The amount of THC in marijuana has been increasing steadily over the past ( especially the developing brain) are exposed to high concentrations of THC or. Cannabis potency, expressed as the Δ9-tetrahydrocannabinol (Δ9-THC; or THC) concentration over time has been the subject of occasional. 1d–f; see Methods for definition of total THC and CBD levels). .. Where THCA and THC refer to the percent dry weight concentration of each.
Data from most labs reflect the general pattern of hybrids having somewhat higher THC than indica and sativa, which are very similar. While commercial flower products fall into one of three chemotypes based on their THC: CBD ratios varied within and between the popular commercial strain names that flower samples are given.
Because the strain names of flower products submitted for laboratory testing are simply given by the producer-processor, they do not guarantee the true identity of the strain. In fact, personal correspondence with industry professionals indicated that we should expect flower samples submitted for testing to be mislabeled to some extent, perhaps due to business motives driving products to be given certain strain names based purely on their popularity and hence potential market value.
To visualize differences between samples based on their popular commercial strain names, we plotted the THC: This revealed clear differences in the THC: CBD ratios of samples labeled with different strain names.
Moreover, multi-modal distributions were apparent for many strains, with peaks sometimes at drastically different THC: Thus, for subsequent analyses, we quantified data before and after filtering by modal chemotype. THC-to-CBD ratios plotted on a logarithmic scale for cannabis flower samples across twenty-three popular commercial strain names for the single lab Lab A reporting the lowest a and the single lab Lab F reporting the highest b overall THC levels for cannabis flower.
To formalize how well colloquial strain names capture variation in THC: CBD profiles, we estimated a series of multilevel models with random intercepts for each strain 24 to estimate the share of the total variation in the logged THC: CBD ratio explained by the strain name, before and after filtering by modal chemotype.
This information is contained in the Intraclass Correlation Coefficient ICC , a measure of similarity within-groups calculated as the ratio of the within-strain variance to the total variance see Methods. When using tail values, results with zero reported CBD were coerced to a ratio of 3. These values correspond approximately to the most extreme values observed in the data see Fig. Results shown for the lab reporting the lowest mean THC levels.
Across all labs, the pre-filtered strain ICC was 0. After filtering, the ICCs increase, respectively, to about 0. This overall test conceals significant variation between labs.
In general, a large portion of the variation in THC: CBD ratio was attributable to strain name. Labs varied substantially in the proportion of zero CBD test results, and, consequently, the ICC was more sensitive to the handling of missing data for those labs.
Given these observations, we compared total THC and CBD levels across strains only after filtering data by laboratory and modal chemotype. Using data from only one laboratory ensured that the same laboratory testing protocol was used to measure cannabinoids across flower samples. We chose to use data from Lab A, which had the largest number of flower samples. These results suggest that strain names can provide meaningful, though variable, signals of the composition of flower samples.
Furthermore, the strength of this signal varies between labs, particularly with respect to the CBD content of high-THC flower. Our results confirm that commercial cannabis strains in Washington fall into three principal chemotypes defined by their THC: CBD ratio, similar to landrace 13 and commercial Dutch strains While this result is unsurprising given the biological constraints on cannabinoid production 25 , 26 , we were able to use this dataset to investigate outstanding questions about commercial cannabis products widely used by consumers today.
These included formal analysis of discrepancies in the cannabinoid levels reported by different laboratories, trends in THC content over time, and systematic differences in the THC: CBD profiles between flower samples with different labeled strain names.
A key area of concern for legal cannabis consumers, industry professionals, and state regulators is the accuracy of the state-mandated testing data that is required to be displayed on product packaging. Our analyses revealed clear, systematic differences in the results obtained by different testing facilities in Washington, with some labs consistently reporting higher or lower levels of cannabinoids than others. Moreover, these differences could not be explained by differences in the producer or strain name associated with the samples being submitted, suggesting that discrepancies between labs are likely caused by systematic differences in their testing methodologies.
It is crucial that precise standards are adopted by the industry to ensure that laboratories produce results that are reproducible across labs, independent of the exact testing method used, with the ultimate goal of reporting results that consumers can trust. The results reported by labs with lower median THC levels are in better agreement with independent measurements of cannabis flower from legal markets 8 , 28 , For example, Vergara et al.
Reliable cannabis laboratory testing is an attainable goal. In the absence of federal regulations in the United States for the foreseeable future, it will be incumbent on state regulators to implement universal testing standards for cannabis laboratories. But states have extensive experience in this arena, regulating laboratories that analyze drinking water and evidence from crime scenes. They need only hold cannabis laboratories to similar standards.
A first step may be to require that cannabis labs, like other testing facilities, receive third-party accreditation of compliance with International Organization for Standardization ISO guidelines for testing and calibration laboratories by auditors who are themselves ISO-accredited Second, states could require that cannabis labs adhere to a standardized testing protocol for analyzing cannabis to ensure consistency between labs.
Such protocols have already been developed. For example, the American Herbal Pharmacopoeia published a page monograph called Cannabis Inflorescence detailing analytical procedures for cannabinoid detection and quantification to establish benchmark methods While it is well-known that modern recreational cannabis contains higher levels of THC than it did in previous decades 17 , this apparent plateauing in recent years may be expected due to biological limits imposed on cannabinoid production.
In general, our results do not suggest that flower samples labeled as indica, sativa, and hybrid differ substantially in terms of total THC content or THC: Samples labeled sativa vs. However, we did find that hybrid strains have slightly higher levels of total THC. Since hybrid strains are produced by crossing indica and sativa varieties, this result is somewhat counterintuitive. We interpret it as potentially owing to the selective breeding of hybrid strains to maximize THC content for commercial purposes.
It is also possible that, on average, these group are grown under different growing conditions, such as indoors vs. It remains possible that indica and sativa samples differ systematically in their full phytocannabinoid or terpene profile. Indeed, a recent analysis of cannabinoid and terpene profiles from Dutch flower samples found several terpenes that may serve as markers for indica- vs.
Other recent work 23 has shown how more complete sets of biochemical measurements, including terpenoid profiles, can be used to define multiple distinct Cannabis chemovars. Since flower samples with different strain names within each of the three principal chemotypes can be differentiated somewhat by their THC: CBD ratio, more detailed analysis of the biochemical composition of commercial strains may uncover further differences.
An important area of future research will be to define the chemovars for commercially available cannabis products in legal U.
Applying computational approaches to large-scale cannabinoid and terpene datasets will allow cannabis strains and products to be organized according to their biochemical constituents rather than colloquial strain names.
However, doing so requires having accurate lab testing data in the first place, which requires the establishment of laboratory testing standards that ensure the correct identification and quantification of the contents of cannabis products.
Our results highlight the need for such standards given the large, systematic differences observed between laboratories in Washington. We submitted public records requests for all test results registered with the Washington State Liquor and Cannabis Board LCB , the agency which regulates cannabis sales.
The request was made on August 7, and the LCB provided us the raw data files on August 14, The data files from which we extracted data for our analyses are attached online. We focused our analyses on two product categories: We encourage other scholars to mine this dataset for further insights. The Indica, Sativa, or Hybrid categorization from Leafly. Our data matched to 1, unique commercial strains. The popularity of consumer strain names were determined by cumulative pageviews of the strain pages on Leafly.
The matching process had two stages. If the two algorithms agreed, then the test result was assigned the Leafly strain. Through this process, used to minimize the number of false positive matches, , A complete list of raw strain names and their corresponding Leafly match can be found in the Supplementary Information files. Following previous scholars 13 , test results were classified into chemotypes based on the distinct groups visible after plotting the log 10 THC-to-CBD ratio.
For our analyses, we defined chemotype I strains as any with a 5: Due to the size of the I dataset we analyzed, statistical comparisons often involved samples with tens of thousands of data points each, and statistically significant results were often achieved even for trivial differences between sample means with highly overlapping distributions.
Thus, we calculated effect size in a variety of ways to determine whether differences between samples were relatively large or small. When comparing continuous distributions, we computed effect size in two ways: Performing a t-test to measure a difference in the means Similarly, the CL effect size is 0.
The effect size matrices displayed in this paper allow one to assess whether differences between samples are relatively large or small, which is especially useful when large sample sizes allow small differences to reach statistical significance.
Each of the four regression models shown employed a fixed-effect transformation for each grower-strain combination to absorb heterogeneity in cannabinoid content attributable to these factors Written in the Least Squares Dummy Variable formulation, each equation takes the form:. As a robustness check, for regressions subsetted to concentrate products, an additional dummy variable for type of concentrate e.
Standard errors were clustered by grower-strain, since the number of clusters is large there were 22, grower-strain combinations and residuals are likely to be correlated within clusters To examine clustering in THC: CBD ratio by strain name, we estimated unconditional two-level hierarchical models with random intercepts for each strain, across all labs and separately by lab.
Each specification took the following form:. The Intraclass Correlation Coefficient ICC is calculated as the ratio of the within-group variance to the total variance, which can be decomposed into the within-group variance and the between group variance.
Regression was used to estimate whether indica, sativa, and hybrid flower products differed systematically in THC and CBD. Standard errors were clustered by strain, since indica, sativa, hybrid is a strain-level property. There were 1, unique strains. All data generated or analyzed during this study are included in this published article and its Supplementary Information files.
They are also available in the Harvard Data Repository The authors would like to thank Dr. Brad Douglass and Dr. David Roberson for helpful comments and feedback on the manuscript.
Nick Jikomes is employed by Leafly Holdings, Inc. Neither Leafly nor Privateer have a direct financial interest in any third-party laboratory testing facilities in the legal cannabis industry.
Nick Jikomes and Michael Zoorob contributed equally to this work. Supplementary information accompanies this paper at Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. National Center for Biotechnology Information , U. Published online Mar Nick Jikomes 1 and Michael Zoorob 2.
Nick Jikomes 1 Leafly Holdings, Inc. Author information Article notes Copyright and License information Disclaimer. Received Jan 6; Accepted Feb To view a copy of this license, visit http: This article has been cited by other articles in PMC.
Abstract The majority of adults in the U. Introduction For millennia, Cannabis has been cultivated for medicinal, recreational, and industrial purposes 1. Open in a separate window. Interlab Differences Persist After Controlling for Plausible Confounds To investigate potential determinants of interlab differences, we quantified the average cannabinoid levels reported by each lab after accounting for strain name, the producer-processor submitting samples for testing, and time of measurement see Methods.
Low-level cannabinoid measurements vary widely across laboratories Examination of THC: Discussion Our results confirm that commercial cannabis strains in Washington fall into three principal chemotypes defined by their THC: Chemotype Cutoffs Following previous scholars 13 , test results were classified into chemotypes based on the distinct groups visible after plotting the log 10 THC-to-CBD ratio.
Statistical Significance and Effect Size for Very Large Samples Due to the size of the I dataset we analyzed, statistical comparisons often involved samples with tens of thousands of data points each, and statistically significant results were often achieved even for trivial differences between sample means with highly overlapping distributions.
Cannabinoid Inflation Regression Models Each of the four regression models shown employed a fixed-effect transformation for each grower-strain combination to absorb heterogeneity in cannabinoid content attributable to these factors Written in the Least Squares Dummy Variable formulation, each equation takes the form: Each specification took the following form: Data Availability Statement All data generated or analyzed during this study are included in this published article and its Supplementary Information files.
Electronic supplementary material Supplemental Figures K, pdf. Supplementary Dataset 1 52M, csv. Acknowledgements The authors would like to thank Dr. Footnotes Nick Jikomes and Michael Zoorob contributed equally to this work.
Electronic supplementary material Supplementary information accompanies this paper at History of Cannabis as a Medicine. Whiting PF, et al. Cannabinoids for medical use: A systematic review and meta-analysis. Cannabis drug testing describes various drug test methodologies for the use of cannabis in medicine, sport, and law. Cannabis use is highly detectable and can be detected by urinalysis , hair analysis , as well as saliva tests for days or weeks.
Unlike alcohol, for which impairment can be reasonably measured using a breathalyser and confirmed with a blood alcohol content measurement , valid detection for cannabis is time-consuming, and tests cannot determine an approximate degree of impairment. The lack of suitable tests and agreed-upon intoxication levels is an issue in the legality of cannabis , especially regarding intoxicated driving.
The concentrations obtained from such analyses can often be helpful in distinguishing active use from passive exposure, elapsed time since use, and extent or duration of use. The Duquenois-Levine test is commonly used as a screening test in the field, but it cannot definitively confirm the presence of cannabis, as a large range of substances have been shown to give false positives.
Most cannabinoids are lipophilic fat soluble compounds that easily store in fat, thus yielding a long elimination half-life relative to other recreational drugs.
The THC molecule, and related compounds, are usually detectable in urine drug tests from 3 days up to 10 days according to Redwood Laboratories; heavy users can produce positive tests for 1—3 months after ceasing cannabis use. Marijuana use can be detected up to 3—5 days after exposure for infrequent users; for heavy users: However, every individual is different, and detection times can vary due to metabolism or other factors.
It also depends on whether actual THC or THC metabolites are being tested for, the latter having a much longer detection time than the former. Drugs which may be present in the urine specimen compete against their respective drug conjugate for binding sites on their specific antibody. During testing, a urine specimen migrates upward by capillary action. A drug, if present in the urine specimen below its cut-off concentration, will not saturate the binding sites of its specific antibody.
The antibody will then react with the drug-protein conjugate and a visible colored line will show up in the test line region of the specific drug strip. False positives have been known to be triggered by consuming hemp-seed bars and other products, although the more detailed, more expensive gas chromatography-mass spectrometer GCMS test can tell the difference.
In , researchers at John Jay College of Criminal Justice reported that dietary zinc supplements can mask the presence of THC and other drugs in urine. Similar claims have been made in web forums on that topic. Common known pharmaceutical drugs which cause false positives in instant THC dip tests include: To administer the test, a police officer simply has to break a seal on a tiny micropipette of chemicals, and insert a particle of the suspected substance; if the chemicals turn purple, this indicates the possibility of marijuana.
But the color variations can be subtle, and readings can vary by examiner. It was adopted in the s by the United Nations as the preferred test for cannabis. The dyes, as water-soluble salts, are typically applied during thin layer chromatography.
They are extremely sensitive to a variety of cannabinoids, and very specific in reaction. Due to concerns about Fast Blue B being carcinogenic Fast Blue BB is often used instead,  although it too is a suspected carcinogen. Beam discovered that the tissue of hemp , which is typically low in THC but high in CBD, gives a purple color when treated with bases.
Cannabis use is detectable with hair tests and is generally included in the standard hair test. Hair tests generally take the most recent 1. That provides a detection period of approximately 90 days. The detection window for body hair cannabis testing will be longer, because body hair grows slower than head hair and distorts the detection timeframe.
Hair drug testing measures the marijuana parent metabolite embedded inside the hairshaft and eliminates external contamination as a source of a positive result. Cannabis is detectable by saliva testing. Just like blood testing, saliva testing detects the presence of parent drugs and not their inactive metabolites.
This results in a shorter window of detection for cannabis by saliva testing. If a saliva sample is tested in a lab, the detection level can be as low as 0.
A Rise in Marijuana’s THC Levels
How much THC or CBD does your favorite cannabis product contain? Learn different ways you can estimate levels of these cannabinoids in products. THC attaches to these receptors and activates them and affects a person's memory, pleasure, movements, thinking, concentration, coordination. "We've seen potency values close to 30 percent THC, which is huge. “Although the rise in the concentration of THC is not a concern per se.