Intra- and intersubject whole blood/plasma cannabinoid ratios determined by 2-dimensional, electron impact GC-MS with cryofocusing

Effect of vaporizing cannabis rich in cannabidiol on cannabinoid levels in blood and on driving ability - a randomized clinical trial

The aim of this prospective, placebo-controlled, double-blind, randomized, cross-over study was to determine cannabinoid levels in blood and driving-related ability after single (S1) and repetitive (S2) vaporization of cannabis rich in cannabidiol (CBD) containing < 1% Δ9-etrahydrocannabinol (THC). Healthy adult volunteers (Nsingle = 27, Nrepetitive = 20) with experience in smoking vapor-inhaled two low-THC/CBD-rich cannabis products both with < 1% THC (product 1: 38 mg CBD, 1.8 mg THC; product 2: 39 mg CBD, 0.6 mg THC) and placebo. Main outcomes were THC- and CBD-levels in whole blood and overall assessment of driving-related ability by computerized tests. Among 74 participants included, 27 (mean age ± SD, 28.9 ± 12.5 years) completed S1, and 20 (25.2 ± 4.0) completed S2. Peak concentrations and duration of detectability depended on the THC-content of the product. After single consumption THC dropped below 1.5 µg/L after 1.5 h, but was detected in some participants up to 5 h. Pairwise comparison of driving-related ability revealed no significant differences between low-THC/CBD-rich products (P1, P2) and placebo. Detection of THC after consumption of low-THC/CBD-rich cannabis might have legal consequences for drivers. Regarding overall driving-related ability, no significant differences were observed between the interventional products. This trial was registered with the German Clinical Trials Register (DRKS00018836) on 25.10.2019 and with the Coordination Office for Human Research (kofam) which is operated by the Federal Office of Public Health (FOPH) (SNCTP000003294).

Variable Delta-9-Tetrahydrocannabinol Pharmacokinetics and Pharmacodynamics After Cannabis Smoking in Regular Users

BACKGROUND

Despite its federally restricted status, cannabis is widely used medicinally and recreationally. The pharmacokinetics (PK) and central nervous system (CNS) effects of tetrahydrocannabinol (THC), the major psychoactive cannabinoid, are not well understood. The objective of this study was to develop a population PK model of inhaled THC, including sources of variability, and to conduct an exploratory analysis of potential exposure-response relationships.

METHODS

Regular adult cannabis users smoked a single cannabis cigarette containing 5.9% THC (Chemovar A) or 13.4% THC (Chemovar B) ad libitum. THC concentrations in whole blood were measured and used to develop a population PK model to identify potential factors contributing to interindividual variability in THC PK and to describe THC disposition. Relationships between model-predicted exposure and heart rate, change in composite driving score on a driving simulator, and perceived highness were evaluated.

RESULTS

From the 102 participants, a total of 770 blood THC concentrations were obtained. A two-compartment structural model adequately fit the data. Chemovar and baseline THC (THC BL ) were found to be significant covariates for bioavailability, with Chemovar A having better THC absorption. The model predicted that heavy users-those with the highest THC BL -would have significantly higher absorption than those with lighter previous use. There was a statistically significant relationship between exposure and heart rate, and exposure and perceived highness.

CONCLUSIONS

THC PK is highly variable and related to baseline THC concentrations and different chemovars. The developed population PK model showed that heavier users had higher THC bioavailability. To better understand the factors affecting THC PK and dose-response relationships, future studies should incorporate a wide range of doses, multiple routes of administration, and different formulations relevant to typical community use.

GC vs. HPLC in quantitation of CBD, CBG, ∆9-THC and CBN in plasma using different sample preparation methods

The sensitivity of complex analytical procedures depends not only on the sensitivity of the analytical instrument used, but also on the recovery degree of the examined analyte by the employed sample preparation method. The recovery degrees of individual cannabinoids reported in literature, estimated using the same sample preparation method, are unexpectedly divergent. Therefore, the aim of this study was a thorough assessment of the most commonly used sample preparation methods, such as protein precipitation, LLE, QuEChERS and SPE, in the context of the reliability of the obtained results. The presented report shows that the highest sensitivity, precision and reliability of the chromatographic analysis of CBG, CBD, ∆9-THC and CBN in human plasma can be obtained using SPE. The recovery degrees of these cannabinoids by SPE are highly repeatable and exceed 95 %, while they are significantly lower for such sample preparation methods as protein precipitation, LLE and QuEChERS (ca. 80, 65 and 87, respectively). Moreover, the supernatants obtained by the latter methods contain interferents evoking matrix-effect, which makes reliable quantification of the listed cannabinoids by GC difficult. To our knowledge, the paper is the first such extensive comparison of sample preparation procedures used for the determination of cannabinoids in plasma by GC-MS and HPLC-MS. The presented results and the discussion allow to understand why different recovery degrees for the same xenobiotic can be find in literature despite they have been estimated using the same or different sample preparation method or different chromatography types.

Objective Identification of Cannabis Use Levels in Clinical Populations Is Critical for Detecting Pharmacological Outcomes

Introduction: Cannabis is widely used for recreational and medical purposes, but its therapeutic efficacy remains unresolved for many applications as data from retrospective studies show dramatic discrepancy. We hypothesized that false self-reporting of cannabis use and lack of differentiation of heavy users from light or occasional users contribute to the conflicting outcomes. Objective: The goal of this study was to develop an objective biomarker of cannabis use and test how application of such biomarker impacts clinical study outcomes and dose-response measures. Methods and Analysis: Population pharmacokinetic (PK) models of (-)-trans-Δ9-tetrahydrocannabinol (THC) and its metabolites 11-hydroxy-Δ9-tetrahydrocannabinol (11-OH-THC) and 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (11-COOH-THC) were developed based on published studies reporting cannabinoid disposition in individual subjects following intravenous administration or smoking of cannabis. Plasma 11-COOH-THC concentration distributions in different cannabis user groups smoking cannabis were generated via Monte Carlo simulations, and plasma concentration cutoff values of 11-COOH-THC were developed to differentiate light and heavy daily cannabis users in clinical studies. The developed cutoff value was then applied to a retrospective study that assessed the impact of cannabis use on T cell activation in subjects with HIV who self-reported as either nonuser or daily user of cannabis. Results: The developed population PK models established plasma 11-COOH-THC concentration of 73.1 μg/L as a cutoff value to identify heavy daily users, with a positive predictive value of 80% in a mixed population of equal proportions of once daily and three times a day users. The stratification allowed detection of changes in T cell activation in heavy users which was not detected based on self-reporting or detectability of plasma cannabinoids. A proof-of-concept power analysis demonstrated that implementation of such cutoff value greatly increases study power and sensitivity to detect pharmacological effects of cannabis use. Conclusions: This study shows that the use of plasma 11-COOH-THC concentration cutoff value as an objective measure to classify cannabis use in target populations is critical for study sensitivity and specificity and provides much needed clarity for addressing dose-response relationships and therapeutic effects of cannabis.

Pain response to cannabidiol in opioid-induced hyperalgesia, acute nociceptive pain, and allodynia using a model mimicking acute pain in healthy adults in a randomized trial (CANAB II)

ABSTRACT

Opioids in general and remifentanil in particular can induce hyperalgesia. Preclinical data suggest that cannabidiol might have the capacity to reduce opioid-induced hyperalgesia (OIH). Thus, we investigated the effect of oral cannabidiol on OIH in healthy volunteers using an established pain model. Twenty-four healthy participants were included in this randomized, double-blinded, crossover study and received either a 1600-mg single-dose oral cannabidiol or placebo. Hyperalgesia, allodynia, and pain were induced by intracutaneous electrical stimulation. To provoke OIH, participants recieved an infusion of 0.1 µg/kg/min remifentanil over a time frame of 30 minutes, starting 100 minutes after oral cannabidiol ingestion. The primary outcome was the area of hyperalgesia (in square centimetres) up to 60 minutes after remifentanil administration. The area of allodynia (in square centimetres) and pain (numeric rating scale) were also assessed.Cannabidiol had no significant effect on hyperalgesia, allodynia, or pain at any time point of measurement compared with placebo. The area of hyperalgesia after remifentanil administration significantly increased compared with baseline (17.0 cm 2 [8.1-28.7] vs 25.3 cm 2 [15.1-39.6]; P = 0.013). Mean cannabidiol blood levels were 4.1 ± 3.0 µg/L (mean ± SD) at 130 minutes after ingestion and were 8.2 μg/L ± 6.9 µg/L (mean ± SD) at 200 minutes. Cannabidiol was well tolerated. We conclude that a high single-oral dose of 1600-mg cannabidiol is not effective in reducing OIH. Before excluding an effect of cannabidiol on OIH, research should focus on drug formulations enabling higher cannabidiol concentrations.

Oleamide as analyte protectant in GC analysis of THC and its metabolites in blood

Methods for the analysis of cannabinoids in bio-matrices are continually being developed, to achieve a proper sensitivity required for their detection and accuracy in their quantification. The presented paper shows that the analytical sensitivity of GC-MS to THC and its metabolites in blood samples can be significantly increase by oleamide (OLA) addition to the examined sample, which evokes the matrix effect of transient character. The magnitude of signal increment resulting from oleamide presence in the examined sample is the greatest for THC metabolites and depends on oleamide concentration in the examined sample. The use of transient matrix effect to increase the sensitivity of the analysis can be applied not only in QuEChERS procedure, which is applied in the described experiments, but also in other blood sample preparation methods. Evoking the transient matrix effect by means of OLA in the experimental analytical quantitation of THC and its metabolites in blood allowed to lower limit of detection (LOD) approximately by 20.5%, 87.6% and 90.1% in the case of THC, THC-OH and THC-COOH, respectively.

The blood-to-plasma ratio and predicted GABAA-binding affinity of designer benzodiazepines

PURPOSE

The number of benzodiazepines appearing as new psychoactive substances (NPS) is continually increasing. Information about the pharmacological parameters of these compounds is required to fully understand their potential effects and harms. One parameter that has yet to be described is the blood-to-plasma ratio. Knowledge of the pharmacodynamics of designer benzodiazepines is also important, and the use of quantitative structure-activity relationship (QSAR) modelling provides a fast and inexpensive method of predicting binding affinity to the GABA_A receptor.

METHODS

In this work, the blood-to-plasma ratios for six designer benzodiazepines (deschloroetizolam, diclazepam, etizolam, meclonazepam, phenazepam, and pyrazolam) were determined. A previously developed QSAR model was used to predict the binding affinity of nine designer benzodiazepines that have recently appeared.

RESULTS

Blood-to-plasma values ranged from 0.57 for phenazepam to 1.18 to pyrazolam. Four designer benzodiazepines appearing since 2017 (fluclotizolam, difludiazepam, flualprazolam, and clobromazolam) had predicted binding affinities to the GABA_A receptor that were greater than previously predicted binding affinities for other designer benzodiazepines.

CONCLUSIONS

This work highlights the diverse nature of the designer benzodiazepines and adds to our understanding of their pharmacology. The greater predicted binding affinities are a potential indication of the increasing potency of designer benzodiazepines appearing on the illicit drugs market.

Pain response to cannabidiol in induced acute nociceptive pain, allodynia, and hyperalgesia by using a model mimicking acute pain in healthy adults in a randomized trial (CANAB I)

ABSTRACT

Preclinical studies have demonstrated the analgesic potential of cannabidiol (CBD). Those suggesting an effect on pain-processing receptors have brought CBD back into focus. This study assessed the effect of CBD on acute pain, hyperalgesia, and allodynia compared with placebo. Twenty healthy volunteers were included in this randomized, placebo-controlled, double-blinded, crossover study assessing pain intensities (using numeric rating scale), secondary hyperalgesia (von Frey filament), and allodynia (dry cotton swab) in a well-established acute pain model with intradermal electrical stimulation. The authors compared the effect of 800-mg orally administered CBD on pain compared with placebo. They further examined the effect on hyperalgesia and allodynia. Cannabidiol whole blood levels were also measured. Pain ratings (mean ± SD) did not differ significantly after CBD application compared with placebo (5.2 ± 0.7 vs 5.3 ± 0.7, P-value 0.928), neither did the areas of hyperalgesia and allodynia differ significantly after CBD application compared with placebo (hyperalgesia 23.9 ± 19.2 cm2 vs 27.4 ± 17.0 cm2, P-value 0.597; allodynia 16.6 ± 13.1 cm2 vs 17.3 ± 14.1 cm2, P-value 0.884). The CBD whole blood level (median, first to third quartile) was 2.0 µg/L (1.5-5.1) 60 minutes and 5.0 µg/L (4.0-10.4) 130 minutes after CBD application. Although the oral application of 800-mg CBD failed to show a significant effect, it is important to focus future research on different dosing, routes of administration, and CBD as a part of multimodal treatment strategies before negating its effects on acute pain.

Preliminary Eye-Tracking Data as a Nonintrusive Marker for Blood Δ-9-Tetrahydrocannabinol Concentration and Drugged Driving

Background: Cannabis is one of the drugs most often found in drivers involved in serious motor vehicle collisions. Validity and reliability of roadside cannabis detection strategies are questioned. This pilot study aimed to investigate the relationship between eye characteristics and cannabis effects in simulated driving to inform potential development of an alternative detection strategy. Materials and Methods: Multimodal data, including blood samples, eye-tracking recordings, and driving performance data, were acquired from 10 participants during a prolonged single-session driving simulator experiment. The study session included a baseline driving trial before cannabis exposure and seven trials at various times over ∼5 h after exposure. The multidimensional eye-tracking recording from each driving trial for each participant was segmented into nonoverlapping epochs (time windows); 34 features were extracted from each epoch. Blood Δ-9-tetrahydrocannabinol (THC) concentration, standard deviation of lateral position (SDLP), and mean vehicle speed were target variables. The cross-correlation between the temporal profile of each eye-tracking feature and target variable was assessed and a nonlinear regression analysis evaluated temporal trend of features following cannabis exposure. Results: Mean pupil diameter (r=0.81-0.86) and gaze pitch angle standard deviation (r=0.79-0.87) were significantly correlated with blood THC concentration (p<0.01) for all epoch lengths. For driving performance variables, saccade-related features were among those showing the most significant correlation (r=0.61-0.83, p<0.05). Epoch length significantly affected correlations between eye-tracking features and speed (p<0.05), but not SDLP or blood THC concentration (p>0.1). Temporal trend analysis of eye-tracking features after cannabis also showed a significant increasing trend (p<0.01) in saccade-related features, including velocity, scanpath, and duration, as the influence of cannabis decreased by time. A decreasing trend was observed for fixation percentage and mean pupil diameter. Due to the lack of placebo control in this study, these results are considered preliminary. Conclusion: Specific eye characteristics could potentially be used as nonintrusive markers of THC presence and driving-related effects of cannabis. clinicaltrials.gov (NCT03813602).

Pharmacokinetics of Mephedrone and Its Metabolites in Whole Blood and Plasma after Controlled Intranasal Administration to Healthy Human Volunteers

Mephedrone is a popular synthetic cathinone, known for its psychostimulant effects. At present, there is no data available on the pharmacokinetics of mephedrone and its metabolites in concurrently collected whole blood and plasma samples after a controlled intranasal administration to healthy volunteers. In this study, six healthy male volunteers nasally insufflated 100 mg of pure mephedrone hydrochloride (Day 1). Whole blood and plasma samples were collected at different time points after the administration and were analyzed for the presence of mephedrone and its metabolites, dihydro-mephedrone (DHM), nor-mephedrone (NOR), hydroxytolyl-mephedrone (HYDROXY), 4-carboxy-mephedrone (4-CARBOXY) and dihydro-nor-mephedrone (DHNM), by validated liquid chromatography-tandem mass spectrometry methods. All analytes were detected in whole blood and plasma for 6 h post administration, with mephedrone and NOR also being detectable on Day 2 in some participants. 4-CARBOXY, followed by NOR, was the most abundant metabolite in both matrices. Compared to other psychostimulants, mephedrone showed rapid absorption (mean Tmax of 52.5 ± 20.7 min in plasma and 55.0 ± 18.2 min in whole blood) and elimination (mean t1/2 of 1.98 ± 0.30 h in plasma and 2.12 ± 0.33 h in whole blood). In addition, statistical analysis showed that median whole blood to plasma distribution ratios, reported here for the first time, were statistically different from 1 (unity) for mephedrone (median: 1.11), DHM (median: 1.30) and NOR (median: 0.765). It is hoped that the study will aid forensic and clinical toxicologists in detection, identification and interpretation of cases associated with mephedrone use.

Development and Verification of a Linked Δ 9-THC/11-OH-THC Physiologically Based Pharmacokinetic Model in Healthy, Nonpregnant Population and Extrapolation to Pregnant Women

Conducting clinical trials to understand the exposure risk/benefit relationship of cannabis use is not always feasible. Alternatively, physiologically based pharmacokinetic (PBPK) models can be used to predict exposure of the psychoactive cannabinoid (-)-Δ⁹-tetrahydrocannabinol (THC) and its active metabolite 11-hydroxy-Δ⁹-tetrahydrocannabinol (11-OH-THC). Here, we first extrapolated in vitro mechanistic pharmacokinetic information previously quantified to build a linked THC/11-OH-THC PBPK model and verified the model with observed data after intravenous and inhalation administration of THC in a healthy, nonpregnant population. The in vitro to in vivo extrapolation of both THC and 11-OH-THC disposition was successful. The inhalation bioavailability (F_inh) of THC after inhalation was higher in chronic versus casual cannabis users (F_inh = 0.35 and 0.19, respectively). Sensitivity analysis demonstrated that 11-OH-THC but not THC exposure was sensitive to alterations in hepatic intrinsic clearance of the respective compound. Next, we extrapolated the linked THC/11-OH-THC PBPK model to pregnant women. Simulations showed that THC plasma area under the curve (AUC) does not change during pregnancy, but 11-OH-THC plasma AUC decreases by up to 41%. Using a maternal-fetal PBPK model, maternal and fetal THC serum concentrations were simulated and compared with the observed THC serum concentrations in pregnant women at term. To recapitulate the observed THC fetal serum concentrations, active placental efflux of THC needed to be invoked. In conclusion, we built and verified a linked THC/11-OH-THC PBPK model in healthy nonpregnant population and demonstrated how this mechanistic physiologic and pharmacokinetic platform can be extrapolated to a special population, such as pregnant women. SIGNIFICANCE STATEMENT: Although the pharmacokinetics of cannabinoids have been extensively studied clinically, limited mechanistic pharmacokinetic models exist. Here, we developed and verified a physiologically based pharmacokinetic (PBPK) model for (-)-Δ⁹-tetrahydrocannabinol (THC) and its active metabolite, 11-hydroxy-Δ⁹-tetrahydrocannabinol (11-OH-THC). The PBPK model was verified in healthy, nonpregnant population after intravenous and inhalation administration of THC, and then extrapolated to pregnant women. The THC/11-OH-THC PBPK model can be used to predict exposure in special populations, predict drug-drug interactions, or impact of genetic polymorphism.

An evaluation of postmortem concentrations of Δ9-tetrahydrocannabinol (THC) and 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THCCOOH)

Δ9-tetrahydrocannabinol (THC), the primary psychoactive component of cannabis, leads to impaired cognitive and psychomotor function resulting in an increased risk of fatal motor vehicle collisions and other traumas resulting in death. It is important to measure cannabinoids in postmortem cases to improve understanding of this growing public safety issue. However, postmortem concentrations of THC and its primary inactive metabolite, 11-nor-9-carboxy-tetrahydrocannabinol (THCCOOH), have not been extensively studied. We aim to further characterize postmortem concentrations of THC and THCCOOH in peripheral blood with and without preservation, central blood, and central "serum" to support improved forensic interpretation. Cannabinoids were extracted from blood and "serum" from twenty-five decedents using solid phase extraction followed by quantification using gas chromatography - mass spectrometry. We evaluated the impact of sample preservation, reported central blood-to-peripheral blood (CB:PB) ratios and blood-to-"serum" ratios, and assessed the relationship of CB:PB and postmortem interval for THC and THCCOOH. Correlations of preserved compared to unpreserved blood were strong with r² > 0.97. The median CB:PB ratios were 1.1 and 1.3 for THC and THCCOOH, respectively. THCCOOH CB:PB was significantly higher than 1.0 (p-value < 0.001). The CB:PB ratio was only weakly correlated with PMI for both compounds. The median blood-to-"serum" ratio was 1.0 for THC and 0.8 for THCCOOH. The blood-to-"serum" ratio of THCCOOH was significantly lower than 1.0 (p-value < 0.001). Results demonstrated minimal potential for postmortem redistribution of THC and THCCOOH and that the ratio of blood-to-"serum" in postmortem samples differs from the blood-to-plasma ratio established in living humans. Based on these results, it is not recommended to apply a correction factor to THC and THCCOOH concentrations from postmortem blood samples. Our study improves the understanding of postmortem cannabinoid concentrations to support forensic interpretation in cases of fatal motor vehicle accidents.

Predicting the Potential for Cannabinoids to Precipitate Pharmacokinetic Drug Interactions via Reversible Inhibition or Inactivation of Major Cytochromes P450

Cannabis is used for both recreational and medicinal purposes. The most abundant constituents are the cannabinoids - cannabidiol (CBD, nonpsychoactive) and (-)-trans-Δ⁹-tetrahydrocannabinol (THC, psychoactive). Both have been reported to reversibly inhibit or inactivate cytochrome P450 (CYPs) enzymes. However, the low aqueous solubility, microsomal protein binding, and nonspecific binding to labware were not considered, potentially leading to an underestimation of CYPs inhibition potency. Therefore, the binding-corrected reversible (IC_50,u) and irreversible (K _I,u ) inhibition potency of each cannabinoid toward major CYPs were determined. The fraction unbound of CBD and THC in the incubation mixture was 0.12 ± 0.04 and 0.05 ± 0.02, respectively. The IC_50,u for CBD toward CYP1A2, 2C9, 2C19, 2D6, and 3A was 0.45 ± 0.17, 0.17 ± 0.03, 0.30 ± 0.06, 0.95 ± 0.50, and 0.38 ± 0.11 µM, respectively; the IC_50,u for THC was 0.06 ± 0.02, 0.012 ± 0.001, 0.57 ± 0.22, 1.28 ± 0.25, and 1.30 ± 0.34 µM, respectively. Only CBD showed time-dependent inactivation (TDI) of CYP1A2, 2C19, and CYP3A, with inactivation efficiencies (k _inact/K _I,u) of 0.70 ± 0.34, 0.11 ± 0.06, and 0.14 ± 0.04 minutes^-1 µM^-1, respectively. A combined (reversible inhibition and TDI) mechanistic static model populated with these data predicted a moderate to strong pharmacokinetic interaction risk between orally administered CBD and drugs extensively metabolized by CYP1A2/2C9/2C19/2D6/3A and between orally administered THC and drugs extensively metabolized by CYP1A2/2C9/3A. These predictions will be extended to a dynamic model using physiologically based pharmacokinetic modeling and simulation and verified with a well-designed clinical cannabinoid-drug interaction study. SIGNIFICANCE STATEMENT: This study is the first to consider the impact of limited aqueous solubility, nonspecific binding to labware, or extensive binding to incubation protein shown by cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC) on their true cytochrome P450 inhibitory potency. A combined mechanistic static model predicted a moderate to strong pharmacokinetic interaction risk between orally administered CBD and drugs extensively metabolized by CYP1A2, 2C9, 2C19, 2D6, or 3A and between orally administered THC and drugs extensively metabolized by CYP1A2, 2C9, or 3A.

A patient-centric liquid chromatography-tandem mass spectrometry microsampling assay for analysis of cannabinoids in human whole blood: Application to pediatric pharmacokinetic study

Medical cannabis is increasingly used for the treatment of various ailments in children and adults. Three major cannabinoids in cannabis are delta-9-tetrahydrocannabinol (THC), cannabidiol (CBD), and cannabinol (CBN). There is a growing need to develop and utilize a patient-centric blood microsampling methodology to enable clinical trials and facilitate therapeutic drug monitoring. We have employed the volumetric absorptive microsampling (VAMS™) devices that enables accurate and precise collection of a fixed volume (20 µL) of blood, minimizing the impact of hematocriton accurate quantitation. We developed an ultra-performance liquid chromatographic method with tandem mass spectrometry detection for the quantification of three cannabinoids (THC, CBD, and CBN) employing deuterium labelled internal standards (THC-D₃, CBD-D₃, and CBN-D₃). Sample extraction of VAMS™ devices, followed by solid phase extraction, reverse phase chromatographic separation, and selective detection using tandem mass spectrometry with a 6-minute runtime per sample was developed. Standard curves were linear between 1 and 500 ng/mL for THC and 0.5-500 ng/mL for CBD and CBN. Intra-day accuracies were within 91.3-112% while inter-day accuracies were within 94.4-107% with both having precisions (CV (%)) of <13% based on quality control samples in a three day validation study for all three cannabinoids. Analytes were stable in human whole blood under assay conditions (60 h at room temperature and 24 h in autosampler post-extraction). Dried microsamples were stable for one week at 40 °C, two weeks (15 days) under different storage conditions (room temperature, 4, -20 and -78 °C), one month (29 days) at -20 and -78 °C and three months (68 days) at -78 °C. This assay provides an efficient quantitation of THC, CBD, and CBN in VAMS™ devices and is currently being implemented for pediatric clinical trials.

A marijuana-drug interaction primer: Precipitants, pharmacology, and pharmacokinetics

In the United States, the evolving landscape of state-legal marijuana use for recreational and/or medical purposes has given rise to flourishing markets for marijuana and derivative products. The popularity of these products highlights the relative absence of safety, pharmacokinetic, and drug interaction data for marijuana and its constituents, most notably the cannabinoids. This review articulates current issues surrounding marijuana terminology, taxonomy, and dosing; summarizes cannabinoid pharmacology and pharmacokinetics; and assesses the drug interaction risks associated with co-consuming marijuana with conventional medications. Existing pharmacokinetic data are currently insufficient to fully characterize potential drug interactions precipitated by marijuana constituents. As such, increasing awareness among researchers, clinicians, and federal agencies regarding the need to conduct well-designed in vitro and clinical studies is imperative. Mechanisms that help researchers navigate the legal and regulatory barriers to conducting these studies would promote rigorous evaluation of potential marijuana-drug interactions and inform health care providers and consumers about the possible risks of co-consuming marijuana products with conventional medications.

Current Technologies of Electrochemical Immunosensors: Perspective on Signal Amplification

An electrochemical immunosensor employs antibodies as capture and detection means to produce electrical charges for the quantitative analysis of target molecules. This sensor type can be utilized as a miniaturized device for the detection of point-of-care testing (POCT). Achieving high-performance analysis regarding sensitivity has been one of the key issues with developing this type of biosensor system. Many modern nanotechnology efforts allowed for the development of innovative electrochemical biosensors with high sensitivity by employing various nanomaterials that facilitate the electron transfer and carrying capacity of signal tracers in combination with surface modification and bioconjugation techniques. In this review, we introduce novel nanomaterials (e.g., carbon nanotube, graphene, indium tin oxide, nanowire and metallic nanoparticles) in order to construct a high-performance electrode. Also, we describe how to increase the number of signal tracers by employing nanomaterials as carriers and making the polymeric enzyme complex associated with redox cycling for signal amplification. The pros and cons of each method are considered throughout this review. We expect that these reviewed strategies for signal enhancement will be applied to the next versions of lateral-flow paper chromatography and microfluidic immunosensor, which are considered the most practical POCT biosensor platforms.

Plasma Cannabinoid Pharmacokinetics After Controlled Smoking and Ad libitum Cannabis Smoking in Chronic Frequent Users

More Americans are dependent on cannabis than any other illicit drug. The main analytes for cannabis testing include the primary psychoactive constituent, Δ(9)-tetrahydrocannabinol (THC), equipotent 11-hydroxy-THC (11-OH-THC) and inactive 11-nor-9-carboxy-THC (THCCOOH). Eleven adult chronic frequent cannabis smokers resided on a closed research unit with unlimited access to 5.9% THC cannabis cigarettes from 12:00 to 23:00 during two ad libitum smoking phases, followed by a 5-day abstinence period in seven participants. A single cigarette was smoked under controlled topography on the last day of the smoking and abstinence phases. Plasma cannabinoids were quantified by two-dimensional gas chromatography-mass spectrometry. Median plasma maximum concentrations (Cmax) were 28.3 (THC), 3.9 (11-OH-THC) and 47.0 μg/L (THCCOOH) 0.5 h after controlled single cannabis smoking. Median Cmax 0.2-0.5 h after ad libitum smoking was higher for all analytes: 83.5 (THC), 14.2 (11-OH-THC) and 155 μg/L (THCCOOH). All 11 participants' plasma samples were THC and THCCOOH-positive, 58.3% had THC ≥5 μg/L and 79.2% were 11-OH-THC-positive 8.1-14 h after last cannabis smoking. Cannabinoid detection rates in seven participants 106-112 h (4-5 days) after last smoking were 92.9 (THC), 35.7 (11-OH-THC) and 100% (THCCOOH), with limits of quantification of 0.5 μg/L for THC and THCCOOH, and 1.0 μg/L for 11-OH-THC. These data greatly expand prior research findings on cannabinoid excretion profiles in chronic frequent cannabis smokers during ad libitum smoking. Smoking multiple cannabis cigarettes led to higher Cmax and AUC compared with smoking a single cigarette. The chronic frequent cannabis smokers exhibited extended detection windows for plasma cannabinoids, reflecting a large cannabinoid body burden.

Extended plasma cannabinoid excretion in chronic frequent cannabis smokers during sustained abstinence and correlation with psychomotor performance

Cannabis smoking increases motor vehicle accident risk. Empirically defined cannabinoid detection windows are important to drugged driving legislation. Our aims were to establish plasma cannabinoid detection windows in frequent cannabis smokers and to determine if residual cannabinoid concentrations were correlated with psychomotor performance. Twenty-eight male chronic frequent cannabis smokers resided on a secure research unit for up to 33 days with daily blood collection. Plasma specimens were analyzed for Δ(9) -tetrahydrocannabinol (THC), 11-hydroxy-THC (11-OH-THC), and 11-nor-9-carboxy-THC (THCCOOH) by gas chromatography-mass spectrometry. Critical tracking and divided attention tasks were administered at baseline (after overnight stay to ensure lack of acute intoxication) and after 1, 2, and 3 weeks of cannabis abstinence. Twenty-seven of the twenty-eight participants were THC-positive at admission (median 4.2 µg/L). THC concentrations significantly decreased 24 h after admission, but were still ≥2 µg/L in 16 of the 28 participants 48 h after admission. THC was detected in 3 of 5 specimens on day 30. The last positive 11-OH-THC specimen was 15 days after admission. THCCOOH was measureable in 4 of 5 participants after 30 days of abstinence. Years of prior cannabis use significantly correlated with THC concentrations on admission, and days 7 and 14. Tracking error, evaluated by the Divided Attention Task, was the only evaluated psychomotor assessment significantly correlated with cannabinoid concentrations at baseline and day 8 (11-OH-THC only). Median THC was 0.3 µg/L in 5 chronic frequent cannabis smokers' plasma samples after 30 days of sustained abstinence. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Analysis of Δ9-tetrahydrocannabinol driving under the influence of drugs cases in Colorado from January 2011 to February 2014

Driving under the influence (DUI) and DUI drugs (DUID) law enforcement (LE) cases (n = 12,082) where whole blood samples were submitted to ChemaTox Laboratory, Inc. in Boulder, CO, for testing were examined. Of these 12,082 cases, there were 4,235 cannabinoid screens (CS) requested. Samples that yielded a positive CS (n = 2,621) were further analyzed. A total of 1,848 samples were confirmed for Δ9-tetrahydrocannabinol (THC) after a positive CS. Due to a decrease in the confirmation limit of detection (LOD) for THC from 2 to 1 ng/mL, samples that were confirmed for THC and quantitated below 2 ng/mL (n = 250) were considered negative. After this normalization, there were 1,598 samples that were confirmed positive for THC and included in the analysis. The percentage of LE cases with requests for CS for all years was 35%, increasing from 28% in 2011 to 37% in 2013. The positivity rate of CS overall was 62% (range: 59-68% by year) with no significant change over the time frame examined. The percentage of positive CS in which THC was confirmed positive at or above 2 ng/mL (n = 1,598) increased significantly from 28% in 2011 to 65% in 2013. The mean and median THC concentrations were 8.1 and 6.3 ng/mL, respectively (range: 2-192 ng/mL, n = 1,367). The data presented illustrate a statistically significant increase in CS that result in positive THC confirmations. Although the specific cause of this increase is not known at this time, possible ties to ongoing developments in Colorado's marijuana legislation merit further analysis.

In vitro stability of free and glucuronidated cannabinoids in blood and plasma following controlled smoked cannabis

BACKGROUND

Blood and plasma cannabinoid stability is important for test interpretation and is best studied in authentic rather than fortified samples.

METHODS

Low and high blood and plasma pools were created for each of 10 participants after they smoked a cannabis cigarette. The stabilities of Δ(9)-tetrahydrocannabinol (THC), 11-hydroxy-THC (11-OH-THC), 11-nor-9-carboxy-THC (THCCOOH), cannabidiol (CBD), cannabinol (CBN), THC-glucuronide, and THCCOOH-glucuronide were determined after 1 week at room temperature; 1, 2, 4, 12, and 26 (±2) weeks at 4 °C; and 1, 2, 4, 12, 26 (±2), and 52 (±4) weeks at -20 °C. Stability was assessed by Friedman test.

RESULTS

Numbers of THC-glucuronide and CBD-positive blood samples were insufficient to assess stability. In blood, 11-OH-THC and CBN were stable for 1 week at room temperature, whereas THC and THCCOOH-glucuronide decreased and THCCOOH increased. In blood, THC, THCCOOH-glucuronide, THCCOOH, 11-OH-THC, and CBN were stable for 12, 4, 4, 12, and 26 weeks, respectively, at 4 °C and 12, 12, 26, 26, and 52 weeks at -20 °C. In plasma, THC-glucuronide, THC, CBN, and CBD were stable for 1 week at room temperature, whereas THCCOOH-glucuronide and 11-OH-THC decreased and THCCOOH increased. In plasma, THC-glucuronide, THC, THCCOOH-glucuronide, THCCOOH, 11-OH-THC, CBN, and CBD were stable for 26, 26, 2, 2, 26, 12, and 26 weeks, respectively, at 4 °C and 52, 52, 26, 26, 52, 52, and 52 weeks, respectively, at -20 °C.

CONCLUSIONS

Blood and plasma samples should be stored at -20 °C for no more than 3 and 6 months, respectively, to assure accurate cannabinoid quantitative results.

Silver nanowire-based electrochemical immunoassay for sensing immunoglobulin G with signal amplification using strawberry-like ZnO nanostructures as labels

The quick development of nanoscience and nanotechnology has paved the way for ultrasensitive biosensing and analysis. In this work, an ultrasensitive electrochemical immunosensor was developed for the detection of human immunoglobulin G (IgG) by combining with a newly designed trace tag on a disposable immunosensor array. The array was prepared by immobilizing captured antibodies on ultralong Ag nanowires, whilst the trace tag was prepared by loading horseradish peroxidase (HRP)-labeled goat anti-human IgG (HRP-anti-IgG) on thionine (TH)-doped mesoporous ZnO nanostrawberries (MP-ZnO). With a sandwich-type immunoassay format, mainly due to crystalline framework and high surface area of the mesoporous (MP) materials, as well as the superconductivity of silver nanowires, the electrochemical signal was significantly amplified. The linear range of the developed immunosensor is 0.01-200 ng mL(-1) and the detection limit is 4 pg mL(-1) IgG, which make the hierarchically nanostructured composites very promising candidates for the next-generation sandwich-type electrochemical immunoassays.

Predictive model accuracy in estimating last Δ9-tetrahydrocannabinol (THC) intake from plasma and whole blood cannabinoid concentrations in chronic, daily cannabis smokers administered subchronic oral THC

BACKGROUND

Determining time since last cannabis/Δ9-tetrahydrocannabinol (THC) exposure is important in clinical, workplace, and forensic settings. Mathematical models calculating time of last exposure from whole blood concentrations typically employ a theoretical 0.5 whole blood-to-plasma (WB/P) ratio. No studies previously evaluated predictive models utilizing empirically-derived WB/P ratios, or whole blood cannabinoid pharmacokinetics after subchronic THC dosing.

METHODS

Ten male chronic, daily cannabis smokers received escalating around-the-clock oral THC (40-120 mg daily) for 8 days. Cannabinoids were quantified in whole blood and plasma by two-dimensional gas chromatography-mass spectrometry.

RESULTS

Maximum whole blood THC occurred 3.0 h after the first oral THC dose and 103.5h (4.3 days) during multiple THC dosing. Median WB/P ratios were THC 0.63 (n=196), 11-hydroxy-THC 0.60 (n=189), and 11-nor-9-carboxy-THC (THCCOOH) 0.55 (n=200). Predictive models utilizing these WB/P ratios accurately estimated last cannabis exposure in 96% and 100% of specimens collected within 1-5h after a single oral THC dose and throughout multiple dosing, respectively. Models were only 60% and 12.5% accurate 12.5 and 22.5h after the last THC dose, respectively.

CONCLUSIONS

Predictive models estimating time since last cannabis intake from whole blood and plasma cannabinoid concentrations were inaccurate during abstinence, but highly accurate during active THC dosing. THC redistribution from large cannabinoid body stores and high circulating THCCOOH concentrations create different pharmacokinetic profiles than those in less than daily cannabis smokers that were used to derive the models. Thus, the models do not accurately predict time of last THC intake in individuals consuming THC daily.

Oral fluid and plasma cannabinoid ratios after around-the-clock controlled oral Δ(9)-tetrahydrocannabinol administration

BACKGROUND

Oral fluid (OF) testing is increasingly important for drug treatment, workplace, and drugged-driving programs. There is interest in predicting plasma or whole-blood concentrations from OF concentrations; however, the relationship between these matrices is incompletely characterized because of few controlled drug-administration studies.

METHODS

Ten male daily cannabis smokers received around-the-clock escalating 20-mg oral Δ(9)-tetrahydrocannabinol (THC, dronabinol) doses (40-120 mg/day) for 8 days. Plasma and OF samples were simultaneously collected before, during, and after dosing. OF THC, 11-hydroxy-THC and 11-nor-9-carboxy-THC (THCCOOH) were quantified by GC-MS at 0.5-μg/L, 0.5-μg/L, and 7.5-ng/L limits of quantification (LOQs), respectively. In plasma, the LOQs were 0.25 μg/L for THC and THCCOOH, and 0.5 μg/L for 11-hydroxy-THC.

RESULTS

Despite multiple oral THC administrations each day and increasing plasma THC concentrations, OF THC concentrations generally decreased over time, reflecting primarily previously self-administered smoked cannabis. The logarithms of the THC concentrations in oral fluid and plasma were not significantly correlated (r = -0.10; P = 0.065). The OF and plasma THCCOOH concentrations, albeit with 1000-fold higher concentrations in plasma, increased throughout dosing. The logarithms of OF and plasma THCCOOH concentrations were significantly correlated (r = 0.63; P < 0.001), although there was high interindividual variation. A high OF/plasma THC ratio and a high OF THC/THCCOOH ratio indicated recent cannabis smoking.

CONCLUSIONS

OF monitoring does not reliably detect oral dronabinol intake. The time courses of THC and THCCOOH concentrations in plasma and OF were different after repeated oral THC doses, and high interindividual variation was observed. For these reasons, OF cannabinoid concentrations cannot predict concurrent plasma concentrations.

Identification of recent cannabis use: whole-blood and plasma free and glucuronidated cannabinoid pharmacokinetics following controlled smoked cannabis administration

BACKGROUND

Δ⁹-Tetrahydrocannabinol (THC) is the most frequently observed illicit drug in investigations of accidents and driving under the influence of drugs. THC-glucuronide has been suggested as a marker of recent cannabis use, but there are no blood data following controlled THC administration to test this hypothesis. Furthermore, there are no studies directly examining whole-blood cannabinoid pharmacokinetics, although this matrix is often the only available specimen.

METHODS

Participants (9 men, 1 woman) resided on a closed research unit and smoked one 6.8% THC cannabis cigarette ad libitum. We quantified THC, 11-hydroxy-THC (11-OH-THC), 11-nor-9-carboxy-THC (THCCOOH), cannabidiol (CBD), cannabinol (CBN), THC-glucuronide and THCCOOH-glucuronide directly in whole blood and plasma by liquid chromatography/tandem mass spectrometry within 24 h of collection to obviate stability issues.

RESULTS

Median whole blood (plasma) observed maximum concentrations (C(max)) were 50 (76), 6.4 (10), 41 (67), 1.3 (2.0), 2.4 (3.6), 89 (190), and 0.7 (1.4) μg/L 0.25 h after starting smoking for THC, 11-OH- THC, THCCOOH, CBD, CBN, and THCCOOH-glucuronide, respectively, and 0.5 h for THC-glucuronide. At observed C(max), whole-blood (plasma) detection rates were 60% (80%), 80% (90%), and 50% (80%) for CBD, CBN, and THC-glucuronide, respectively. CBD and CBN were not detectable after 1 h in either matrix (LOQ 1.0 μg/L).

CONCLUSIONS

Human whole-blood cannabinoid data following cannabis smoking will assist whole blood and plasma cannabinoid interpretation, while furthering identification of recent cannabis intake.

Direct quantification of cannabinoids and cannabinoid glucuronides in whole blood by liquid chromatography-tandem mass spectrometry

The first method for quantifying cannabinoids and cannabinoid glucuronides in whole blood by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed and validated. Solid-phase extraction followed protein precipitation with acetonitrile. High-performance liquid chromatography separation was achieved in 16 min via gradient elution. Electrospray ionization was utilized for cannabinoid detection; both positive (Δ(9)-tetrahydrocannabinol [THC] and cannabinol [CBN]) and negative (11-hydroxy-THC [11-OH-THC], 11-nor-9-carboxy-THC [THCCOOH], cannabidiol [CBD], THC-glucuronide, and THCCOOH-glucuronide) polarity were employed with multiple reaction monitoring. Calibration by linear regression analysis utilized deuterium-labeled internal standards and a 1/x(2) weighting factor, yielding R(2) values >0.997 for all analytes. Linearity ranged from 0.5 to 50 μg/L (THC-glucuronide), 1.0-100 μg/L (THC, 11-OH-THC, THCCOOH, CBD, and CBN), and 5.0-250 μg/L (THCCOOH-glucuronide). Imprecision was <10.5% CV, recovery was >50.5%, and bias within ±13.1% of target for all analytes at three concentrations across the linear range. No carryover and endogenous or exogenous interferences were observed. This new analytical method should be useful for quantifying cannabinoids in whole blood and further investigating cannabinoid glucuronides as markers of recent cannabis intake.

Postmortem redistribution of Δ9-tetrahydrocannabinol (THC), 11-hydroxy-THC (11-OH-THC), and 11-nor-9-carboxy-THC (THCCOOH)

INTRODUCTION

Postmortem redistribution (PMR), a well-described phenomenon in forensic toxicology for certain drugs, can result in increased central blood concentrations relative to peripheral blood concentrations. Δ(9)-tetrahydrocannabinol (THC), the primary psychoactive component in cannabis or marijuana, is the illicit substance most commonly implicated in driving under the influence of drugs (DUID) cases and fatally-injured drivers. No investigation of PMR of THC in human blood has been reported to date.

METHODS

Matched heart and iliac postmortem blood specimens were collected from 19 medical examiner cases (16 Males, 3 Females) with positive cannabinoid urine immunoassay screens. THC, its equipotent metabolite 11-hydroxy-THC (11-OH-THC) and non-psychoactive metabolite 11-nor-9-carboxy-THC (THCCOOH) were quantified by two-dimensional gas chromatography-mass spectrometry with cryofocusing, with 0.5 ng/mL limits of quantification (LOQ) for all analytes.

RESULTS

10 cases had quantifiable THC and 11-OH-THC; THCCOOH was present in all 19. Median (range) heart:iliac blood ratios were 1.5 for THC (range: 0.3-3.1); 1.6 for 11-OH-THC (range: 0.3-2.7); and 1.8 for THCCOOH (range: 0.5-3.0).

DISCUSSION

Cannabinoids, in general, exhibited a mean and median central:peripheral (C:P) concentration ratio of less than 2 following death. A trend was observed for greater PMR with increasing postmortem interval between death and sampling. To our knowledge, these are the first data on THC PMR in humans, providing important scientific data to aid in the interpretation of postmortem cannabinoid concentrations in medico-legal investigations.

Forensic toxicology

Forensic toxicology has developed as a forensic science in recent years and is now widely used to assist in death investigations, in civil and criminal matters involving drug use, in drugs of abuse testing in correctional settings and custodial medicine, in road and workplace safety, in matters involving environmental pollution, as well as in sports doping. Drugs most commonly targeted include amphetamines, benzodiazepines, cannabis, cocaine and the opiates, but can be any other illicit substance or almost any over-the-counter or prescribed drug, as well as poisons available to the community. The discipline requires high level skills in analytical techniques with a solid knowledge of pharmacology and pharmacokinetics. Modern techniques rely heavily on immunoassay screening analyses and mass spectrometry (MS) for confirmatory analyses using either high-performance liquid chromatography or gas chromatography as the separation technique. Tandem MS has become more and more popular compared to single-stage MS. It is essential that analytical systems are fully validated and fit for the purpose and the assay batches are monitored with quality controls. External proficiency programs monitor both the assay and the personnel performing the work. For a laboratory to perform optimally, it is vital that the circumstances and context of the case are known and the laboratory understands the limitations of the analytical systems used, including drug stability. Drugs and poisons can change concentration postmortem due to poor or unequal quality of blood and other specimens, anaerobic metabolism and redistribution. The latter provides the largest handicap in the interpretation of postmortem results.

Conventional and alternative matrices for driving under the influence of cannabis: recent progress and remaining challenges

In the past decade much research concerning the impact of cannabis use on road safety has been conducted. More specifically, studies on effects of cannabis smoking on driving performance, as well as epidemiological studies and cannabis-detection techniques have been published. As a result, several countries have adopted driving under the influence of drugs (DUID) legislations, with varying approaches worldwide. A wide variety of bodily fluids have been utilized to determine the presence of cannabis. Urine and blood are the most widely used matrices for DUID legislations. However, more and more publications focus on the usability of oral fluid testing for this purpose. Each matrix provides different information about time and extent of use and likelihood of impairment. This review will focus on the practical aspects of implying a DUID legislation. The pros and cons of the different biological matrices used for Δ9-tetrahydrocannabinol screening and quantification will be discussed. In addition, a literature overview concerning (roadside) cannabinoid detection, as well as laboratory confirmation techniques is given. Finally, we will discuss important issues influencing interpretation of these data, such as oral fluid collection, choice of cut-offs, stability and proficiency testing.

Do Delta9-tetrahydrocannabinol concentrations indicate recent use in chronic cannabis users?

AIMS

To quantify blood Delta(9)-tetrahydrocannabinol (THC) concentrations in chronic cannabis users over 7 days of continuous monitored abstinence.

PARTICIPANTS

Twenty-five frequent, long-term cannabis users resided on a secure clinical research unit at the US National Institute on Drug Abuse under continuous medical surveillance to prevent cannabis self-administration.

MEASUREMENTS

Whole blood cannabinoid concentrations were determined by two-dimensional gas chromatography-mass spectrometry.

FINDINGS

Nine chronic users (36%) had no measurable THC during 7 days of cannabis abstinence; 16 had at least one positive THC > or =0.25 ng/ml, but not necessarily on the first day. On day 7, 6 full days after entering the unit, six participants still displayed detectable THC concentrations [mean +/- standard deviation (SD), 0.3 +/- 0.7 ng/ml] and all 25 had measurable carboxy-metabolite (6.2 +/- 8.8 ng/ml). The highest observed THC concentrations on admission (day 1) and day 7 were 7.0 and 3.0 ng/ml, respectively. Interestingly, five participants, all female, had THC-positive whole blood specimens over all 7 days. Body mass index did not correlate with time until the last THC-positive specimen (n = 16; r = -0.2; P = 0.445).

CONCLUSIONS

Substantial whole blood THC concentrations persist multiple days after drug discontinuation in heavy chronic cannabis users. It is currently unknown whether neurocognitive impairment occurs with low blood THC concentrations, and whether return to normal performance, as documented previously following extended cannabis abstinence, is accompanied by the removal of residual THC in brain. These findings also may impact on the implementation of per se limits in driving under the influence of drugs legislation.

Implications of plasma Delta9-tetrahydrocannabinol, 11-hydroxy-THC, and 11-nor-9-carboxy-THC concentrations in chronic cannabis smokers

Delta(9)-Tetrahydrocannabinol (THC) is commonly found in toxicological specimens from driving under the influence and accident investigations. Plasma cannabinoid concentrations were determined in 18 long-term heavy cannabis smokers residing on an in-patient research unit for seven days of monitored abstinence. THC, 11-hydroxy-THC, and 11-nor-9-carboxy-THC (THCCOOH) were quantified by two-dimensional gas chromatography-mass spectrometry with cryofocusing. THC concentrations were > 1 ng/mL in nine (50.0%) participants (1.2-5.5 ng/mL) on abstinence day 7. THCCOOH was detected (2.8-45.6 ng/mL) in all participants on study day 7. THC and THCCOOH median percent concentration decreases (n = 18) were 39.5% and 72.9% from day 1 to 7, respectively. Most (88.9%) of the participants had at least one specimen with increased THC compared to the previous day. Cannabis use duration and plasma THCCOOH concentrations were positively correlated on days 1-3 (R = 0.584-0.610; p = 0.007-0.011). There were no significant correlations between THC concentrations > 0.25 ng/mL and body mass index on days 1-7 (R = -0.234-0.092; p = 0.350-0.766). Measurable THC concentrations after seven days of abstinence indicate a potential mechanism for residual neurocognitive impairment observed in chronic cannabis users. THC's presence in plasma for seven days of abstinence suggests its detection may not indicate recent use in daily cannabis users.