A quarter of problematic pot users have anxiety disorders, many since childhood

Regional data also suggest some teens who abuse pot outgrow habit in adulthood

October 24, 2017

Science Daily/Duke University Medical Center

About a quarter of adults whose marijuana use is problematic in early adulthood have anxiety disorders in childhood and late adolescence, according to new data from Duke Health researchers.

The findings, publishing this week in the November issue of the Journal of the American Academy of Child and Adolescent Psychiatry, also shed light on an estimated 4 percent of adults who endured childhood maltreatment and peer bullying without resorting to chronic marijuana abuse, only to develop problems with the drug between the ages of 26 and 30.

"Given that more states may be moving towards legalization of cannabis for medicinal and recreational purposes, this study raises attention about what we anticipate will be the fastest growing demographic of users -- adults," said lead author Sherika Hill, Ph.D., an adjunct faculty associate at the Duke University School of Medicine. "A lot of current interventions and policies in the U.S. are aimed at early adolescent users. We have to start thinking about how we are going to address problematic use that may arise in a growing population of older users."

The findings are based on data from 1,229 participants in the Great Smoky Mountains Study, a long-term study of residents in 11 counties near the Appalachian Mountains in western North Carolina, where Hispanics and Latinos are underrepresented and Native Americans are overrepresented compared to the rest of the U.S.

A cohort of children in the study were enrolled as young as age 9 and have now reached their 30s. From 1993 to 2015, researchers tracked data in numerous areas of interest, including mental health, education, work attainment, and use of drugs and alcohol.

The researchers defined problematic cannabis or marijuana use as daily consumption or a habit that meets diagnostic guidelines for addiction. They tracked participants' patterns of use from the college years (ages 19-21) into adulthood (ages 26-30).

They found more than three-fourths (76.3 percent) of participants didn't use or develop a problem with marijuana during this period.

The remaining quarter developed problems that researchers grouped into three profiles -- those with limited problems, persistent problems and delayed problems.

Limited users (13 percent)

·     Limited problematic users had trouble with marijuana either while in school before age 16 or in their late teens and early 20s, but their habits dropped off as they aged.

·     Researchers were somewhat surprised that this group reported the highest levels of family conflict and instability during childhood as compared to others in the study; these factors are often associated with more drug use.

·     "When this group of children left home, they seemed to do better," Hill said. "They didn't have as many children at a young age, and they went further in their education when they were 19 to 21 compared to those with persistent and delayed profiles."

Persistent users (7 percent)

·     This group had trouble with marijuana beginning as young as 9 years old and their chronic use continued into their late 20s and early 30s, the data showed.

·     Large portions of this group had anxiety disorders in both childhood (27 percent) and at ages 19-21 (23 percent).

·     They had the highest rates of psychiatric disorders and involvement in the criminal justice system, and most said the majority of their friends were drug users, too.

·     "This suggests that a focus on mental health and well-being could go a long way to prevent the most problematic use," Hill said.

Delayed users (4 percent)

·     This was a small but unique group that made it through adolescence and early adulthood without problematic marijuana use, only to become habitual users between ages 26 and 30.

·     Blacks were five times as likely as whites to be delayed problematic users in the late 20s and early 30s after not having trouble with the between the ages 19-21 -- a peak time for most marijuana users.

·     More than half of delayed users were both bullied by peers and mistreated by caregivers as children, yet also had lower rates of anxiety, alcohol use, and other hard drug use compared to persistent users.

·     "What we don't yet understand is how childhood maltreatment didn't prompt earlier problematic use of cannabis between ages 19 and 21 -- how individuals could be resilient to that kind of adverse experience for so long," Hill said. "One theory is that they were somewhat protected by having fewer peers in late adolescence who were substance users, but this is one of the questions we will continue to seek answers for."

https://www.sciencedaily.com/releases/2017/10/171024141720.htm

Limited data on medical cannabis use in children

Strongest evidence supports use to reduce seizures, side effects of chemotherapy

October 23, 2017

Science Daily/Massachusetts General Hospital

A systematic review of published studies on the use of medical cannabis in children and adolescents finds a notable lack of studies and a minimal number of the randomized, controlled trials needed to confirm the effectiveness of a treatment. In their paper published in the journal Pediatrics, Massachusetts General Hospital (MGH) investigators Shane Shucheng Wong, MD, and Timothy Wilens, MD -- both of the MGH Department of Psychiatry -- report that their review suggests only two pediatric uses of medical cannabis -- to relieve chemotherapy-induced nausea and vomiting and to reduce seizures -- are supported by existing studies.

"Medical cannabis is now legal in 29 states and the District of Columbia, and in those areas with active programs, children and adolescents can legally access medical cannabis with certification from their doctor and consent from a parent or guardian," says lead author Wong. "This means that doctors and families need to understand what we know and what we don't yet know about medical cannabis in order to make the best decision for the health of the individual child."

Two synthetic cannabinoids -- compounds that act on specific receptors in the brain -- have been approved for medical use in the U.S., both of which mimic a form of THC (tetrahydrocannabinol), the compound responsible for the "high" of recreational cannabis use. Dronabinol (Marinol) is approved to treat chemotherapy-induced nausea and vomiting in both children and adults, while the pediatric use of nabilone (Cesamet) carries a caution. A third cannabinoid, cannabidiol, is currently in phase 3 trials for treatment of seizures.

The researchers followed established procedures in searching for studies of medical cannabis use listed in major research indexes and selected out those that primarily enrolled participants aged 18 and under and included original data about a clinical use. Only 21 papers reporting on a total of 22 studies met their criteria. The papers were published from 1979 to 2017, 14 within the last five years. Only 5 were randomized controlled trials, the others being case reports, open-label trials, parent surveys or case series. The most common conditions studied were chemotherapy-induced nausea and vomiting (6 studies) and seizures (11 studies).

The trials for chemotherapy side effects -- 4 of which were randomized controlled trials -- found that medical cannabis was significantly better than anti-nausea drugs standard at the time of study for reducing nausea and vomiting. Similarly the epilepsy studies, including a single randomized trial, found that medical cannabis reduced the frequency of seizures in participants, some with treatment-resistant seizures. Limitations of these studies include lack of a control group for many, small sample size, differences in the medications used and lack of long-term follow-up.

Two studies investigating the use of cannabis for spasticity and three case report on use for neuropathic pain, post-traumatic stress disorder or Tourette syndrome all lacked controls or blinding, conferring a high risk of biased findings. "At this time," Wong says, "we do not have good evidence that cannabis can be useful in children and adolescents for any conditions other than seizures or chemotherapy-induced nausea and vomiting."

He and Wilens also note that decisions regarding medical cannabis use need to weigh the likely benefits against the known risks, which -- based on the results of studies in recreational cannabis users -- are probably even greater for children and adolescents. Their still-developing brains may make them even more vulnerable than adults to cannabis's negative effects on learning, memory, attention and problem solving. Additional research is needed to better understand the risks and long-term effects of cannabis-based drugs in this population.

When asked how he would advise the parents of a child with a condition that could be alleviated with medical cannabis, Wong states, "I would recommend they have a thorough discussion of the risks and benefits with a physician who has specialized knowledge and experience in the area. For chemotherapy side effects, that could be a pediatric oncologist or palliative care specialist; for seizures, that could be a pediatric neurologist, especially at an academic medical center involved in the ongoing clinical trials of medical cannabis for seizure disorders."

https://www.sciencedaily.com/releases/2017/10/171023094606.htm

Cannabis consumption increases violent behavior in young people in psychiatric care

October 6, 2017

Science Daily/University of Montreal

A new study by researchers at the Institut en santé mentale de Montréal demonstrates that sustained used of cannabis is associated with an increase in violent behaviour in young people after discharge from a psychiatric hospital.

The research by Dr. Alexandre Dumais (MD, PhD, FRCPC, psychiatrist at the Institut Philippe Pinel) and Dr. Stéphane Potvin (PhD, professor at the Université de Montréal), which studied 1,136 patients (from 18 to 40 years of age) with mental illnesses who had been seen five times during the year after discharge, took into account substance use and the onset of violent behaviour.

Previous research has already shown that a cannabis use disorder is associated with violent behaviour. According to this new study published in Frontiers in Psychiatry, users who reported at each follow-up visit that they continued to smoke cannabis presented an increased risk (+144%) of violent behaviour.

These results also confirm the detrimental role of chronic cannabis use in patients with mental illness. According to the principal researcher Alexandre Dumais (MD, PhD, FRCPC): "an interesting feature of our results is that the association between persistent cannabis use and violence is stronger than that associated with alcohol or cocaine."

Indicator for external follow-up

Persistent cannabis use should therefore be considered as an indicator of future violent behaviour in patients who leave a psychiatric hospital for follow-up in an outpatient clinic, although the researcher points out that this behaviour tends to fade with time.

"This decrease could be explained by better adherence to treatment (the patient becomes more involved in their treatment over time) and by better support from their entourage. Even though we observed that violent behaviour tended to decrease during follow-up periods, the association remained statistically significant," noted Dr. Dumais.

The research results also suggest that there is no reciprocal relationship, that is, the use of cannabis resulted in future violent behaviour and not the reverse (for example, a violent person might use cannabis following an episode of violent behaviour to reduce their tension), as was suggested by previous studies.

The effects of cannabis on the brain

A recent meta-analysis of neuroimaging studies demonstrated that chronic cannabis users have deficits in the prefrontal cortex, a part of the brain that inhibits impulsive behaviour.

These results are important because they offer additional information to young adults, who can evaluate the risks of cannabis before deciding whether or not to use it. They will also serve as a tool to develop strategies to prevent the risk of violence associated with cannabis, since these risks have important consequences, both socially and for the health of young adults and for society in general.

This study was funded by the Fonds de la recherche du Quebec-Santé.

https://www.sciencedaily.com/releases/2017/10/171006164855.htm

Reversing the negative effects of adolescent marijuana use

September 12, 2017

Science Daily/University of Western Ontario

Researchers at Western University have found a way to use pharmaceuticals to reverse the negative psychiatric effects of THC, the psychoactive chemical found in marijuana. Chronic adolescent marijuana use has previously been linked to the development of psychiatric diseases, such as schizophrenia, in adulthood. But until now, researchers were unsure of what exactly was happening in the brain to cause this to occur.

"What is important about this study is that not only have we identified a specific mechanism in the prefrontal cortex for some of the mental health risks associated with adolescent marijuana use, but we have also identified a mechanism to reverse those risks," said Steven Laviolette, professor at Western's Schulich School of Medicine & Dentistry.

In a study published online today in Scientific Reports the researchers demonstrate that adolescent THC exposure modulates the activity of a neurotransmitter called GABA in the prefrontal cortex region of the brain. The team, led by Laviolette and post-doctoral fellow Justine Renard, looked specifically at GABA because of its previously shown clinical association with schizophrenia.

"GABA is an inhibitory neurotransmitter and plays a crucial role in regulating the excitatory activity in the frontal cortex, so if you have less GABA, your neuronal systems become hyperactive leading to behavioural changes consistent with schizophrenia," said Renard.

The study showed that the reduction of GABA as a result of THC exposure in adolescence caused the neurons in adulthood to not only be hyperactive in this part of the brain, but also to be out of synch with each other, demonstrated by abnormal oscillations called 'gamma' waves. This loss of GABA in the cortex caused a corresponding hyperactive state in the brain's dopamine system, which is commonly observed in schizophrenia.

By using drugs to activate GABA in a rat model of schizophrenia, the team was able to reverse the neuronal and behavioural effects of the THC and eliminate the schizophrenia-like symptoms.

Laviolette says this finding is especially important given the impending legalization of marijuana in Canada. "What this could mean is that if you are going to be using marijuana, in a recreational or medicinal way, you can potentially combine it with compounds that boost GABA to block the negative effects of THC."

The research team says the next steps will examine how combinations of cannabinoid chemicals with compounds that can boost the brains GABA system may serve as more effective and safer treatments for a variety of mental health disorders, such as addiction, depression and anxiety.

https://www.sciencedaily.com/releases/2017/09/170912134809.htm

CBD may protect against psychiatric risk from high-THC cannabis strains

Neuroscientists find cannabidiol reduces symptoms such as impaired memory in adolescent mice simultaneously exposed to THC

September 6, 2017

Science Daily/Indiana University

A study reported Sept. 5 by neuroscientists at Indiana University finds that a non-psychoactive compound in cannabis called cannabidiol, or CBD, appears to protect against the long-term negative psychiatric effects of THC, the primary psychoactive ingredient in cannabis.

Other research has shown that long-term use of cannabis increases adolescent drug users' risk for certain psychiatric and neurological disorders, such as schizophrenia. The risk to teens is greater than ever since selective breeding of plants to produce higher levels of THC over the past several decades has substantially increased exposure to the compound.

"This study confirms in an animal model that high-THC cannabis use by adolescents may have long-lasting behavioral effects," said lead author Dr. Ken Mackie, professor in the IU College of Arts and Sciences' Department of Psychological and Brain Sciences and director of the Linda and Jack Gill Center for Biomolecular Science at IU Bloomington. "It also suggests that strains of cannabis with similar levels of CBD and THC would pose significantly less long-term risk due to CBD's protective effect against THC."

THC, or tetrahydrocannabinol, is the chemical in cannabis that causes the "high" experienced during its use. Cannabis with higher levels of THC possess lower levels of the protective CBD, and vice versa, due to a biological link between THC and CBD production in the plant. An analysis of cannabis seized by the U.S. Drug Enforcement Administration found that while THC levels rose 300 percent from 1995 to 2014, the levels of CBD have declined 60 percent.

In contrast to THC, CBD does not cause a "high." It is also an important ingredient in medical cannabis. For example, CBD appears useful as a treatment for some forms of severe childhood epilepsy, and its use for severe epilepsy was approved by the Indiana legislature this year.

"This is the first study in a rigorously controlled animal model to find that CBD appears to protect the brain against the negative effects of chronic THC," Mackie said. "This is especially important since heavy use of cannabis with higher levels of THC poses a serious risk to adolescents."

To conduct their study, IU researchers divided adolescent or adult male mice into five groups. Three groups received 3 milligrams per kilogram of body weight of either THC, CBD, or THC with CBD every day for three weeks. The other two groups received a placebo or no treatment.

All mice were then tested for signs of impaired memory, obsessive-compulsive behaviors and anxiety immediately following treatment as well as six weeks after treatment.

The mice exposed to THC alone showed signs of impaired memory and increased obsessive-compulsive behavior immediately after treatment. The adolescent group still experienced these changes six weeks after treatment, whereas the adult group did not. Both groups experienced a long-term increase in anxiety.

By contrast, adult and adolescent mice exposed to CBD alone showed no behavioral changes immediately or six weeks after treatment. Most significantly, mice in both age groups that received CBD with THC exhibited no short- or long-term behavioral changes. These results suggest that long-term use of cannabis strains containing similar amounts of CBD and THC may be less harmful than long-term use of high-THC strains.

https://www.sciencedaily.com/releases/2017/09/170906135554.htm

Marijuana use amongst youth stable, but substance abuse admissions up

August 15, 2017

Science Daily/Binghamton University

While marijuana use amongst youth remains stable, youth admission to substance abuse treatment facilities has increased, according to new research from Binghamton University, State University of New York.

Miesha Marzell, assistant professor of social work at Binghamton University, along with researchers at The University of Iowa, did a secondary analysis of data collected from every nationally funded substance abuse treatment facility in the United States from 2003-2013. The data covered admissions before and after major marijuana policies were enacted nationwide. The team's analysis showed that while marijuana use amongst youth has remained relatively unchanged, admissions to substance abuse treatment facilities has increased.

"Teens were being admitted to substance abuse treatment centers across the United States, but they were not necessarily indicating that their marijuana use was at a high-risk," said Marzell.

As to why numbers are up, Marzell says that it could be that people are seeing any kind of use as high-risk and want to make sure that, from a prevention standpoint, that they stay on top of it.

"As states legalize, it provides a different access to this drug. It could be that people are reporting any type of use now as risky, whereas before it wasn't on the minds of people as much," she said.

While Marzell notes that any marijuana that a youth does is illegal and high-risk, experimenting with one joint, for example, doesn't necessarily warrant substance abuse treatment. Marzell said that placing youth in substance abuse treatment unnecessarily can have negative impacts on their life trajectory, as they can be stigmatized.

"It might not be the best course of action for a drug behavior. If you get a splinter, you don't put a cast on; if you break your arm, you put a cast on. It's this overreaction. And it's also not a good use of funds, because treatment is expensive...We want to make sure that we're using all of our resources in an appropriate way," she said.

Marzell said that as marijuana laws continue to change around the country, more research needs to be conducted.

"I think that what needs to be done is more research on changing marijuana policies and youth behavior and outcomes specifically related to treatment. There needs to be more drug education, but substance abuse treatment might not necessarily be warranted," she said.

https://www.sciencedaily.com/releases/2017/08/170815120537.htm

High use of electronic cigarettes seen in 8th-9th graders in Oregon

Rates of e-cigarette use among Oregon 8th & 9th graders is higher than national samples, and that e-cigarette use is closely linked with marijuana and other tobacco use

August 14, 2017

Science Daily/Oregon Research Institute

A study at Oregon Research Institute (ORI) shows that rates of electronic cigarette (e-cigarette) use among Oregon 8th and 9th graders is higher than seen in national samples, and that e-cigarette use is closely linked with use of marijuana and other tobacco products. Led by ORI scientist Erika Westling, Ph.D., study investigators examined e-cigarette prevalence rates in 8th graders and tracked early usage patterns from 8th grade through 9th grade, the first year of high school. Westling and her team also examined gender, ethnicity, and the use of other substances. Study results were recently published in the June 2017 issue of the Journal of Adolescent Health.

The study showed that adolescents are using e-cigarettes at high rates, and many are using e-cigarettes before trying regular cigarettes or chewing tobacco. In addition, e-cigarette users were more likely to have used and be using other substances, with marijuana being the most common. At the beginning of the study, 27.7% of 8th grade students reported some use of e-cigarettes and 16.8% were current users. By the spring of 9th grade, 31.4% of students had used e-cigarettes and 17.4% were current users.

"We found that e-cigarettes were being used at much higher rates than conventional cigarettes," noted Westling, "and about 5% of students were using e-cigarettes daily in the 9th grade, which suggests addiction to nicotine via e-cigarettes in these young adolescents."

The research team surveyed 1100 Oregon students from seven school districts once at the end of 8th grade and three times across 9th grade. Results indicated there were no significant gender or ethnicity differences in prevalence of use in 8th grade or in accelerated usage rates through 9th grade. Males, females, Hispanics, and non-Hispanics were at equal risk for trying and escalating use of e-cigarettes over time. This reveals the broad appeal, access, and popularity of e-cigarettes to this population, and indicates that anti-e-cigarette marketing strategies should target all of these groups.

"Our data was collected prior to regulation of e-cigarettes by the Food and Drug Administration (FDA). There are currently no limits on advertising, flavorings, or e-liquid content, and e-cigarettes are being heavily marketed to youth," said Westling. "Given the high rates of use and previous marketing efforts, youth access to and willingness to use c-cigarettes may not be easily changed."

The FDA finalized the "deeming" rule effective August 8, 2016 to regulate new tobacco products, including e-cigarettes, which will likely result in product standards and prevent misleading claims about the relative risk of tobacco products in the future. However, these regulations will not be in effect for several more years. Currently, the majority of adolescents perceive e-cigarettes as having minimal risks to health or addiction. Only a quarter of high school students know that e-cigarettes typically contain nicotine. Young adolescents are especially vulnerable to nicotine addiction, and symptoms of addiction in adolescence predict regular smoking in emerging adulthood. A recent Surgeon General's report on e-cigarettes and youth notes that there are significant known deleterious health effects resulting from nicotine exposure in adolescence, including changes to the developing brain.

https://www.sciencedaily.com/releases/2017/08/170814143101.htm

Compound derived from marijuana interacts with antiepileptic drugs

August 7, 2017

Science Daily/Wiley

New research published in Epilepsia, a journal of the International League Against Epilepsy (ILAE), suggests that an investigational neurological treatment derived from cannabis may alter the blood levels of commonly used antiepileptic drugs. It is important for clinicians to consider such drug interactions during treatment of complex conditions.

Cannabidiol (CBD), a compound developed from the cannabis plant, is being studied as a potential anticonvulsant, and it has demonstrated effectiveness in animal models of epilepsy and in humans. An ongoing open label study (Expanded Access Program) conducted by investigators at the University of Alabama at Birmingham is testing the potential of CBD as a therapy for children and adults with difficult to control epilepsy. The study includes 39 adults and 42 children, all of whom receive CBD.

Because all of the participants are also taking other seizure drugs while they are receiving the investigational therapy, investigators checked the blood levels of their other seizure drugs to see if they changed. "With any new potential seizure medication, it is important to know if drug interactions exist and if there are labs that should be monitored while taking a specific medication," said lead author Tyler Gaston, MD.

Dr. Gaston and her colleagues found that there were significant changes in levels of the drugs clobazam (and its active metabolite N-desmethylclobazam), topiramate, and rufinamide in both adults and children, and zonisamide and eslicarbazepine in adults only. Except for clobazam/desmethylclobazam, however, the drug levels did not change outside of the normally accepted range. In addition, adult participants in the study taking clobazam reported sedation more frequently.

Tests also showed that participants taking valproate and CBD had higher ALT and AST (liver function tests) compared with participants not taking valproate. Very high ALT and AST indicate abnormal liver function, but significant ALT and AST elevation occurred only in a mall number of participants (4 children and 1 adult), and the levels returned to normal after discontinuation of valproate and CBD.

"While the interaction between CBD and clobazam has been established in the literature, there are currently no published human data on CBD's potential interactions with other seizure medications," said Dr. Gaston. "However, given the open label and naturalistic follow-up design of this study, our findings will need to be confirmed under controlled conditions."

The findings emphasize the importance of monitoring blood levels of antiepileptic drugs as well as liver function during treatment with CBD. "A perception exists that since CBD is plant based, that it is natural and safe; and while this may be mostly true, our study shows that CBD, just like other antiepileptic drugs, has interactions with other seizure drugs that patients and providers need to be aware of," said Dr. Gaston.

https://www.sciencedaily.com/releases/2017/08/170807080803.htm

Pattern of marijuana use during adolescence may impact psychosocial outcomes in adulthood

July 25, 2017

Science Daily/University of Pittsburgh Schools of the Health Sciences

A pattern of escalating marijuana use in adolescents is linked to higher rates of depression and lower educational accomplishments in adulthood.

How an adolescent uses marijuana, in particular a pattern of escalating use, may make an adolescent more prone to higher rates of depression and lower educational accomplishments by the time they reach adulthood. Those findings come from a new study led by researchers from the Department of Psychiatry at the University of Pittsburgh School of Medicine and Pitt Department of Psychology published in the journal Addiction.

"We know that cannabis use in adolescence is associated with outcomes like lower educational level, and difficulties with mood and depression, but through this long-term study, we've been able to provide a much deeper insight into this relationship, showing that certain characteristics of use may be more important than others," said Erika Forbes, Ph.D., professor of psychiatry, psychology and pediatrics, and lead author of the study. "The findings highlight that understanding marijuana use across the entire period of adolescence, which we know is an extremely vulnerable developmental phase, may tell us much more about detrimental long-term impacts than knowing about overall or one time use."

Researchers analyzed 158 boys and young men from Pittsburgh who were part of The Pitt Mother & Child Project (PMCP), a long-running longitudinal study of males at high risk for antisocial behavior and other psychopathology based on low income, family size and child gender, led by Daniel Shaw, Ph.D., distinguished professor of psychology at the University of Pittsburgh.

At age 20, the young men self-reported annual cannabis use characteristics for every year since they started use during an interview. Each man's brain was also scanned using fMRI to assess functional connectivity in the brain's reward circuit. The study participants completed questionnaires at ages 20 and 22 that examined psychosocial outcomes measuring depression and educational attainment.

The researchers analyzed frequency of cannabis use from ages 14 to 19 to determine the relationship between use during adolescence and psychosocial outcomes. In an unexpected finding, boys who started occasionally using cannabis around 15 or 16 years old and had a dramatic increase in use by the time they were 19 had the greatest dysfunction in brain reward circuitry, the highest rates of depression and the lowest educational achievements.

"We expected to see that the young men who had a high, consistent level of marijuana use would have differences in brain function. However, it turned out that those who had an increasing pattern of use over their teens had the biggest differences," Forbes added.

"Though the results do not show a direct causal link, it's important to note that even though most people think marijuana isn't harmful, it may have severe consequences for some people's functioning, education and mood," Forbes said. "While that may seem unimportant at age 20, the level of education you receive will likely have a huge effect on your quality of life and socioeconomic status later in adulthood."

https://www.sciencedaily.com/releases/2017/07/170725083652.htm

Marijuana and vulnerability to psychosis

July 5, 2017

Science Daily/University of Montreal

The link between marijuana use and psychotic-like experiences has been confirmed in a Canadian adolescent cohort.

Going from an occasional user of marijuana to a weekly or daily user increases an adolescent's risk of having recurrent psychotic-like experiences by 159%, according to a new Canadian study published in the Journal of Child Psychology and Psychiatry. The study also reports effects of marijuana use on cognitive development and shows that the link between marijuana use and psychotic-like experiences is best explained by emerging symptoms of depression.

"To clearly understand the impact of these results, it is essential to first define what psychotic-like experiences are: namely, experiences of perceptual aberration, ideas with unusual content and feelings of persecution," said the study's lead author, Josiane Bourque, a doctoral student at Université de Montréal's Department of Psychiatry. "Although they may be infrequent and thus not problematic for the adolescent, when these experiences are reported continuously, year after year, then there's an increased risk of a first psychotic episode or another psychiatric condition."

She added: "Our findings confirm that becoming a more regular marijuana user during adolescence is, indeed, associated with a risk of psychotic symptoms. This is a major public-health concern for Canada."

What are the underlying mechanisms?

One of the study's objectives was to better understand the mechanisms by which marijuana use is associated with psychotic-like experiences. Bourque and her supervisor, Dr. Patricia Conrod at Sainte Justine University Hospital Research Centre hypothesized that impairments in cognitive development due to marijuana misuse might in turn exacerbate psychotic-like experiences.

This hypothesis was only partially confirmed, however. Among the different cognitive abilities evaluated, the development of inhibitory control was the only cognitive function negatively affected by an increase in marijuana use. Inhibitory control is the capacity to withhold or inhibit automatic behaviours in favor of a more contextually appropriate behaviour. Dr. Conrod's team has shown that this specific cognitive function is associated with risk for other forms of substance abuse and addiction.

"Our results show that while marijuana use is associated with a number of cognitive and mental health symptoms, only an increase in symptoms of depression -- such as negative thoughts and low mood -- could explain the relationship between marijuana use and increasing psychotic-like experiences in youth," Bourque said.

What's next

These findings have important clinical implications for prevention programs in youth who report having persistent psychotic-like experiences. "While preventing adolescent marijuana use should be the aim of all drug strategies, targeted prevention approaches are particularly needed to delay and prevent marijuana use in young people at risk of psychosis," said Patricia Conrod, the study's senior author and a professor at UdeM's Department of Psychiatry.

Conrod is optimistic about one thing, however: the school-based prevention program that she developed, Preventure, has proven effective in reducing adolescent marijuana use by an overall 33%. "In future programs, it will be important to investigate whether this program and other similar targeted prevention programs can delay or prevent marijuana use in youth who suffer from psychotic-like experiences," she said. "While the approach seems promising, we have yet to demonstrate that drug prevention can prevent some cases of psychosis."

A large youth cohort from Montreal

The study's results are based on the CIHR-funded Co-Venture project, a cohort of approximately 4,000 adolescents aged 13 years old from 31 high schools in the Greater Montreal area. These teens are followed annually from Grade 7 to Grade 11. Every year they fill out computerized questionnaires to assess substance use and psychiatric symptoms. The teens also complete cognitive tasks to allow the researchers to evaluate their IQ, working memory and long-term memory as well as their inhibitory control skills.

To do their study, the research team first confirmed results from both the United Kingdom and Netherlands showing the presence of a small group of individuals (in Montreal, 8%) among the general population of adolescents who report recurrent psychotic-like experiences. Second, the researchers explored how marijuana use between 13 and 16 years of age increases the likelihood of belonging to the 8%. Finally, they examined whether the relationship between increasing use of marijuana and increasing psychotic-like experiences can be explained by emerging symptoms of anxiety or depression, or by the effects of substance use on developing cognitive abilities.

https://www.sciencedaily.com/releases/2017/07/170705104042.htm