Cannabis use in teens linked to risk of depression in young adults

Cannabis use among adolescents is found to be associated with increased risk of depression and anxiety in adulthood

February 13, 2019

Science Daily/University of Oxford

Cannabis is the most commonly used recreational drug by teenagers worldwide. In Canada, among youth aged 15 to 19 years, the rate of past-year cannabis use is 20.6 percent, while in England, 4 percent of adolescents aged 11 to 15 years used cannabis in the last month.

While there has been a lot of focus on the role of cannabis use in psychosis, there has been less attention on whether cannabis use is associated with an increased risk of common mental health disorders, such as depression and anxiety.

Researchers from McGill University and the University of Oxford carried out a systematic review and meta-analysis of the best existing evidence and analysed 23,317 individuals (from 11 international studies) to see whether use of cannabis in young people is associated with depression, anxiety and suicidality in early adulthood.

They found that cannabis use among adolescents is associated with a significant increased risk of depression and suicidality in adulthood (not anxiety). While the individual-level risk was found to be modest, the widespread use of the drug by young people makes the scale of the risk much more serious.

The population attributable risk was found to be around 7%, which translates to more than 400,000 adolescent cases of depression potentially attributable to cannabis exposure in the US, 25,000 in Canada and about 60,000 in the UK.

Dr. Gabriella Gobbi, Professor, Department of Psychiatry, McGill University and a scientist at the Research Institute of the McGill University Health Centre, states: "While the link between cannabis and mood regulation has been largely studied in preclinical studies, there was still a gap in clinical studies regarding the systematic evaluation of the link between adolescent cannabis consumption and the risk of depression and suicidal behaviour in young adulthood. This study aimed to fill this gap, helping mental health professionals and parents to better address this problem."

Professor Andrea Cipriani, NIHR Research Professor of Psychiatry at the University of Oxford, said: 'We looked at the effects of cannabis because its use among young people is so common, but the long-term effects are still poorly understood. We carefully selected the best studies carried out since 1993 and included only the methodologically sound ones to rule out important confounding factors, such us premorbid depression.'

'Our findings about depression and suicidality are very relevant for clinical practice and public health. Although the size of the negative effects of cannabis can vary between individual adolescents and it is not possible to predict the exact risk for each teenager, the widespread use of cannabis among the young generations makes it an important public health issue.

'Regular use during adolescence is associated with lower achievement at school, addiction, psychosis and neuropsychological decline, increased risk of motor vehicle crashes, as well as the respiratory problems that are associated with smoking.'

The active ingredient in cannabis,THC, mediates most of psychoactive and mood-related effects of cannabis and also has addictive properties. Preclinical studies in laboratory animals reported an association between pubertal exposure to cannabinoids and adult-onset depressive symptoms. It is thought that cannabis may alter the physiological neurodevelopment (frontal cortex and limbic system) of adolescent brains.

While the review of observational studies was the first to look at the effects of cannabis use in adolescents only, it was not possible to predict the risk at the individual level, nor was it possible to discern information about the dose-dependent risk of cannabis use.

https://www.sciencedaily.com/releases/2019/02/190213172307.htm

Parenting in the age of legal pot: Household rules, conversations help guide teen use

February 7, 2019

Science Daily/University of Washington

The legalization of marijuana in Washington state in 2012 gave parents the opportunity for a new teachable moment. Many say that as society has become more permissive, they want information and advic

When Washington voters legalized marijuana in 2012, many parents found themselves with a new teachable moment.

Though illegal for anyone under 21, the drug presented a dilemma similar to alcohol: Retailers sold it, people openly consumed it -- sometimes to excess -- and parents themselves struggled with how to talk to their kids about their own use, past or present.

Unlike with alcohol, research on the health and developmental effects of marijuana is still emerging. And the law's complexity, along with the accessibility of marijuana products and stores, has left parents thinking more deliberately about how and why to set some ground rules.

Most parents agree that marijuana should be off-limits to children and teenagers, but they want information and advice from trustworthy sources, said Nicole Eisenberg, a research scientist with the University of Washington's Social Development Research Group. Those findings come from a study published online Jan. 16 in the Journal of Child and Family Studies, by Eisenberg and a team of researchers.

"What I heard a lot of parents saying is, essentially, 'I can tell my kids not to use it, but I just don't know how to enforce and reinforce that message,'" Eisenberg said. "Parents are having a hard time reconciling societal norms with personal norms. Society has become more permissive, but at home, most parents don't want their children to use marijuana. It's a challenge that leaves them feeling like they don't know what to do."

To that end, parents said they want guidance, she added.

"Parents are eager to learn, and open to materials and programs that can help them. They're open to factual, unbiased, scientific information, and they want to know how to talk to their kids," Eisenberg said.

Based on focus group interviews with 54 adults, the study examined parents' attitudes and challenges around marijuana use. Researchers grouped parents according to the ages of their children and by their own usage of marijuana during the past year (as measured by a prior confidential survey); those who had used during the past year, to any degree, were in one group, and those who had not were in another. That separation was designed to better identify differences in how these groups parent; participants were not told anything about other group members' marijuana use.

Yet, in both groups, there were common themes that emerged which can be useful in delivering educational and prevention-oriented messages, Eisenberg said.

For parents, talking to kids about marijuana can mean many things: explaining its risks and effects, deciding on rules and consequences, and choosing whether to share their own history. Researchers didn't offer answers -- that wasn't their role, or the purpose of the study -- but parents appeared to appreciate hearing from each other, Eisenberg said.

Among the challenges parents discussed were adequate and appropriate consequences for breaking house rules, while a few parents of older kids, especially in the user-groups, described a harm-reduction approach, such as discussing with their teens how to use marijuana safely. Parents who chose this strategy said that while they didn't want their children to use marijuana, they figured that if the children were going to try it anyway, they might as well educate them.

What makes the issue so thorny is the relatively rapid legal and cultural change around marijuana, said Rick Kosterman, a co-author of the study from the Social Development Research Group. While marijuana has become even more available since these interviews were conducted in 2014, parents' questions are unlikely to have changed.

"In many ways, parenting around marijuana use is similar to that of alcohol use, since they're both legal for adults," Kosterman said. "A key difference is where I think parents and society in general have accepted that some people can become dependent on alcohol and it can ruin people's lives if used in excess. Parents and kids aren't so clear about risks of marijuana use -- like the potential for misuse or effects on adolescent brains.

"We are still learning about the risks of teen marijuana use, as well as potential medical uses."

The study's conclusion points to how parents might seek answers, whether through community-oriented drug prevention programs or through information from health care providers, public health agencies or school programs.

"The fact that parents in this study openly asked for guidance highlights an opportunity for the prevention science community to work with medical professionals, schools and policymakers to fulfill this vital need at a critical time of policy transition in the United States," the authors wrote.

Alongside this study of parenting practices is a companion study by the same research team, forthcoming in the Journal of the Society for Social Work and Research, about parent perceptions of teens' exposure to marijuana use following legalization in Washington state.

The parents who agreed to participate in both studies came from a longitudinal study the research group launched in the 1980s called the Seattle Social Development Project. The focus group sample was 39 percent white, 37 percent African American, 17 percent Asian American and 7 percent Native American. Of these groups, approximately 5 percent were Latino.

The study on parenting practices was funded by the National Institute on Drug Abuse. Additional authors were Tiffany Jones, a postdoctoral researcher at the UW School of Social Work and an affiliate at Colorado State University; Jennifer Bailey and Kevin Haggerty, of the Social Development Research Group; and Jungeun Olivia Lee of USC.

https://www.sciencedaily.com/releases/2019/02/190207123242.htm

Teen brain volume changes with small amount of cannabis use

January 14, 2019

Science Daily/Larner College of Medicine at the University of Vermont

At a time when several states are moving to legalize recreational use of marijuana, new research shows that concerns about the drug's impact on teens may be warranted. The study, published in The Journal of Neuroscience, shows that even a small amount of cannabis use by teenagers is linked to differences in their brains.

Senior author and University of Vermont (UVM) Professor of Psychiatry Hugh Garavan, Ph.D., and first author and former UVM postdoctoral fellow Catherine Orr, Ph.D., say this research is the first to find evidence that an increase in gray matter volume in certain parts of the adolescent brain is a likely consequence of low-level marijuana use.

Few studies have looked at the effects of the first few uses of a drug, says Garavan. Most researchers focus on heavy marijuana users later in life and compare them against non-users. These new findings identify an important new area of focus.

"Consuming just one or two joints seems to change gray matter volumes in these young adolescents," Garavan says.

The new study, part of a long-term European project known as IMAGEN, included 46 kids who reported having used cannabis once or twice by age 14. Their brains showed more gray matter volume in areas where cannabis binds, known as cannabinoid receptors, compared to the kids who didn't use the drug. The biggest differences in gray matter were in the amygdala, which is involved in fear and other emotion-related processes, and in the hippocampus, involved in memory development and spatial abilities.

Exploiting the advantages of the study's longitudinal data, the researchers ruled out the likelihood that the cannabis-using kids had pre-existing differences in gray matter thickness or that they had specific personality traits that might correlate with the difference in brain makeup.

"The implication is that this is potentially a consequence of cannabis use," Garavan says. "You're changing your brain with just one or two joints. Most people would likely assume that one or two joints would have no impact on the brain."

What the increased brain matter volume means is unclear.

Typically at that age, Garavan says, the adolescent brain undergoes a "pruning" process, where it gets thinner, rather than thicker as it refines its synaptic connections.

"One possibility is they've actually disrupted that pruning process," Garavan says of the marijuana-using kids.

https://www.sciencedaily.com/releases/2019/01/190114130855.htm

Exposure to cannabis and stress in adolescence can lead to anxiety disorders in adulthood

January 8, 2019

Science Daily/Universitat Pompeu Fabra - Barcelona

A new study conducted on laboratory animals shows that exposure to cannabis and stress during adolescence may lead to long-term anxiety disorders characterized by the presence of pathological fear. The work carried out by the Neuropharmacology Laboratory-NeuroPhar at Pompeu Fabra University, was led by the researchers Fernando Berrendero, now at Francisco de Vitoria University, and Rafael Maldonado, and has been published in the journal Neuropharmacology.

Cannabis remains the most commonly consumed illegal drug worldwide. Its regular use often begins during adolescence, which is especially troubling because this period is crucial for the brain to mature properly through the reorganization of the neuronal synapses.

Numerous preclinical and epidemiological data suggest that exposure to cannabinoids in adolescents may increase the risk of the onset of psychiatric illnesses in adulthood. The results of the National Drugs Plan show an increase in the consumption of cannabis and a recent review highlights that in recent years the perception of the risk of its consumption has diminished among the young population, from 12 to 17 years of age, the age group discussed in this article.

"In this study we have investigated the effects of simultaneous exposure to Δ9-tetrahydrocannabinol (THC), which is primarily responsible for the psychoactive properties of cannabis, and to stress during adolescence," explain Rocio Saravia and Marc Ten-Blanco, first authors of the article. Specifically, they have studied how this exposure during adolescence affects the extinction of the memory of fear in adult mice.

Occasionally, a stimulus that should be neutral, as could be, for example, seeing the dentist in a white coat, is associated with a threatening one, which would be the pain we have felt upon previous visits to the dentist, and causes a fear response. Normally, fear reactions diminish over time as the conditioned stimulus ceases to be associated with the negative experience. This is known as fear extinction. But when fear extinction does not occur properly, anxiety disorders such as post-traumatic stress syndrome, phobias or panic attacks occur.

"We have observed that adolescent mice treated with THC and exposed to stress display impaired fear extinction in adulthood. However, this effect was not observed in animals exposed to these same two factors separately," Fernando Berrendero explains. In addition, the resistance to fear extinction was associated with a decrease in neuronal activity in the basolateral amygdala and the infralimbic prefrontal cortex, suggesting a deregulation in the long term of the circuit that regulates fear.

"Our findings highlight the influence of environmental factors such as stress on the harmful effects of the exposure to cannabis during early ages and suggest that the consequences of early cannabis use greatly depend on the environment of its use," explains Rafael Maldonado, full professor of Pharmacology at UPF. "The presence of stress situations, common among consumers of the substance, may worsen the harmful effects of cannabis," he concludes.

Their study has also involved the researchers Humberto Gagliano, Antonio Armario and Raül Andero, of the Autonomous University of Barcelona. The article is part of a project funded by the Spanish National Drugs Plan.

https://www.sciencedaily.com/releases/2019/01/190108125419.htm

Cannabis-based compound may reduce seizures in children with epilepsy

December 5, 2018

Science Daily/Wiley

A recent analysis of published studies indicates that the use of cannabinoids for the treatment of epilepsy in children looks promising.

Interest has been growing in the use of cannabinoids -- the active chemicals in cannabis or marijuana -- for the treatment of epilepsy in children. A recent Epilepsia analysis of relevant published studies indicates that this strategy looks promising.

The analysis included four randomized controlled trials and 19 non-randomized studies, primarily involving cannabidiol, a particular type of cannabinoid that does not have psychoactive effects.

Among randomized controlled trials involving children with severe forms of epilepsy, there was no statistically significant difference between cannabidiol and placebo in terms of freedom from seizures, sleep disruption, or vomiting. There was a statistically significant reduction in the median frequency of monthly seizures with cannabidiol compared with placebo and an increase in number of participants with at least a 50 percent reduction in seizures.

"Although we saw no significant difference in the number of children who became completely seizure free, we that found a significant number of these children achieved a 50 percent or more reduction in seizures. Any reduction in seizures has a striking impact on the lives of these children and their families," said lead author Jesse Elliott, of the University of Ottawa, in Canada. "Research in this area is active, and we expect a dramatic increase in the number of studies over the next few years."

https://www.sciencedaily.com/releases/2018/12/181205093644.htm

Does teen cannabis use lead to behavior problems -- or vice versa?

November 26, 2018

Science Daily/Annenberg Public Policy Center of the University of Pennsylvania

New research finds that cannabis use among teens doesn't appear to lead to greater conduct problems or greater affiliation with other teens who smoke cannabis. Instead, it's adolescents with conduct problems or whose friends use cannabis who are more likely to gravitate toward cannabis use.

More youth use cannabis than smoke cigarettes in the United States. In other parts of the world, cannabis use has become almost as regular as tobacco use among adolescents and young adults.

With relaxed laws governing cannabis use in many U.S. states and localities, there is mixed and limited research on whether increasing legalization could lead to other unhealthy behaviors in addition to substance use disorders.

Now, new research led by the Annenberg Public Policy Center of the University of Pennsylvania finds that cannabis use among teens does not appear to lead to greater conduct problems or greater affiliation with other teens who smoke cannabis, associations that previous research had suggested to be possible.

Instead, it's the other way around: It is adolescents with conduct problems or whose friends use cannabis who are more likely to gravitate toward cannabis use. And that "cascading chain of events" appears to predict cannabis use disorder as the teens become young adults, according to the study, newly published in the journal Addiction.

"Cannabis use in and of itself does not appear to lead to conduct problems or increasing attraction to peers who use cannabis," said coauthor Dan Romer, research director of the Annenberg Public Policy Center (APPC).

The study follows a group of Philadelphia adolescents over eight years. "Previous studies have not been as able to isolate the effects of cannabis use in adolescents," Romer added. "But because we had measurements over the entire period of adolescence, we were able to disentangle the effects of cannabis use itself from other influences."

The Philadelphia Trajectory Study

The research uses data from the Philadelphia Trajectory Study, a six-wave study that began in 2004 with interviews of nearly 400 10- to 12-year-olds in Philadelphia. The adolescents were tested annually from 2004 to 2010, and then again in 2012 for a final two-year follow-up. The current study uses data from 364 teens from the final four waves of the study. The observational study is based on self-reports from the adolescents which were then validated by urine screening.

Ivy Defoe, the lead author and former APPC postdoctoral fellow, said, "Interestingly, the results show that not only do conduct problems such as school truancy and theft predict cannabis use, but adolescents who display conduct problems are also drawn to cannabis-using peers. These affiliations predict increases in cannabis use and, eventually, cannabis use disorder, as our results show," added Defoe, now a postdoctoral researcher at the University of Twente, the Netherlands.

Defoe said some theories would suggest that teens with conduct problems may be using cannabis as a coping mechanism to deal with disapproval of their behavior problems and perhaps to self-medicate. The study concludes that if youth with conduct problems "use unprescribed cannabis to cope with their condition, then healthier alternative coping strategies and support should be made available."

Concerns about cannabis

One concern about use of an illegal drug is that it will lead adolescents to socialize with deviant peer groups, such as those who sell and use illegal drugs. However, the study suggests that adolescents using cannabis are no more likely to start affiliating with peers using cannabis.

The findings do suggest that with increasing legalization, there will be greater access to cannabis and thus a greater likelihood for youth to develop cannabis use disorder. However, just as with alcohol, which is legal for adults, research conducted as part of this project suggests that less than a quarter of youthful users would develop a mild cannabis use disorder.

"Disentangling longitudinal relations between youth cannabis use, peer cannabis use, and conduct problems: developmental cascading links to cannabis use disorder" is published open access in the journal Addiction.

In addition to Defoe and Romer, the coauthors are Atika Khurana, Ph.D., an APPC distinguished research fellow at the University of Oregon, and Laura M. Betancourt, Ph.D., and Hallam Hurt, M.D., of the Children's Hospital of Philadelphia.

The research was supported by grants from the National Institute on Drug Abuse. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

The Annenberg Public Policy Center was established in 1993 to educate the public and policy makers about the media's role in advancing public understanding of political, health, and science issues at the local, state and federal levels.

https://www.sciencedaily.com/releases/2018/11/181126134248.htm

Compound derived from marijuana may benefit children with epilepsy

November 7, 2018

Science Daily/Wiley

In recent years, cannabinoids -- the active chemicals in medical marijuana -- have been increasingly touted as a potential treatment for a range of neurological and psychiatric disorders. In a Developmental Medicine & Child Neurology review, investigators compare their efficacy with antiepileptic drugs for children with epilepsy.

One cannabinoid, called cannabidiol (CBD), has the most evidence of antiepileptic efficacy and does not have psychoactive effects. There has been little evidence for its use apart from anecdotal reports, until the last year.

The review notes that in three randomized, placebo-controlled, double-blind trials in Dravet syndrome and Lennox-Gastaut syndrome (two forms of childhood epilepsy), CBD produced a 38 percent to 41 percent median reduction in all seizures compared with 13 percent to 19 percent with placebo. Similarly, CBD resulted in a 39 percent to 46 percent responder rate (50 percent convulsive or drop-seizure reduction) compared with 14 percent to 27 percent with placebo. CBD was well tolerated, however sedation, diarrhea, and decreased appetite were frequent.

"Community debate about the use of CBD and access to this antiepileptic therapy has been heated," the authors wrote. "With further trials and greater understanding of its role, the place of CBD in our antiepileptic armamentarium and its impact on comorbidities will become clearer."

https://www.sciencedaily.com/releases/2018/11/181107082534.htm

New insights into the neural risks and benefits of marijuana use

Compounds in cannabis can impair or improve memory depending on age, disease

November 6, 2018

Science Daily/Society for Neuroscience

Research released today underscores both the dangers and the therapeutic promise of marijuana, revealing different effects across the lifespan. Marijuana exposure in the womb or during adolescence may disrupt learning and memory, damage communication between brain regions, and disturb levels of key neurotransmitters and metabolites in the brain. In Alzheimer's disease, however, compounds found in marijuana, such as the psychoactive compound delta-9-tetrahydrocannabinol (THC), may improve memory and mitigate some of the disease's symptoms.

Research released today underscores both the dangers and the therapeutic promise of marijuana, revealing different effects across the lifespan. Marijuana exposure in the womb or during adolescence may disrupt learning and memory, damage communication between brain regions, and disturb levels of key neurotransmitters and metabolites in the brain. In Alzheimer's disease, however, compounds found in marijuana, such as the psychoactive compound delta-9-tetrahydrocannabinol (THC), may improve memory and mitigate some of the disease's symptoms. The findings were presented at Neuroscience 2018, the annual meeting of the Society for Neuroscience and the world's largest source of emerging news about brain science and health.

Marijuana is the most commonly used illicit drug in the United States and its popularity is expected to rise as it is legalized in more places. It is also the illegal drug most commonly used by pregnant women, despite the potential for long-term harm to the fetus. Many people start using marijuana as teenagers -- a particularly vulnerable time as the brain is still developing -- when there is evidence for increased risk. At the same time, a growing number of people are turning to marijuana for the relief of symptoms of chronic diseases such as epilepsy and multiple sclerosis. These use patterns highlight the need to better understand the long-term effects of marijuana, particularly in sensitive populations such as unborn children and adolescents.

Today's new findings show that:

·     Prenatal exposure to THC in rats has lasting effects on metabolites in the brain, making the animal more vulnerable to stress later in life (Robert Schwarcz, abstract 609.12).

·     Rats exposed to synthetic compounds that are similar to THC during fetal development show impaired formation of the neural circuits involved in learning and memory as adolescents (Priyanka Das Pinky, abstract 424.17).

·     Cannabinoid use by adolescent rats boosts activity in brain pathways responsible for habit formation (José Fuentealba Evans, abstract 602.07).

·     In adolescent rats, cannabinoids may disturb the development of a protein lattice important for balancing excitatory and inhibitory activity in a brain region involved in decision-making, planning, and self-control (Eliza Jacobs-Brichford, abstract 645.09).

·     Long-term cannabinoid use alters metabolism and connectivity of brain regions involved in learning and memory in adult mice (Ana M. Sebastião, abstract 778.08).

·     Treating Alzheimer's disease mice with the psychoactive compound found in marijuana improves memory and reduces neuronal loss, suggesting a possible therapy for the human disease (Yvonne Bouter, abstract 467.14).

"Today's findings lend new understanding of the complex effects that cannabis has on the brain," said press conference moderator Michael Taffe, PhD, of Scripps Research Institute and an expert in substance abuse research. "While it may have therapeutic potential in some situations, it is important to get a better understanding of the negative aspects as well, particularly for pregnant women, teens, and chronic users."

https://www.sciencedaily.com/releases/2018/11/181106150418.htm

Adolescent cannabis use alters development of planning, self-control brain areas

November 6, 2018

Science Daily/University of Illinois at Chicago

Adolescent marijuana use may alter how neurons function in brain areas engaged in decision-making, planning and self-control, according to researchers at the University of Illinois at Chicago.

The findings, which were presented at Neuroscience 2018, the annual meeting of the Society for Neuroscience, are the result of an animal model study focused on the structural development of the prefrontal cortex, or PFC, which controls high-level cognitive functions.

Within the PFC, a support structure called the perineuronal net forms a lattice of proteins around inhibitory cells, helping to secure their connections with excitatory neurons and regulate PFC activity. Perineuronal net formation is sensitive to drug use, but the effects of marijuana are not known.

To investigate how adolescent marijuana use affects perineuronal nets in the PFC, the UIC researchers gave adolescent rats a synthetic cannabinoid which was similar to THC, the main psychoactive compound in marijuana, for one day, 10 days, or 10 days followed by a period of abstinence. They then compared perineuronal net structure in these rats to those in drug-free animals.

Animals exposed to the cannabinoid showed a reduction in net development around inhibitory cells during adolescence, and this reduction was more common in male animals.

"Our evidence suggests that exposure to cannabinoids during adolescence alters brain maturation in the prefrontal cortex," said Eliza Jacobs-Brichford, study lead author and UIC Ph.D. candidate in psychology. "These results may offer a mechanistic explanation for functional and behavioral changes caused by adolescent cannabinoid exposure."

Recreational use of marijuana is among the risky choices often made by adolescents, and likely to become more prevalent with greater availability due to its shifting legal status in some states and Canada.

These impulsive choices are taking place during a key period of brain development and could have costs later in life, according to the researchers.

"Adolescence is a crucial time for fine-tuning the balance of excitatory and inhibitory neurons in the brain, which combine to control precise patterns of brain activity," said Jamie Roitman, UIC associate professor of psychology and study co-author. "Substance use as a teenager thus has the potential to disrupt the normal developmental trajectory of the PFC, with potentially long-term consequences for decision-making."

Hu Chen, UIC research assistant professor of psychiatry, and Amy Lasek, UIC associate professor of psychiatry, are co-authors on the paper.

The study was supported with funds from the National Institute on Drug Abuse, one of the National Institutes of Health, and a UIC Provost Award for Graduate Research.

https://www.sciencedaily.com/releases/2018/11/181106150439.htm

One month of abstinence from cannabis improves memory in adolescents, young adults

October 30, 2018

Science Daily/Massachusetts General Hospital

A Massachusetts General Hospital (MGH) study finds that one month of abstaining from cannabis use resulted in measurable improvement in memory functions important for learning among adolescents and young adults who are regular cannabis users. The study published in the Journal of Clinical Psychiatry is one of the first to prospectively track over time changes in cognitive function associated with halting cannabis use.

"Our findings provide two pieces of convincing evidence," says Randi Schuster, PhD, director of Neuropsychology at the Center for Addiction Medicine in the MGH Department of Psychiatry, lead author of the paper. "The first is that adolescents learn better when they are not using cannabis. The second -- which is the good news part of the story -- is that at least some of the deficits associated with cannabis use are not permanent and actually improve pretty quickly after cannabis use stops."

The authors note that the use of cannabis among adolescents is common, with more than 13 percent of middle and high school students reporting cannabis use in a recent survey and rates of daily use increasing between grades 8 and 12. But adolescence is a critical time for brain maturation, specifically for brain regions that are most susceptible to the effects of cannabis. A 2016 study from the same research team found that cannabis users aged 16 and under had difficulty learning new information, a problem that was not observed in users age 17 and older.

The current study is the first one able to determine not only whether cognitive improvement occurs but also when during abstinence this improvement is detectable. The study enrolled 88 participants ages 16 to 25 from the Boston area, all of whom acknowledged using cannabis at least once a week. Investigators compared weekly cognitive performance between a group of young cannabis users who agreed to stop their use for 30 days and a group that continued to use cannabis. To ensure that the two groups were as comparable as possible, they were randomized in a way that controlled for factors such as pre-existing differences in learning, mood, cognition and motivation, and the frequency and intensity of cannabis use.

Participants completed regular assessments of their thinking and memory during the study period. They also provided frequent urine tests to verify cannabis abstinence in those randomized to stop cannabis use and cannabis exposure in the continuing-use group. Members of both groups received incentive payments for study visits and among the abstinence group for adhering to cannabis abstinence.

Throughout the study period, the levels of the urinary cannabis biomarker steadily decreased among the abstinence group, with almost 89 percent meeting criteria for 30 days of continuous abstinence. In the continuing-use group, biomarker levels remained unchanged. Cognitive testing found memory -- specifically the ability to learn and recall new information -- improved only among those who stopped using cannabis, and this improvement occurred largely during the first week of abstinence. A month of cannabis abstinence was not associated with improvements in attention, and no aspect of cognitive functioning improved among those who continued cannabis use.

"The ability to learn or 'map down' new information, which is a critical facet of success in the classroom, improved with sustained non-use of cannabis." Schuster says. "Young cannabis users who stop regular -- weekly or more -- use may be better equipped to learn efficiently and therefore better positioned for academic success. We can confidently say that these findings strongly suggest that abstaining from cannabis helps young people learn, while continuing cannabis use may interfere with the learning process."

An assistant professor of Psychiatry at Harvard Medical School (HMS), Schuster adds, "There are still a lot of open questions to be studied, including whether attention might improve and memory continues to improve with longer periods of cannabis abstinence." Those questions and others are being addressed in a larger follow-up trial that includes younger participants -- ages 13 to 19 -- and a group that never used cannabis to help determine whether the cognitive improvements produced by cannabis abstinence return participants to performance levels similar to those of non-users. Another trial about to begin will follow young cannabis users who abstain for six months, investigating whether cognition continues to improve beyond 30 days and if those improvements can affect school performance.

https://www.sciencedaily.com/releases/2018/10/181030134333.htm