The largest study of its kind has revealed the impact of THC on driving impairment, with potential implications for current drug laws.
A two-year randomised trial, conducted at the Center for Medicinal Cannabis Research (CMCR) at University of California San Diego School of Medicine, has found no relationship between blood THC concentrations and driving performance.
Researchers recruited almost 200 regular cannabis users to consume different levels of delta-9-tetrahydrocannabinol (THC), the intoxicating compound in cannabis, or a placebo, immediately before a series of driving simulation tests over several hours.
Eighteen states in the US have now legalised cannabis for recreational use, 13 have decriminalised its use and 36 have medical cannabis laws, provoking questions about how cannabis may affect the abilities of drivers under the influence.
Compared to participants who took the placebo, the THC group (who had smoked a cannabis cigarette with either 5.9 percent or 13.4 percent THC) displayed significantly diminished ability on a Composite Drive Score (CDS) that assessed key simulated driving variables, such as swerving in lane, responding to divided attention tasks and following a lead car.
However, not all individuals displayed significantly diminished driving skills compared to the placebo group, with researchers concluding that approximately 50 percent could be described as “impaired.”
The comparative decline was sharpest at the 30-minute and one hour-30 minute marks, after inhaling cannabis, then levelled to borderline differences with the placebo at three hours-30 minute mark.
There were no differences found at four hours-30 minutes.
The authors said driving scores did not differ based on THC content of the cigarette, both the 5.9 percent and 13.4 percent groups performed similarly.
The group with the highest use-intensity cannabis in the past six months attained significantly higher blood THC concentrations after smoking, but performed no worse than those with lower THC concentrations, indicating behavioural tolerance.
However, they appeared to compensate by ingesting more THC and performed no better than less frequent users.
The study found no relationship between post-smoking blood THC concentrations and simulator performance.
Co-author Robert Fitzgerald, PhD, professor of clinical pathology at UC San Diego School of Medicine and director of the Toxicology Laboratory and associate director of Clinical Chemistry Laboratory at UC San Diego Health said: “The complete lack of correlation between blood concentrations and driving performance was somewhat surprising. It’s strong evidence against developing ‘per se’ driving under the influence statutes.”
“These laws establish a statutory violation if a legal standard is breached, such as blood-alcohol concentration in driving under the influence laws.
The findings, say the authors, indicate that cannabis use resulted in diminished driving ability, but when experienced users controlled their intake, impairment could not be inferred based on THC content of the cigarette, behavioral tolerance or THC blood concentrations.
California State Assembly member Tom Lackey, commented: “This groundbreaking research indicates that cannabis use does impair driving ability, but factors differ from alcohol.
“For example, these data show that per se laws for THC levels are not supported scientifically. It also underscores the need for further research on this topic. Policymakers still need a better understanding of the effects of different ways of consuming higher concentration products to charter a path forward.”
The authors wrote that future research should address factors such as individual biologic differences, personal experience with cannabis and cannabis administration methods in relation to driving impairment.
These findings are in keeping with other research, published last year, which found that THC in blood and saliva are poor measures of cannabis impairment.
Researchers at the University of Sydney’s Lambert Initiative analysed all available studies on the relationship between driving performance and concentrations in blood and saliva of THC.
For infrequent, or occasional cannabis users, some significant correlations between blood and oral fluid THC concentrations and impairment were observed. However, the researchers note that most of these relationships were “weak” in strength.
No significant relationship between blood THC concentration and driving performance was observed for ‘regular’ (weekly or more often) cannabis users.
How THC and CBD work together in the brain – new study
New findings on how CBD and THC – the psychoactive compound in cannabis – affect the brain when administered together, could help to develop new cannabinoid therapeutics, scientists say.
A study has investigated the impact on the brain of CBD and THC, both as separate entities and when co-administered.
Researchers at University College London (UCL) analysed data from previous studies, including one which used functional Magnetic Resonance Imaging (fMRI) technology to measure brain activity in participants taking CBD and THC.
For the first time, they explored the response of the striatum region of the brain – a major part of the motor and reward systems. This is a critical component of numerous aspects of cognition, including motor and action planning, decision-making and motivation.
One study compared inhaled cannabis containing 8 mg THC, 8 mg THC + 10 mg CBD and a placebo. It showed strong disruptive effects of both THC and THC + CBD on connectivity in the associative and sensorimotor networks.
However it also identified a “specific effect of THC” in the limbic striatum network which was not present in the THC + CBD condition.
In a second study, testing oral 600 mg CBD versus placebo, CBD increased connectivity in the associative network, but produced only relatively minor disruptions in the limbic and sensorimotor networks.
The study concludes that THC “strongly disrupts striato-cortical networks” but that this effect is mitigated by the co-administration of CBD.
It states: “Oral CBD administered has a more complex effect profile of relative increases and decreases in connectivity.
“The insula [part of the brain implemented in diverse functions including emotions and self-awareness] emerges as a key region affected by cannabinoid-induced changes in functional connectivity, with potential implications for understanding cannabis-related disorders, and the development of cannabinoid therapeutics.”
This is the first report in human subjects of data from THC, THC + CBD and CBD use achieved “using a unified set of analysis methods, and with all comparisons performed in a placebo-controlled, double-blind design”.
Read the full report here.
Five new cannabis studies to have on your radar
The latest scientific papers exploring cannabis and its impact on health and society.
Get up to date with the latest cannabis-related research from across the globe.
Over the past few weeks, we’ve seen papers published around inaccurate labelling, the effects of cannabis on Covid-19, the impact of legalisation in Uruguay and how cannabis users might require more sedation during medical procedures.
Read on for five significant studies to dive into.
Lower Covid-19 severity among cannabis users
The researchers aimed to assess whether current cannabis users hospitalised for Covid-19 had different outcomes compared to non-users through a retrospective analysis of 1,831 patients admitted to UCLA Medical Centre in California.
Analysis of the data found that cannabis users had significantly better outcomes compared to non-users, shorter hospitalisation, lower ICU admission rates and less need for mechanical ventilation.
Interestingly, the researchers also found that active users had lower levels of inflammatory markers upon admission than non-users.
The authors of the study concluded: “This retrospective cohort study suggests that active marijuana users hospitalised with COVID-19 had better clinical outcomes compared with non-users. However, our results need to be interpreted with caution given the limitations of a retrospective analysis.
“Prospective and observational studies will better help elucidate the effects of marijuana use in COVID-19 patients.”
Cannabis users require more sedation for endoscopy
According to new research, patients who use cannabis required higher levels of sedation during gastric endoscopies than non-users.
As cannabis is legalised in more places and usage continues to rise, researchers in Canada said clinicians should be aware of patients’ cannabis consumption and prepare themselves for increased sedation and the risks that come with it.
The authors of the study conducted a prospective cohort study of 419 adult outpatients undergoing endoscopic procedures at three Canadian centres. Procedures were conducted under conscious sedation, which leaves the patient relaxed and comfortable but partially conscious during the procedure.
Cannabis use was associated with increased odds of requiring higher total sedation during gastroscopy, an endoscopic procedure that begins with the insertion of a tube and camera through the throat.
Legalisation not associated with increased cannabis use among young people
A recent study from researchers in Uruguay found that the use of cannabis following legalisation decreased among teenagers.
Uruguay was the first country in the world to legalise and regulate recreational cannabis. Since legalising the drug in 2016, the country is now regarded as a pioneer, paving the way for other countries like Canada, Mexico and Malta.
Using data from cross-sectional surveys of secondary students in Uruguay and Chile, the study evaluated changes in the prevalence of past-year, past-month and any risky and frequent cannabis use following the enactment and implementation of cannabis legalisation
“The legalisation of recreational cannabis in Uruguay was not associated with overall increases in either past-year/past-month cannabis use or with multi-year changes in any risky and frequent cannabis use among young people,” the authors stated in the paper’s abstract.
Current cannabis labelling system “doesn’t tell you much”
Labels like indica, sativa and hybrid—commonly used to distinguish one category of cannabis from another—tell consumers little about what’s in their product and could be confusing or misleading, suggests a new study of nearly 90,000 samples across six states in America.
Published on 19 May in the journal PLOS One, the research constitutes the largest analysis to date of the chemical composition of cannabis products.
It finds that commercial labels “do not consistently align with the observed chemical diversity” of the product. The authors are now calling for a “weed labelling system” akin to the Food and Drug Administration’s “nutrition facts panel” for food.
“Our findings suggest that the prevailing labelling system is not an effective or safe way to provide information about these products,” said co-author Brian Keegan, an assistant professor of Information Science at CU Boulder.
“This is a real challenge for an industry that is trying to professionalise itself.”
Cannabis dependence treatment is effective in tackling common co-morbidities
Earlier this month, Australian researchers released a paper looking into the effectiveness of cannabis dependency treatment on common co-morbidities, including mood, sleep and pain problems.
The researchers found that the treatment helped decrease anxiety, stress and sleep disturbance among the cohort of 128 cannabis-dependent participants.
The analysis used data from a 12-week double-blind placebo-controlled trial testing the effectiveness of the cannabis-based medicine nabiximols against placebo in reducing illicit cannabis use.
The researchers found that there was “no evidence” that nabiximols treatment is a barrier to reducing co-morbid symptoms. In fact, they found that the treatment reduced illicit cannabis use and improved comorbidity symptoms, even when participants were not able to achieve abstinence.
Research finds cannabis consumers may require more sedation
Consumers required higher levels of sedation during endoscopic procedures than non-users
Experts have highlighted the need for doctors to be more aware of their patients cannabis use, as research suggests consumers may require higher levels of sedation.
As cannabis is legalised in more places and usage continues to rise, researchers in Canada said clinicians should be aware of patients’ cannabis consumption, and prepare themselves for increased sedation and the risks that come with it.
It comes as a new study has associated cannabinoid use with increased odds of requiring higher total sedation during gastric endoscopies – a procedure that begins with the insertion of a tube and camera through the throat – than non-users.
The authors of the study conducted a prospective cohort study of 419 adult outpatients undergoing endoscopic procedures at three Canadian centres.
Procedures were conducted under conscious sedation, which leaves the patient relaxed and comfortable but partially conscious during the procedure.
“Patients didn’t have increased awareness or discomfort during procedures, but they did require more drugs,” said Yasmin Nasser, MD, PhD, lead researcher on the study and assistant professor at Snyder Institute for Chronic Diseases at the University of Calgary.
Each patient completed two questionnaires, one before the procedure about their cannabis use and another afterwards, indicating their awareness and comfort level during the procedure. The questionnaires were analysed along with details about the use of the sedatives midazolam, fentanyl and diphenhydramine during the procedure.
Cannabis use was associated with increased odds of requiring higher total sedation—defined as more than 5 mg of midazolam, or more than 100 mcg of fentanyl, or the need for diphenhydramine.
Interestingly, cannabis use was not associated with higher use of sedation during colonoscopy. Researchers said this could be because gastroscopy generally requires more sedation than colonoscopy due to the irritation caused in the upper part of the gastrointestinal tract.
Cannabinoid use was not independently associated with fentanyl use or adverse events, nor was it associated with intra-procedural awareness or discomfort, the authors found.
This study looked at whether patients were users or non-users of cannabis, but did not examine the timing, quantity or route of cannabis intake prior to the procedure. Researchers say these variables could be the basis for future studies.
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