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Cannabis Potency Testing: What’s in your weed?

by Kelly Tatera
Published: Jun 01, 2017   
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The demand for reliable cannabis testing is on the rise as more states legalize marijuana for medicinal and recreational purposes. 

Cannabis contains over 100 cannabinoids, of which tetrahydrocannabinol (THC), cannabidiol (CBD), and cannabinol (CBN) are often considered to be the most important when it comes to potency. Quantifying the different ratios of these cannabinoids is of interest to researchers and cannabis testing companies as they look to ensure the safety, efficacy, and characteristics of the cannabis in question. 

Cannabis testing tools 

There are several techniques that can be utilized for potency testing, most notably gas chromatography (GC), high-pressure liquid chromatography (HPLC), and near-infrared spectroscopy (NIRS). 

GC analysis enables scientists to separate and analyze compounds that can be vaporized without being decomposed.  

When it comes to cannabis analysis, however, GC can prove problematic. Due to the sample being vaporized under heat, some cannabinoids, such as Delta-9-Tetrahydrocannabinolic Acid (THCA) and Cannabidiolic acid (CBDA), undergo decarboxylation and convert to their non-acidic forms (THC and CBD respectively). Therefore, GC only enables measurement of total THC or CBD, as opposed to quantifying the precise amounts of different cannabinoids. These acidic forms are increasingly thought to have medical effects, different from those of THC and CBD. So, GC may not be the most effective way of profiling all of the active compounds accurately, particularly when the aim is to leverage the medicinal effects of the acidic forms of cannabinoids. 

Compared to GC, the main advantage of HPLC is that it does not require the sample to be heated at high temperatures, enabling both THC and THCA, as well as CBD/CBDA, to be measured individually.

“HPLC is the gold standard when it comes to measuring cannabis potency,” says Dr Bob Clifford, General Manager of Shimadzu Scientific Instruments. Clifford explains that HPLC is the best choice for potency analysis no matter what cannabis product is being tested —inflorescence, edibles, tinctures. etc.

According to NORML director Dale Gieringer and Dutch chemist Dr. Arno Hazekamp, GC and HPLC are by far the leading technologies for cannabis testing, but some analysts still opt for other methods, like NIRS. 

Steep Hill Labs, a global leader in cannabis testing, published a white paper on NIRS and cannabis analysis, arguing that the two seem to be a “natural fit.” A draw to NIRS analysis is that the technique, which is based on molecular overtone and combination vibrations, uses no polluting solvents and is at least 5 to 10 times quicker than wet methods with similar accuracy. 

Despite these benefits, “spectroscopy based methods such as NIRS can’t truly separate, identify, and quantify cannabinoids like that of HPLC,” Clifford notes. “NIRS-based systems are generally based on chemometric models and limited to THC, THCA, CBD, and CBDA. Deviation from the models can produce dramatically different results. For example, as new strains are analyzed, a new model will need to be created.”

A lack of cannabis testing standards 

As the marijuana industry is still in its infancy, many states don’t have solid regulations in place for cannabis analysis. Leafly published a breakdown of state-by-state cannabis testing regulations, and of the 28 states (and the District of Columbia) which have legalized medical marijuana, Colorado and Nevada are the only states that specifically mentioned potency analysis.

Colorado requires potency testing on dried and cured medical marijuana that is ready for sale, and the products fail the potency testing if they’re determined not to be homogenous.  According to Colorado’s code of regulations, a product is deemed non-homogenous if 10 percent of the infused portion of the marijuana product contains more than 20 percent of the THC content of the entire product.

Nevada’s Chapter 453A - Medical Use of Marijuana states that Nevada requires potency testing for a slew of marijuana products, including usable marijuana, marijuana extracts, edible marijuana products, liquid marijuana products, and topical marijuana-infused products. In fact, potency analysis is the only testing method required for all the specified marijuana product categories.

Michael Siebart, Managing Member of 374 Labs, an ISO 17025 accredited cannabis laboratory in Nevada, says that potency analysis is not a pass/fail test in Nevada. Instead of a safety test, potency analysis is used as “more of a descriptive test of what’s in there.” Like Clifford, Siebart says HPLC is better than GC for identifying the acidic cannabinoids and provides the best possible analysis of potency.

Testing without federal oversight 

Since marijuana remains a schedule I drug, alongside drugs like heroin and bath salts, there’s currently no federal oversight to cannabis regulation. This makes it almost impossible for researchers to establish standardized testing methods, as it’s left up to individual states, and even counties, to make regulatory decisions. As a result, there remains disagreements between different labs over which of the above-mentioned techniques is best for potency analysis.

Due to this regulatory grey area, users can’t rely on the government to implement proper analysis of cannabis products. “The patients need to be their own best advocates,” Kymron DeCesare, chief research officer at Steep Hill Labs, tells Lab Manager. “Always ask for the safety reports at a dispensary.”


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