Cannabis-induced Impairment Research Articles

How to read a paper on the short-term impairing effects of cannabis: A selective and critical review of the literature

The prosecution of cannabis-presence driving offences (in the absence of any behavioural evidence of impairment) is ultimately based on the assumption that there is a tight causal relationship between positive toxicology for cannabis and impairment. The main purpose of this review is to examine the evidence for that relationship. We show that most experimental studies have failed to elicit statistically-significant cannabis-induced impairments for many of their possible outcomes. And many studies failed to demonstrate any impairment at all in regular users of cannabis (because of the development of tolerance). We argue that selective reporting by researchers, editors and the media has created the false impression that the evidence for cannabis-induced impairment is strong and consistent. Human beings are ‘over-engineered’ for the psychomotor skills required to drive safely. A benchmark level of cannabis-induced impairment is therefore required to distinguish unproblematic from ‘real-world’ impairment. The conventional benchmarks of statistical significance, effect size and BAC-equivalence are shown to be inadequate. However, a benchmark in terms of 30 years of normal cognitive aging has good face validity. The recent use of cannabis is indicated toxicologically by the presence of delta-9-tetrahydrocannabinol (THC) in blood or oral fluid. Evidence is provided that most THC-positive drivers are not impaired, and certainly not meaningfully impaired. It follows that the justice of stand-alone cannabis-presence driving offences must be questioned.

Assessment of cognitive and psychomotor impairment, subjective effects, and blood THC concentrations following acute administration of oral and vaporized cannabis.

Cannabis legalization is expanding, but there are no established methods for detecting cannabis impairment. Characterize the acute impairing effects of oral and vaporized cannabis using various performance tests. Participants (N = 20, 10 men/10 women) who were infrequent cannabis users ingested cannabis brownies (0, 10, and 25 mg Δ-9-tetrahydrocannabinol, THC) and inhaled vaporized cannabis (0, 5, and 20 mg THC) in six double-blind outpatient sessions. Cognitive/psychomotor impairment was assessed with a battery of computerized tasks sensitive to cannabis effects, a novel test (the DRiving Under the Influence of Drugs, DRUID®), and field sobriety tests. Blood THC concentrations and subjective drug effects were evaluated. Low oral/vaporized doses did not impair cognitive/psychomotor performance relative to placebo but produced positive subjective effects. High oral/vaporized doses impaired cognitive/psychomotor performance and increased positive and negative subjective effects. The DRUID® was the most sensitive test to cannabis impairment, as it detected significant differences between placebo and active doses within both routes of administration. Women displayed more impairment on the DRUID® than men at the high vaporized dose only. Field sobriety tests showed little sensitivity to cannabis-induced impairment. Blood THC concentrations were far lower after cannabis ingestion versus inhalation. After inhalation, blood THC concentrations typically returned to baseline well before pharmacodynamic effects subsided. Standard approaches for identifying impairment due to cannabis exposure (i.e. blood THC and field sobriety tests) have severe limitations. There is a need to identify novel biomarkers of cannabis exposure and/or behavioral tests like the DRUID® that can reliably and accurately detect cannabis impairment at the roadside and in the workplace.

Cerebellar alterations in cannabis users: A systematic review.

Cannabis is the most used illicit substance in the world. As many countries are moving towards decriminalization, it is crucial to determine whether and how cannabis use affects human brain and behavior. The role of the cerebellum in cognition, emotion, learning, and addiction is increasingly recognized. Because of its high density in CB1 receptors, it is expected to be highly affected by cannabis use. The aim of this systematic review is to investigate how cannabis use affects cerebellar structure and function, as well as cerebellar-dependent behavioral tasks. Three databases were searched for peer-reviewed literature published until March 2018. We included studies that focused on cannabis effects on cerebellar structure, function, or cerebellar-dependent behavioral tasks. A total of 348 unique records were screened, and 40 studies were included in the qualitative synthesis. The most consistent findings include (1) increases in cerebellar gray matter volume after chronic cannabis use, (2) alteration of cerebellar resting state activity after acute or chronic use, and (3) deficits in memory, decision making, and associative learning. Age of onset and higher exposure to cannabis use were frequently associated with increased cannabis-induced alterations. Chronic cannabis use is associated with alterations in cerebellar structure and function, as well as with deficits in behavioral paradigms that involve the cerebellum (eg, eyeblink conditioning, memory, and decision making). Future studies should consider tobacco as confounding factor and use standardized methods for assessing cannabis use. Paradigms exploring the functional activity of the cerebellum may prove useful as monitoring tools of cannabis-induced impairment.

Women can force men to have sex? Forced sex tactic and substance use among sexually victimized men

Cannabis use can induce acute psychotic symptoms and increase the risk of schizophrenia. Impairments in inhibitory control and processing are known to occur both under the influence of cannabis and in schizophrenia. Whether cannabis-induced impairment in inhibitory processing is related to the acute induction of psychotic symptoms under its influence is unclear.We investigated the effects of acute oral administration of 10 mg of delta-9-tetrahydrocannabinol (delta-9-THC), the main psychoactive ingredient of cannabis, on inhibitory control and regional brain activation during inhibitory processing in humans and examined whether these effects are related to the induction of psychotic symptoms under its influence using a repeated-measures, placebo-controlled, double-blind, within-subject design. We studied thirty-six healthy, English-speaking, right-handed men with minimal previous exposure to cannabis and other illicit drugs twice using functional magnetic resonance imaging (fMRI) while they performed a response inhibition (Go/No-Go) task.Relative to placebo, delta-9-THC caused transient psychotic symptoms, anxiety, intoxication and sedation, inhibition errors and impaired inhibition efficiency. Severity of psychotic symptoms was directly correlated with inhibition error frequency and inversely with inhibition efficiency under the influence of delta-9-THC. Delta-9-THC attenuated left inferior frontal activation which was inversely correlated with the frequency of inhibition errors and severity of psychotic symptoms and positively with inhibition efficiency under its influence. These results provide experimental evidence that impairments in cognitive processes involved in the inhibitory control of thoughts and actions and inferior frontal function under the influence of cannabis may have a role in the emergence of transient psychotic symptoms under its influence.

Impairment of inhibitory control processing related to acute psychotomimetic effects of cannabis

Cannabis use can induce acute psychotic symptoms and increase the risk of schizophrenia. Impairments in inhibitory control and processing are known to occur both under the influence of cannabis and in schizophrenia. Whether cannabis-induced impairment in inhibitory processing is related to the acute induction of psychotic symptoms under its influence is unclear.We investigated the effects of acute oral administration of 10mg of delta-9-tetrahydrocannabinol (delta-9-THC), the main psychoactive ingredient of cannabis, on inhibitory control and regional brain activation during inhibitory processing in humans and examined whether these effects are related to the induction of psychotic symptoms under its influence using a repeated-measures, placebo-controlled, double-blind, within-subject design. We studied thirty-six healthy, English-speaking, right-handed men with minimal previous exposure to cannabis and other illicit drugs twice using functional magnetic resonance imaging (fMRI) while they performed a response inhibition (Go/No-Go) task.Relative to placebo, delta-9-THC caused transient psychotic symptoms, anxiety, intoxication and sedation, inhibition errors and impaired inhibition efficiency. Severity of psychotic symptoms was directly correlated with inhibition error frequency and inversely with inhibition efficiency under the influence of delta-9-THC. Delta-9-THC attenuated left inferior frontal activation which was inversely correlated with the frequency of inhibition errors and severity of psychotic symptoms and positively with inhibition efficiency under its influence. These results provide experimental evidence that impairments in cognitive processes involved in the inhibitory control of thoughts and actions and inferior frontal function under the influence of cannabis may have a role in the emergence of transient psychotic symptoms under its influence.

Cannabis Effects on Driving Skills

Cannabis is the most prevalent illicit drug identified in impaired drivers. The effects of cannabis on driving continue to be debated, making prosecution and legislation difficult. Historically, delays in sample collection, evaluating the inactive Δ(9)-tetrahydrocannabinol (THC) metabolite 11-nor-9-carboxy-THC, and polydrug use have complicated epidemiologic evaluations of driver impairment after cannabis use. We review and evaluate the current literature on cannabis' effects on driving, highlighting the epidemiologic and experimental data. Epidemiologic data show that the risk of involvement in a motor vehicle accident (MVA) increases approximately 2-fold after cannabis smoking. The adjusted risk of driver culpability also increases substantially, particularly with increased blood THC concentrations. Studies that have used urine as the biological matrix have not shown an association between cannabis and crash risk. Experimental data show that drivers attempt to compensate by driving more slowly after smoking cannabis, but control deteriorates with increasing task complexity. Cannabis smoking increases lane weaving and impaired cognitive function. Critical-tracking tests, reaction times, divided-attention tasks, and lane-position variability all show cannabis-induced impairment. Despite purported tolerance in frequent smokers, complex tasks still show impairment. Combining cannabis with alcohol enhances impairment, especially lane weaving. Differences in study designs frequently account for inconsistencies in results between studies. Participant-selection bias and confounding factors attenuate ostensible cannabis effects, but the association with MVA often retains significance. Evidence suggests recent smoking and/or blood THC concentrations 2-5 ng/mL are associated with substantial driving impairment, particularly in occasional smokers. Future cannabis-and-driving research should emphasize challenging tasks, such as divided attention, and include occasional and chronic daily cannabis smokers.

Reduced binocular depth inversion as an indicator of cannabis-induced censorship impairment

Measurements of binocular depth inversion using a stereoscopic slide projection with polarized light were performed in healthy volunteers before and after cannabis intake. Since binocular depth inversion represents an illusion occurring in the perception of semantically meaningful objects projected in a 3-D inverted fashion, the hypothesis can be tested that cannabis-induced “psychedelic states” represent a condition in which the human CNS is unable to correct implausible perceptual hypotheses. The data demonstrate a strong cannabis-induced impairment of binocular depth inversion.

Cannabis intoxication: effects of monetary incentive on performance, a controlled investigation of behavioural tolerance in moderate users of cannabis.

The study examined the effect of monetary incentive on the performance of five tasks after two heterogeneous groups of experienced users of cannabis and previously naive subjects had smoked placebo material and two dose levels of cannabis. The performance of the motivated subjects was compared with that of two non-motivated matched groups. Dose-related impairment was found on four of the five tasks, supporting previous findings of cannabis-induced impairment of short-term memory, goal-directed behavior and choice reaction times. Results for three of the tasks suggested that the performance of the motivated subjects was less affected by the drug than was the performance of the non-motivated subjects. There was no difference between the performance of subjects naive and experienced with respect to drug use.