An Overview of Testing Capabilities to Identify Use of Marijuana (THC) and Other Natural Cannabinoids

Clinical Update
December 2023

An Overview of Testing Capabilities to Identify Use of Marijuana (THC) and Other Natural Cannabinoids

Following the passing of the 2018 Agriculture Improvement Act (a.k.a. Farm Bill), the cannabis industry has seen widespread growth in products that contain naturally occurring cannabinoids found in the Cannabis sativa plant.   Aegis has expanded its marijuana analysis to include delta-8 THC and cannabidiol (CBD) for the purpose of providing a more informed assessment of patient use of cannabinoids.  The information provided in this clinical update is intended to assist providers with understanding testing for naturally occurring cannabinoids at Aegis, how positive test results will be reported, and information related to CBD and delta-8 THC products. Concerns such as period of detection, oral fluid considerations, and passive inhalation are also discussed.  Expanded cannabinoid analysis is currently only available in urine.

Cannabis Overview

The Cannabis sativa plant contains over 500 compounds, at least 100 of which are cannabinoids, the most prevalent and widely studied being delta-9-THC (THC) and CBD.1 Hemp and marijuana are two varieties of Cannabis sativa and differ in THC content with hemp containing 0.3% THC or less by dry weight.  Marijuana is the most commonly used federally illicit drug in the United States.  The 2020 National Survey on Drug Use and Health reported that 59.3 million people aged 12 or older used illicit drugs in the past year, with 49.6 million (~84%) using marijuana.2 In the 2021 National Survey on Drug Use and Health, 38.1 million people aged 18 or older used illicit drugs in the past month with 34.8 million (~91%) using marijuana.3 In addition to being the most commonly used illicit substance, marijuana use has been increasing with decriminalization and/or legalization occurring in a growing number of states.  The National Institute on Drug Abuse reported that in 2021, the proportion of adults aged 19-30 surveyed that reported past year marijuana use was 43%, up from 29% in 2011.4  For adults aged 35 to 50 surveyed in 2022, percentages of those reporting use within the past year was 28%, up from 13% in 2012.5 Daily marijuana use also increased with 11% of young adults surveyed in 2021 reporting daily use compared to 6% in 2011.4  Marijuana is the drug with the highest prevalence in cases involving driving under the influence of drugs and the source of more positive results in workplace drug tests than any other drug of abuse.6

THC is the main psychoactive component in Cannabis Sativa and is responsible for the characteristic “high” of marijuana, whereas CBD has not been shown to have the same cognitive effects and is considered non-psychoactive. While THC is the most prevalent cannabinoid in cannabis plants grown for the purpose of psychoactive product development, CBD is the most abundant cannabinoid in hemp plants.  It has been studied as a treatment for multiple disease states and health conditions, including bipolar mania, Huntington’s disease, inflammation, insomnia, multiple sclerosis, nausea, social anxiety disorder, schizophrenia, and seizures. Through the passing of the 2018 Agriculture Improvement Act, hemp was no longer considered a controlled substance in the USA, resulting in a burgeoning market of hemp-derived products having CBD as the predominant ingredient.

Recently other cannabinoids, such as delta-8 THC, have been found in a variety of commercially available products including liquids used for electronic cigarettes (i.e, vapes), edibles, and drinks.  Like THC, delta-8 THC is a psychoactive cannabinoid of the Cannabis sativa plant.  Delta-8 THC is nearly identical to THC in chemical structure, differing only in the placement of a double bond.  Both THC and delta-8 THC have similar binding affinities at CB1 and CB2 cannabinoid receptors7-8 and produce similar effects with the psychotropic potency of delta-8 THC being estimated to be approximately two-thirds that of THC.9 A recent survey of delta-8 THC users suggests delta-8 THC produces the same experiential effects as THC but with less cognitive distortion and distressing mental states such as paranoia and anxiety, than THC.10  Delta-8 THC is not present in the Cannabis sativa plant in significant amounts.  The percentage of delta-8 THC in cannabis plant material was determined to be on average 0.65% with a maximum observed percentage of 3%.11 In a recent study, urine samples containing the THC metabolite delta-9 carboxy-THC were evaluated for the presence of the delta-8 THC metabolite, delta-8 carboxy-THC, which was detected in low concentrations (0.22-8.9 ng/mL), presumably from plant origin.  The average percentage of delta-8 carboxy-THC to delta-9 carboxy-THC observed was 0.68% and ranged from 0.05 to 2.83%.12 

Presumptive (i.e. Immunoassay) vs. Definitive Testing

The interpretation of cannabinoid results differs when considering presumptive vs. definitive testing methods and may also differ among laboratories.  At Aegis, testing for marijuana use proceeds through immunoassay screening.  When non-negative immunoassay results are obtained, then the specimen will proceed to definitive confirmatory testing using mass spectrometry.  Specimens that produce a negative cannabinoid immunoassay result are considered negative and will not be tested further.  Immunoassay screening is based on cross-reactivity to a target drug.  Drugs similar in structure to the target drug may cross-react to produce a non-negative or presumptive positive result.  Delta-8 and THC isomers, being nearly identical in chemical structure, are not able to be distinguished by cannabinoid immunoassay tests.  Delta-8 THC and THC share the same metabolic pathways.13  Thus as delta-9 carboxy-THC is the main metabolite for THC in urine, delta-8 carboxy-THC is the main metabolite for delta-8 THC in urine.12  Recent studies have demonstrated that delta-8 THC and its metabolites cross-react with commercially available cannabinoid immunoassay tests.14,15  Specifically, delta-8 carboxy-THC produced a high degree of cross-reactivity (87-112%) across different commercially available cannabinoid immunoassay platforms at a 50 ng/mL cutoff.  This high degree of cross reactivity was also observed at 20 and 100 ng/mL cutoffs.15 Thus delta-8 THC use is likely to produce a non-negative cannabinoid immunoassay test result.  Conversely, CBD did not cross-react with any of the commercially available cannabinoid immunoassay tests.14  Thus Aegis testing is not intended to be used to determine compliance with CBD-containing medications (i.e. Epidolex®) or use of CBD products.  CBD-containing medications are not able to be indicated as prescribed.

Confirmatory testing using chromatography/mass spectrometry may not be able to distinguish between the delta-8 carboxy-THC and delta-9 carboxy-THC isomers unless they are separated in the test method.15  Laboratories have reported an increasing number of specimens with interferences in testing for delta 9-THC due to the presence of delta 8-THC.15-17  At Aegis, prior to reporting positive test results for naturally occurring cannabinoids including THC, delta-8 THC and CBD, analysis proceeds through definitive confirmatory testing by liquid chromatography tandem mass spectrometry (LC-MS/MS).  Results of positive findings for delta-8 carboxy-THC, delta-9 carboxy-THC, and CBD will be reported individually (see Figure 1).  Concentrations of these cannabinoids, when detected in urine, do not definitively indicate source of substance used or exposure that contributed to positive findings and will not be reported with interpretative differentiations. 

Figure 1.



Marijuana False Positives on Immunoassay

Immunoassay, or point of care testing, has the highest risk of false positives among all testing methods.18 The following medications and over-the-counter products have chemical structures similar enough to THC to trigger a presumptive positive result that would not confirm via LC-MS/MS on an Aegis test: Acetylsalicylic acid, baby wash/soaps19, efavirenz18,20, NSAIDs (ibuprofen, naproxen)21-22, proton pump inhibitors (pantoprazole)18,23, tolmetin24, and more.

Marijuana False Negatives on Immunoassay

People using marijuana may attempt to tamper with urine samples to produce negative results. Addition of Visine® eyedrops to urine samples has been shown to cause false-negative results for THC. Chemical analysis of Visine® eyedrops has shown that the ingredients, benzalkonium chloride and the borate buffer, can directly decrease the concentration of the delta-9 carboxy-THC metabolite in the urine with no effects on the antibodies in the immunoassay. However, these ingredients do not chemically alter delta 9-carboxy-THC, which will still be detected by mass spectrometry.22,25  Excess fluid ingestion has been shown to produce false-negative urine test results for delta-9 carboxy-THC metabolite.26

CBD Products

Since the passing of the 2018 Agriculture Improvement Act, there has been a burgeoning market of hemp-derived products having CBD as the predominant ingredient. The product descriptions “medical marijuana”, “high CBD,” and “low THC” are often used interchangeably, however no standard definition exists for these individual terms.27 The legal limit for the amount of THC allowed in CBD products is variable, ranging from 0.3% to 5% depending on state-specific regulations.28 Importantly, the manufacturing and purification processes for CBD products are not regulated by the Food and Drug Administration (FDA), leaving little opportunity for mandated CBD to THC ratios to be enforced.27-28 In a study evaluating label accuracy of CBD products, 54% of products tested contained CBD concentrations within ±10% of the ingredient label claim, 15% contained <90% of the label claim with the lowest being 17%, and 31% contained >110% of the label claim, the highest being 159%.29  A few studies have evaluated urinary cannabinoids following administration of CBD and CBD-dominant cannabis.27,30,31 After dosing 15 volunteers with high CBD/low THC oils, capsules, and cigarettes, fourteen of the fifteen volunteers tested positive for both CBD and delta-9 carboxy-THC in urine.27 Following vaporized and oral administration of 100 mg CBD, and vaporized administration of CBD-dominant (100 mg CBD/3.7 mg THC) cannabis, delta-9 carboxy-THC was > 15 ng/mL in 2 of 6 individuals between 4 and 8 hours only following administration of CBD-dominant cannabis.30 In an expansion of this study, of 12 additional participants, only one was positive for delta-9 carboxy-THC at >15 ng/mL following vaporized administration of CBD-dominant cannabis.31  All of the specimens with delta-9 carboxy-THC >15 ng/mL, screened positive by immunoassay with a cutoff of 20 ng/mL.31  Another study evaluated urinary delta-9 carboxy-THC concentrations in 14 individuals following a 4 week administration of a high CBD product.  Of the 14 participants, 50% screened positive and 6 were confirmed by mass spectrometry to have delta-9 carboxy-THC concentrations > 15 ng/mL, with the highest concentration being 71.5 ng/mL.32  THC content varies among unregulated hemp and cannabidiol products; the ability of these products to cause a positive marijuana result will depend on the amount of THC present in the product, the amount and frequency of the ingestion, and individual patient pharmacokinetics.33-35  Given these factors, it is possible for the use of a CBD product to result in a THC-positive urine drug test. It is vital that healthcare providers use caution when recommending or reviewing CBD products for patients due to little regulation and inaccurate labeling of quantities within products.36  Prescription CBD (Epidolex®) was developed to contain negligible amounts of THC (<0.1%)37; thus, it is unlikely to cause a marijuana positive.38

Delta-8-Tetrahydrocannabinol (delta-8 THC) Products

Although delta-8 THC is present in low abundance in the cannabis plant, it may be readily synthesized from CBD.  Recently delta-8 THC products such as gummies and vapes are available over-the counter with some being marketed as “legal hemp” products.  Due to the naturally low levels of delta-8 THC in hemp it is thought that delta-8 THC is being synthesized from CBD and added to hemp plant material in high concentrations that far exceed what is naturally found in cannabis and then sold as “legal hemp”.8 There has been confusion regarding the legal status of such products because tetrahydrocannabinols, natural or synthetic, are classified as controlled in schedule I by the Controlled Substances Act (CSA).  However, the CSA excludes from control tetrahydrocannabinols in hemp.  Some states are choosing to define delta-8 THC as a controlled substance and others are prohibiting production and sale of delta-8 THC.  It is important to note that like CBD products, some delta-8 THC products may contain THC and are not regulated by the FDA.39-40  Thus depending on the amount of THC present in the product, the amount and frequency of the ingestion, and individual patient pharmacokinetics, it may be possible for the use of a delta-8 THC product to result in a THC-positive urine drug test.  The content and labeling of twenty commercial delta-8 THC products has been evaluated.  The only cannabinoids identified in the products were delta-8 THC, THC and CBD.40 THC was detected in 35% of the delta-8 THC products and CBD was detected in one product.40  A recent study determined the prevalence of delta-8 carboxy-THC in specimens submitted for workplace drug testing reported 24% of all cannabinoid-positive specimens were consistent with use of a delta-8 THC product, alone or in combination with cannabis.41 For samples with a positive immunoassay test result (cutoff 50 ng/mL) and concentrations of delta-8 carboxy-THC and delta-9 carboxy-THC less than but equal to 15 ng/mL, 123 (˜10%) contained delta-8 carboxy-THC only, 889 (˜70%) contained delta-9 carboxy-THC only and 255 (˜20%) contained both delta-8 carboxy-THC and delta 9-carboxy-THC.60 Ratios were variable with 76% of specimens having <10% delta-8 carboxy-THC, 11% having >90% delta-8 carboxy-THC, and 13% were fairly evenly distributed across all other ratios between 10 and 90 but with somewhat more in the 10-20% delta-8 carboxy-THC range.41 

Period of Detection Considerations

The detection time for delta-9 carboxy-THC in urine depends heavily on the body composition of the patient and the frequency of use. Daily use of marijuana is expected to be detectable in urine for a period up to 10 days; light use (such as one joint) may only be detectable for up to 3 days.42  One study demonstrated that 73% of 37 chronic marijuana users had  delta-9 carboxy-THC concentrations below a cutoff of 15 ng/mL within two weeks of last ingestion.43  Patients with a large amount of adipose tissue and/or those with heavy use over a chronic period may store marijuana and excrete metabolites for a longer period of time. In such cases, marijuana has been reported with a period of detection up to 30 days, with the longest period published as 95 days. Such a period of detection is the exception, not the rule.18,42,44  During terminal elimination of delta 9-carboxy-THC, consecutive urine specimens may fluctuate between positive and negative as delta-9 carboxy-THC concentrations near the cutoff.45 Normalization of urinary concentrations may facilitate interpretation of consecutive urine drug concentrations.45

Due to structural similarity between delta-8 carboxy-THC and delta 9-carboxy-THC, the period of detection of delta-8 carboxy-THC in urine may be similar to that of delta 9-carboxy-THC.  Urinary excretion of CBD was evaluated following a single administration of 100 mg of CBD by different routes of administration and with different formulations.31  CBD concentrations in urine were highly variable even within the same route of administration and formulation.  For example, following vaporized administration of cannabis (100 mg CBD/3.7 mg THC), maximum concentrations of CBD in urine ranged from 27-808 ng/mL.  In a few participants, specimens were >15 ng/mL for only few hours whereas other individual’s last specimen >15 ng/mL was the 21-25 hour collection.31 The authors concluded the data show that absorption and elimination of CBD is impacted by drug formulation, route of administration and gastric contents.31

Oral Fluid Considerations

Marijuana positives in oral fluid are generally due to a depot effect after smoking, which limits interpretation to recent use.46 Using a 2 ng/mL threshold, detection times in oral fluid for last positive following smoking of a single 6.8% THC cigarette, in frequent and occasional smokers were 30 and 26 hours respectively.47  Median detection times in frequent and occasional smokers was 21 and 13.5 hours respectively with earliest last positives being at 6 and 5 hours respectively.47 In a placebo-controlled double-blinded randomized trial in which frequent and occasional users self-titrated while smoking 5.9 or 13.4% THC cannabis, THC in oral fluid was detectable >2 ng/mL in 74% of users at the study duration of 6 hours.48  Maximum concentration of THC in oral fluid is greater following inhaled routes such as smoking and vaporization than after oral cannabis.49 Oral ingestion of THC produces lower and later peak blood concentrations and effects than smoked THC, and only 6-20% of an orally administered dose reaches systemic circulation.50-51 An increase in THC oral fluid concentrations was observed following oral dosing of a THC-containing brownie whereas that was not observed following administration of encapsulated synthetic oral THC (dronabinol).49-50 Ingestion of dronabinol (Marinol®) is unlikely to cause a positive test for THC in oral fluid at a 2 ng/mL threshold, which is used at Aegis.50 Using oral fluid as a specimen type may, therefore, be beneficial when assessing patients who claim to ingest Marinol® to explain marijuana positives in urine.

Passive Inhalation

A common issue that confuses the interpretation for marijuana testing is “passive inhalation.” The argument presented is that exposure to marijuana smoke by a non-user will result in a positive urine cannabinoid test, and therefore, a person will be wrongfully accused of drug use. Historically, multiple studies were performed in the 1980s that demonstrated that passive exposure to marijuana in extreme conditions did sometimes result in positive delta-9 carboxy-THC in urine.52-56  In the study by Cone et al. which reported concentrations obtained by chromatography/mass spectrometry methods, positive results were found under repeated exposure or exposure conditions so extreme that the study subjects were offered goggles to wear in order to prevent eye and mucous membrane irritation due to the test area being visibly saturated with marijuana smoke. Anecdotal evidence of study subjects who had taken off their goggles concluded that prolonged exposure would be unlikely to be tolerable to most subjects.55 Most of the studies were conducted in unventilated areas (closed cars or specifically built rooms of small size). Furthermore, Cone et al. conducted a test of room air THC exposure levels in the same test room as their studies with ventilation, which resulted in THC levels <10% that of the room unventilated.55

One criticism of studies conducted in prior decades is that marijuana is available at increased potency today, which could influence drug test results. More recent studies conducted to investigate urinary concentrations of carboxy-THC following passive exposure include Rohrich et al. where subjects were exposed to marijuana smoke for three hours in a Netherlands coffee shop. Urinary concentrations of delta-9 carboxy-THC were no greater than 5 ng/mL (without hydrolysis) or 8 ng/mL (with hydrolysis).57 A second study performed by Cone et al. evaluated passive exposure using high-potency marijuana (11.3%) being smoked by six smokers for one hour in the presence of six non-smokers in unventilated and ventilated conditions.58 The researchers demonstrated that with ventilation consistent with typical air conditioning, some study subjects did excrete detectable delta 9-carboxy-THC.  The maximum concentration observed in a non-smoker with unventilated conditions was 57 ng/mL, whereas with ventilated conditions the maximum was 15 ng/mL, both occurring at 4-6 hours following exposure.58

Cone et al. also researched the likelihood of positive oral fluid results under similar conditions as above. Maximum oral fluid concentrations of THC were present in non-smokers up to 308 ng/mL in unventilated conditions and 75 ng/ mL in ventilated conditions.59 Maximum concentrations occurred immediately post exposure and dropped rapidly within 1-3 hours, with subjects in unventilated conditions testing below 2 ng/mL after 12 hours, and subjects in ventilated conditions after 2 hours. During the unventilated studies, smoke accumulation was rapid, and goggles were used to alleviate eye irritation, whereas ventilated sessions produced visible smoke at lower levels. Niedbala et al. measured THC in oral fluid following passive exposure to marijuana for 20 minutes in an unventilated van with four smokers and found THC concentrations did not exceed 1.2 ng/mL following exposure, with all specimens below 2 ng/mL. Urine concentrations of delta-9 carboxy-THC were also assessed and did not exceed 15 ng/mL.60 Moore et al. measured THC in oral fluid following less extreme exposure in a Dutch coffee shop. Oral fluid specimens collected outside the coffee shop during exposure reached a maximum THC concentration of 17 ng/mL at 3 hours; in specimens collected 12-22 hours following exposure THC was either not present or less than 2 ng/mL.61  Passive inhalation of marijuana is also unlikely to cause a positive test in oral fluid at typical laboratory thresholds, except in circumstances of heavy smoke exposure, long duration of exposure, lack of ventilation, and if exposure occurs on the same day as sample collection.58,60

Overall, the likelihood of positive marijuana results from passive inhalation will depend on the amount and duration of exposure, ventilation during exposure, and time since exposure. In circumstances of true passive inhalation, levels of THC (oral fluid) or delta-9 carboxy-THC (urine) would be expected to be low, and the exposure would have occurred very recent to the time of collection.  Due to structural similarity between delta-8 carboxy-THC and delta-9 carboxy-THC, the possibility of positive delta-8 carboxy-THC results following passive inhalation may be similar to that of delta-9 carboxy-THC.


Please call our clinical scientists at 1-877-552-3232 if you require additional information.


NOTICE: The information above is intended as a resource for health care providers. Providers should use their independent medical judgment based on the clinical needs of the patient when making determinations of who to test, what medications to test, testing frequency, and the type of testing to conduct.




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