuana” since the former crop was legalized.

The complications resulting from hemp legalization became especially apparent in Texas, where marijuana possession arrests fell almost 30 percent from 2018 to 2019 following the state-level legalization of the non-intoxicating cannabis crop. Prosecutors in the state dismissed hundreds of low-level cannabis cases since hemp was legalized. And officials announced in 2020 that labs wouldn’t be performing testing in misdemeanor cases, with the Department of Public Safety saying it “will not have the capacity to accept those.”

Meanwhile, hemp industry stakeholders and agriculture officials across the U.S. are urging Congress to triple the THC limit for the crop to one percent by dry weight. A Justice Department researcher recently questioned the rationale for the current 0.3 percent THC limit, which she said seemed to be based arbitrarily on a decades-old anecdote.

USDA last month announced a new hemp “roadmap,” which includes a call for a public–private hemp consortium to streamline research into hemp products, and the agency also recently approved a new genetically modified version of hemp that does not produce THC or CBD but is designed to have higher levels of the cannabinoid CBG. It’s at least the second type of genetically modified hemp to get the OK after another modified plant, which produces lower levels of THC and CBC, was approved in October.

At the state level, meanwhile, observers have regularly found evidence of so-called lab-shopping by cannabis product manufacturers, wherein producers choose testing labs that provide more desirable results, such as inflated THC values for adult-use marijuana products, which buyers often choose based on perceived potency.

A study published last month found that Colorado marijuana products often overstate THC levels, with 70 percent of product labels reporting “percentages more than 15 percent higher than what was quantified through the lab.”

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Photo courtesy of National Institute of Standards and Technology.

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Ben Adlin, a senior editor at Marijuana Moment, has been covering cannabis and other drug policy issues professionally since 2011. He was previously a senior news editor at Leafly, an associate editor at the Los Angeles Daily Journal and a Coro Fellow in Public Affairs. He lives in Washington State.


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