For a patient, knowing a strain's total THC and CBD content ― the two main compounds responsible for everything from pain relief to making Zeppelin that much cooler ― is important; when you're trying to find helpful strains, their chemical makeup is a more useful tool than looking for crystal-covered leaves.
Analytical testing methods have been used in more cannabis-tolerant countries in Europe, as well as in California, for some time now, and give a general idea of what the range of active THC and CBD percentages can be in marijuana. THC, for example, might range from under 0.3 percent in industrial hemp to nearly 30 percent in high-end medicinal strains, according to a United Nations report. Internet sites and glossy magazines like High Times regularly post test results showing THC content in the mid- to high 20s along with their connoisseur-quality ganja photos.
But how accurate are the THC percentages that shops tout to lure in patients? For starters, the plant material tested by the dispensaries may not be the same as what you're taking home in a jar. Unlike pharmaceutical medicine, where levels of chemical compounds are regulated, marijuana buds rely on a much more natural system. Due to environmental factors, the top buds the shop sends to be tested may have more resin glands than the bottom buds in the jars on the shelves. Different crops can also produce different levels of THC, so that buds of OG Kush pulled down in December might be stronger than buds pulled down in August, when temperatures were higher in the grow room and plants were more stressed. Such changes are common knowledge among dispensary owners and growers.
What isn't common knowledge is why the accuracy of the tests themselves can vary so much. Shopping at Native Roots a few months ago, I was given a disclaimer along with test results indicating that the dispensary's LifeSaver Strain was 22 percent THC. "The test results are good," the budtender told me, "but it doesn't really mean much." Owner Rhett Jordan later noted that the same strain had tested at 14 percent THC earlier: "It was a different crop, but still, there shouldn't be a huge fluctuation of the thing."
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Other shops have seen even more variance. In 2009, Denver Relief took first place in five out of six categories ― including smell, appearance and potency ― at the Medical Marijuana Harvest Cup in Fort Collins with its cross of Sour Diesel and Sensi Star called Bio Diesel. So a few months later, when the shop had the strain tested for the first time through Full Spectrum Laboratories, owners were floored by results that showed a 15 percent THC content. Six months later, the shop had the strain tested again at Full Spectrum; this time, it came back at 25.51 percent THC. If both tests were accurate, the results showed that the second crop of Bio Diesel grown from the same mother plant, in what the grower said were nearly identical conditions, was 67 percent more potent.
Buckie Minor, spokesman for Full Spectrum, says the company has used the same growing methods since it started roughly three years ago; he attributes the huge increase in potency to either how the strain was grown or where the samples were taken from on the plant. (Interestingly, he says Full Spectrum has seen Colorado herb in general increasing in potency over the past year. "I don't know a single grower that hasn't changed in the last year," he notes. "We did some see things in the higher teen numbers more often, but hitting in the 20s was very rare.")
Since states leave the regulation of medicine to the federal government and the Federal Drug Administration doesn't recognize marijuana as a medicine, there are no procedural standards for testing marijuana potency in this country; each laboratory is left to devise what it thinks is the best way to determine results. Colorado laboratories use three main methods to test a strain's potency: high performance liquid chromatography (HPLC), gas chromatography and thin-layer chromatography. All three separate the elements of a sample and test for amounts of specific compounds left behind; these amounts are compared to a known quantity of THC, called a standard.
To see how much variation there was between lab tests, we gave nearly identical samples of Killer Queen to four testing facilities: RM3 Labs in Boulder; Genovations Creations in Colorado Springs; and Herbal Synergy LLC and Full Spectrum, both in Denver. Most agreed that we should expect a variance of roughly 3 percentage points. Here are the results:
RM3 labs (tested with thin-layer chromatography): 23.0 percent THC Owner Ian Barringer wasn't surprised that his results came out the highest, given his method of removing all of the stem (and sometimes seeds) from the bud. Not everyone does this, he says; some labs simply grind the bud stem into the solvent. The system is left up to each lab, which helps account for the wide range of results.
Genovations Creations (HPLC): 14.24 percent THC The lowest percentage came from Genovations Creations, which also provided the least-detailed results. The only information we received was the total percentage of THC and THC-acid content by weight of the product. According to John Kopta, chief science officer at Genovations, variations from test to test could be due to a number of things, ranging from the quality of the standards to the sample given to the lab.
Herbal Synergy (gas chromatography): 15.54 percent THC Herbal Synergy owner Charlie Steinberg uses a portable GC machine the size of a typical rolling suitcase to do on-site testing. He conducted our test in the kitchen of his Capitol Hill apartment, calibrating his machine to a national standard provided by a third party.
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Full Spectrum Labs (HPLC): 17.22 percent THC Full Spectrum's results came close to a statistical average of the other three: 17.22 percent THC (the average is 17.84 percent). According to Minor, his company uses the most accurate HPLC method ― one also preferred by the Dutch, long known for their friendly take on cannabis use.
Denver Relief conducted a similar test using its Bio Diesel strain at the same labs in October. The variation ranged from 17.15 percent THC from Genovations to 17.95 percent THC from Herbal Synergy to Full Spectrum's 28.8 percent THC -- 13 percent more potent than the last set of results from the same batch of Bio Diesel tested in August. For Denver Relief, this experiment just proved what the center's owners and others have long suspected: Without a standard in the industry, a test's accuracy is up to the method used, the person administering it -- and the pot.
This isn't to say that testing doesn't have its benefits. Each lab we spoke with said the ratio of THC to other cannabinoids should remain the same from test to test, regardless of what the actual levels of the compounds read out to be; that information can help patients pinpoint the strains best suited for their conditions. But next time you see a shop advertising some amazingly high THC content for its herb, take those claims with a grain of kief.
A version of this story appeared in the most recent issue of The Chronic-le, a quarterly Westword publication devoted to medical marijuana. Watch for the next edition of The Chronic-le on May 19. To read more about MMJ in Colorado, go to our Marijuana archives.