This week, a published study announced that potent cannabis significantly increases the risk of psychosis. So much so, found the authors of The Lancet paper, that around 30% of first-episode psychosis experiences in London and 50% of those in Amsterdam could be prevented if high-potency cannabis were not available in those cities. Those findings are of course concerning, and they’re part of a body of work showing the link between marijuana and poor mental health: Earlier research found cannabis is associated with psychotic symptoms, such as paranoia; scientists issued a public health warning about the drug in 2016; and a recently published book on marijuana, Tell Your Children, highlights a 2013 paper that found a link between weed and violence, as well as increased rates in violence in the state of Washington shortly after it legalized weed in 2012. Ultimately, though, they’re far from conclusive. One major question is whether cannabis causes psychosis, or if those who are predisposed to psychosis are also more likely to seek out marijuana. So far, evidence points in both directions. Some research suggests cannabis both increases the likelihood of schizophrenia, and that those with the mental condition tend to use marijuana more than the general population. Meanwhile, a 2017 study showed that there’s a genetic overlap between tendency for cannabis use and schizophrenia. It’s also important to note that the Lancet paper focused on daily users of high-potency cannabis, rather than those who only smoke occasionally; as might be expected, some of the clearest evidence of risk, such as the recent Lancet paper, focuses on heavy users. Furthermore, the authors point out that many daily users did not develop a psychotic disorder; their findings on the percentage of psychosis cases that could be prevented is based on statistical analysis, but further work is necessary to identify the other relevant factors. Since marijuana remains illegal in much of the world, there are major regulation and restrictions around researching it. So scientists really don’t yet know as much as they should. There’s also evidence that the drug causes benefits: there’s considerable evidence that it can treat chronic pain and insomnia, for example, and the US Food and Drug Administration has approved a cannabinoid to treat a form of epilepsy. Incredibly, Harvard scientists recently found that smoking weed is associated with a higher sperm count, though further research is needed to determine exactly how cannabis affect fertility. Overall, few drugs come without risks and there is certainly considerable evidence that cannabis is associated with psychosis. But marijuana’s reputation in North America and Western Europe has veered between the hippy conception of the drug a natural risk-free medicine, and 1970s conservative politicians’ view that weed is a highly dangerous substance that causes criminality. The truth is somewhere in between.<doc-sep>(CNN) — Legalization of marijuana, both for medical and recreational use, continues to spread across the globe even as the possible health risks (or benefits) are not fully known. Case in point, according to new research, people who use cannabis daily, as well as those who use high-potency weed, may be three times more likely to develop psychotic disorder than never-users. Published Tuesday in the journal the Lancet Psychiatry, the new evidence is consistent with previous experiments that suggest heavy use and high THC concentration cannabis – a 10% concentration of THC (the psychoactive substance within cannabis) or higher – can be harmful to mental health. “Psychotic disorder,” precisely, is what was studied, said Dr. Marta Di Forti, lead author and a clinician scientist at the Institute of Psychiatry, Psychology & Neuroscience, King’s College London. “We are talking about people who meet diagnostic criteria [and] come to the attention of mental health services to receive treatment for psychosis. So they have to have symptoms of psychosis across the spectrum – so hallucination, delusion – that have lasted at least for a week.” Daily use of cannabis Currently, medical cannabis is legal in most European countries, though recreational use is only legal in the Netherlands, Spain (under certain conditions), and Czech Republic. Many countries, though, are discussing legalization. In the United States, 10 states and the District of Columbia allow recreational sales of marijuana, while 34 states allow medical marijuana use. To understand whether there’s a connection between cannabis and psychosis, Di Forti and her co-authors looked at data from five countries in Europe – the UK, the Netherlands, France, Spain and Italy – and Brazil, where cannabis is illegal. They found 901 patients with a first-time episode of psychosis over a five-year period and compared them to 1,237 matched non-patients. Daily use of cannabis was more common among patients with psychosis compared to the controls, they found. About 30% of patients reported using cannabis daily compared to just 7% of non-patient controls. And use of high potency cannabis was also more common among patients than controls: 37% compared to 19%. Overall, people who used marijuana on a daily basis were three times more likely to have a first episode psychosis compared with people who never used weed, the researchers estimated. And this increased to five times more likely for those who daily used high-potency cannabis. “High-potency cannabis contributes to incidence of psychotic disorder but doesn’t explain it completely,” explained Di Forti, noting that only some users develop a psychotic disorder and the reasons why not all cannabis users are equally susceptible is unclear. Still, the new study may be helpful with regard to medicinal cannabis, since some of those products may include small amounts of THC. For example, maybe psychosis should be listed among the potential side effects, she said. The study results do not provide enough information for her to say “use only this amount, only this often” to remain safe. Still, she and her co-authors estimated that one in five new cases of psychosis may be linked to daily cannabis use, and one in 10 cases linked to use of high potency cannabis. Dr. Robin Murray, senior author of the study and a professor of psychiatric research at the Institute of Psychiatry, Psychology & Neuroscience at King’s College London, said that “15 years ago nobody thought cannabis increased the risk for psychosis.” Only gradually has evidence come out and shown that to be true, he said. Gradually, too, other explanations have been chipped away, he said: For example, some people might say that perhaps a genetic predisposition to schizophrenia led some people to use cannabis and this is the reason for higher rates of psychosis. But a study from Finland rules this out, said Murray: “There may be some genetic component but it’s not the major reason.” In light of the new results, is legalized cannabis a good idea? “Personally, I think it’s much more important that people are educated,” said Murray. “Tobacco is legal, but we’ve seen the consumption plummet because there’s been a sustained educational campaign.” ’The results need to be taken seriously’ Dr. Michael Bloomfield, head of the Translational Psychiatry Research Group and a psychiatrist at University College London, told Science Media Centre that the new study is both “important and well conducted research” that “adds weight to the advice that people who use cannabis recreationally should avoid high-THC cannabis.” Bloomfield was not involved in the new study. Nor was Dr. Adrian James, registrar at the Royal College of Psychiatrists, who told Science Media Centre that the research is “good quality” and “the results need to be taken seriously.” “Cannabis carries severe health risks and users have a higher chance of developing psychosis,” said James. “The risks are increased when the drug is high in potency, used by children and young people and when taken frequently.” Dr. Philip McGuire, a professor of Psychiatry & Cognitive Neuroscience at King’s College London, told CNN that the study’s finding that cannabis use is higher among patients with psychosis is “not itself new.” Still the study “involves relatively large numbers of subjects and has controlled for other risk factors that might have accounted for the results” and in that way adds to what is known about marijuana, said McGuire, who played no part in the new research. Cannabis contains two ingredients that have opposite effects on psychosis: THC induces psychotic symptoms and cannabidiol, known as CBD, reduces them, he explained. His own research has shown that “if healthy volunteers are given THC this induces transient psychotic symptoms like paranoia. However, if volunteers are given CBD beforehand, this blocks the induction of psychotic symptoms by THC,” said McGuire. McGuire and his co-researchers found that adding CBD to regular antipsychotic medication reduced psychotic symptoms in patients with schizophrenia. “When we used brain scanning to measure the effects of CBD and THC on brain function, we found that they have opposite effects on brain activity, which may explain why they have opposite effects on psychotic symptoms,” he said. Get CNN Health's weekly newsletter Sign up here to get The Results Are In with Dr. Sanjay Gupta every Tuesday from the CNN Health team. “The net effect of cannabis that contains both THC and CBD depends on the relative amounts of each,” he explained. “The cannabis that was available in the 1960s was relatively low in THC and high in CBD. However, these days illicit cannabis is often ‘high potency,’ with a high THC content and a low CBD content.” “We are currently conducting research to define the ratio of CBD:THC in cannabis that is optimal for minimizing its psychotic effects,” he said.<doc-sep>Marijuana’s usefulness in helping treat epilepsy and PTSD has helped rebrand the drug as one that can benefit human health. But a link between marijuana and psychosis, a mental disorder associated with severe delusions or hallucinations, still persists, and the research on it has been inconclusive so far. On Tuesday in The Lancet Psychiatry, researchers provide a new glimpse into how strong that connection really is using data on the marijuana habits of psychosis patients from across Europe and Brazil. The evidence and arguments linking marijuana to psychosis is controversial. Previous scientific research has linked THC, marijuana’s psychoactive component, with psychosis in some patients — but not all of them. Why does weed seem to be linked to psychosis in some people and not others? Marta Di Forti, Ph.D., the lead author of the new Lancet paper, argues that the amount and potency of marijuana are important factors in understanding the drug’s connection to psychosis. "This effect was greater in London and in Amsterdam, where high potency is more available. In their analysis of the marijuana habits of psychosis patients across Italy, Spain, the UK, the Netherlands, France, and one site in Brazil, the authors show that one in every five psychosis cases in the study sample was linked to smoking daily, and that one in every ten new cases was linked to smoking marijuana with a THC concentration above 10 percent. “We clearly showed that across the 11 study sites, those who use high potency on daily bases have over a 4 fold increase in the odds of having a psychotic disorder,” Di Forti tells Inverse. “This effect was greater in London and in Amsterdam, where high potency is more available.” Smoking potent marijuana every day was associated with psychosis in this study GIPHY Marijuana Potency and Psychosis Cases In the study, Di Forti and her team tracked how often patients smoked marijuana and estimated the potency of the marijuana based on national data that reported “expected concentrations.” They classified marijuana as “highly potent” if it had a THC concentration of ten percent or more. Then, they compared the smoking habits of the psychosis patients against those of healthy controls from each area. "Both measure how much of cannabis’s active ingredient, THC, reaches our brain. The psychosis patients generally reported significantly more daily smoking and higher rates of potent use. After pooling and reanalyzing this data, Di Forti found her key statistic: Daily cannabis users had a 3.2 times greater chance of having psychosis than people who had never smoked. Those who smoked the “potent” strains of marijuana every day had 4.8 times greater odds of having psychosis. Di Forti says that frequency and potency of marijuana are ultimately two metrics for measuring the same thing: getting THC into the brain. “Both measure how much of cannabis’s active ingredient, THC, reaches our brain,” she explains. “It is a little bit like alcohol. You can reach the same number of units per week either by drinking spirits or lots of wine daily.” In this case, you could think of smoking the potent strains of weed every day as taking daily THC shots. Doing that consistently, at least going by the results in this paper, seems to be associated with greater risks of psychosis. What This Paper Can’t Prove: In an companying commentary Suzanne Gage, Ph.D., a lecturer in psychology at the University of Liverpool, points out that Di Forti’s paper does not establish the causal link that some may hope it does. At its core, it is still an observational study, and though Gage admits that the authors did their best to account for potential confounders, she says there will always be some grey area. "It’s very definitively hard to say ‘yes, cannabis causes psychosis.’ “There’s lots of this observational data that suggests this link, but it’s very definitively hard to say, ‘Yes, cannabis causes psychosis,’” she tells Inverse. “It’s definitely not the case that everyone who uses cannabis every day will develop psychosis, so it just makes the pattern quite complicated. People who choose to use high potency cannabis every single day are likely to be different from people who don’t in lots of ways other than just their cannabis use.” Part of the reason the data to make a strong link are inadequate is because psychosis cases remain rare, despite marijuana use becoming increasingly common. To add to that, there’s still a lot we don’t understand about psychosis as well as all the different bioactive components of marijuana. CBD, the non-psychoactive component in marijuana, has actually been shown to help treat psychosis and other psychiatric symptoms. And as far as psychosis goes, says Gage, other factors like childhood trauma or a family history of psychosis can affect who actually ends up with the condition. Nevertheless, the new paper is valuable because it provides more evidence to support the idea that there is a pattern between marijuana use and psychosis — one that warrants further investigation. But the more we learn about all the different effects of marijuana, and the hundreds of different components, it’s becoming clear that we don’t know what kind of pattern it really is. As research on the mental health-marijuana connection continues, we could soon find out whether it’s part of a far more complicated picture. Abstract Cannabis use is associated with increased risk of later psychotic disorder but whether it affects incidence of the disorder remains unclear. We aimed to identify patterns of cannabis use with the strongest effect on odds of psychotic disorder across Europe and explore whether differences in such patterns contribute to variations in the incidence rates of psychotic disorder.<doc-sep>
Credit: CC0 Public Domain High potency cannabis, especially when used daily, is "strongly linked" to the risk of developing psychotic disorders such as schizophrenia and paranoia, scientists said Wednesday. In Amsterdam and London—where high-THC marijuana has long been the rule rather than the exception—50 and 30 percent of new psychosis cases, respectively, were associated with potent forms of the drug. The findings, reported The Lancet, bolster a growing body of research connecting pot to a range of mental health disorders. With piecemeal legalisation and decriminalisation, consumption in North America and Europe has increased markedly over the last two decades, even as levels of the drug's mind-bending molecule, delta-9-tetrahydrocannabinol (THC), have risen four- or five-fold. "The use of cannabis with a high concentration of THC has more harmful effects on mental health than the use of weaker forms," said lead author Marta Di Forti, a professor at the Institute of Psychiatry, Psychology and Neuroscience at King's College London. "Our findings also indicate for the first time how cannabis use affects the incidence of psychotic disorder at a population level." Across 11 European cities or regions, and a 12th in Brazil, one in five new cases of psychosis were associated to daily cannabis use, and one in ten to high potency pot, the study found. Trainwreck, gorilla glue If high-THC cannabis—including strains such as "trainwreck", "gorilla glue", and "hindu kush"—were no longer available, "12 percent of cases of first-episode psychosis could be prevented across Europe," the researchers calculated. In Amsterdam, the incidence of first-time psychosis would likely drop from 38 to 19 per 100,000 people per year, while in London, the number of cases would decline from 46 to 32 per 100,000 people. "As the legal status of cannabis changes in many countries and states, and as we consider the medicinal properties of some types of cannabis, it is of vital public health importance to consider the potential adverse effects that are associated with daily cannabis use, especially high potency varieties," said Di Forti. The researchers established a baseline by identifying—in the cities and regions examined—all individuals known to have experienced a first episode of psychosis from 2010 to 2015. They found 901 cases. These were then compared to 1,237 healthy adults to tease out the risk factors associated with psychosis. All participants provided information about how frequently they had used marijuana and other drugs over a period of years. The scientists also classified the potency of the cannabis consumed as either "high" (over 10 percent THC) or "low" (under 10 percent THC). In some locations, THC levels are 20 percent or higher, they noted. Nearly 30 percent of patients who had experienced a first episode of psychosis were daily cannabis users, compared with less than seven percent of those in the control group. For high potency pot, the corresponding figures were 37 and 19 percent. Adjusting for social factors and other drug use, the authors found that daily cannabis users were three times more likely to experience psychosis for the first time than people who had never used it. For daily use of high-potency cannabis, this increased to five times. While the correlation between marijuana use and mental disorders was strong, a cause-and-effect relationship can only be inferred, the authors cautioned. However the registrar at the Royal College of Psychiatrists, Adrian James, said the findings were to be "taken seriously," and that his institution "is reviewing the mental health effect of cannabis use." David Nutt, head of the centre for neuropsychopharmacology at Imperial College London, said it was "important to realise that THC is well known to produce psychosis in healthy volunteers—people without a predisposition to mental illness". Explore further Psychosis five times more likely for cannabis users, study finds © 2019 AFP