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Published: 15 April 2026

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A sweeping new study published in The Lancet Psychiatry has reignited a long-running debate about medical cannabis for mental health conditions. The findings make for uncomfortable reading for a fast-growing private prescribing sector that has largely outpaced the science behind it.

Researchers described this as the largest and most comprehensive review of its kind. They analysed 54 randomised controlled trials involving 2,477 participants across a range of mental health and substance use disorders. The central conclusion is stark: for the vast majority of psychiatric conditions where doctors currently prescribe medical cannabis, no reliable evidence exists that it works.

A Booming Market With a Thin Evidence Base

Medical cannabis has been legal on prescription in the United Kingdom since November 2018. High-profile campaigns on behalf of children with treatment-resistant epilepsy initially drove that change. Since then, the market has expanded dramatically. More than 30 specialist cannabis clinics are now registered with the Care Quality Commission in England, serving an estimated 80,000 patients.

The numbers are striking. Between 2023 and 2024, private prescriptions more than doubled, rising from around 283,000 to 659,000. Yet that figure needs context. Patients typically receive repeat prescriptions every four to eight weeks, so those 659,000 prescriptions likely represent roughly 82,000 individuals rather than a surge of entirely new cases.

What is harder to contextualise, however, is the mismatch between who receives medical cannabis prescriptions and what clinical trials actually support. According to available data, approximately 42 per cent of UK medical cannabis patients receive it for psychiatric conditions such as anxiety, depression, post-traumatic stress disorder (PTSD) and obsessive-compulsive disorder (OCD). Notably, the new Lancet Psychiatry review found no significant benefit for any of these conditions.

What the Research Found on Cannabinoids for Mental Disorders

Researchers at the University of Sydney and several partner institutions conducted this systematic review. They examined RCT evidence published between 1980 and May 2025, and what they found was sobering.

For anxiety disorders, including social anxiety, the data showed no significant reduction in symptoms. For PTSD, results were equally discouraging. Furthermore, for psychotic disorders, OCD, bipolar disorder, ADHD and anorexia nervosa, researchers identified no meaningful benefit. Most strikingly, not a single randomised controlled trial has examined cannabinoids for depression.

Cannabinoids did show promise in a few areas. A combination of cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC) reduced withdrawal symptoms and cannabis use in people with cannabis use disorder. Additionally, insomnia patients showed improved sleep time, and those with Tourette’s syndrome experienced a reduction in tic severity. Researchers also recorded a reduction in autistic traits in autism spectrum disorder studies, though they rated this evidence as very low certainty.

Overall, people taking cannabinoids were significantly more likely to experience an adverse event than those on placebo. Specifically, roughly one in every seven patients was affected. The most commonly reported side effects included dry mouth, nausea, diarrhoea and dizziness.

The Prescribing Paradox

The disconnect here is considerable. Sleep problems, anxiety, depression and PTSD rank among the most common reasons people seek medical cannabis in the UK, the US and Australia. Yet the evidence base for these very indications is, at best, weak.

Professor Owen Bowden-Jones, former chair of the Advisory Council for the Misuse of Drugs (ACMD), said the findings give the “clearest indication yet” that benefits of medical cannabis may have been overstated for many conditions.

Defenders of the practice argue the picture is more complicated than clinical trials alone can capture. Dr Niraj Singh, a consultant psychiatrist with over six years of prescribing experience, points to what he describes as outstanding outcomes in patients who had exhausted every other option.

“Tens of thousands of patients would testify that it benefits them across an array of symptoms,” he said. “In my experience, it has had some incredible outcomes.”

The Lancet Psychiatry review deliberately excluded this real-world evidence, drawn from patient registries and observational studies. Authors justified this on methodological grounds: observational data cannot establish causation and is more prone to bias. Nevertheless, critics including Professor David Nutt, founder of the charity Drug Science, have pushed back on the idea that RCTs should hold a monopoly on clinical decision-making.

Medical Cannabis for Mental Health: Safety Is Not Efficacy

Proponents of medical cannabis prescribing often argue that a relatively benign safety profile justifies its use even where efficacy evidence is limited. The review offers some support for this position. While cannabinoid users experienced more adverse events overall, serious adverse events and study withdrawals did not increase significantly.

However, researchers flag a critical caveat. Most clinical trials involved registered, pharmaceutical-grade cannabinoid products. These differ markedly from the high-THC preparations increasingly common in Australian, American and Canadian markets, and becoming more available privately in the UK. Products with high THC content carry well-documented risks of increased anxiety, paranoia and, in vulnerable individuals, psychosis.

Dr Marta Di Forti, professor of drug use, genetics and psychosis at King’s College London, has raised concerns about patients with pre-existing mental health conditions receiving high-THC prescriptions. In her view, those with a history of anxiety, depression or paranoia face a greater risk of worsening symptoms and dependency if exposed to products with THC content of 10 per cent or above.

In response to these concerns, the Medical Cannabis Clinicians Society recommends that prescriptions exceeding 60 grammes per month, or those containing more than 25 per cent THC, go through peer panel review.

The Research Gap Nobody Is Filling

Perhaps the most troubling part of this debate is not what the evidence shows, but what it does not yet examine. Back in 2018, the Department of Health committed to conducting efficacy trials in children with epilepsy. According to Professor Nutt, nothing has been done. Meanwhile, pharmaceutical companies show little interest in a botanical product that cannot be patented.

The Lancet Psychiatry review authors identified 14 ongoing trials through clinical registries that could not yet contribute to the analysis. They call urgently for trials with larger and more representative samples. Importantly, many of the included studies were small, with a median sample size of just 31 participants, which significantly limits what conclusions researchers can draw.

Professor Mike Barnes, chair of the Medical Cannabis Clinicians Society, has been candid that the industry itself bears responsibility here. “The industry has not been rigorous enough in collecting and analysing patient outcomes,” he said. “Clinics have a moral obligation to collect their own data.”

What This Means for Patients Using Medical Cannabis for Mental Health

For the tens of thousands of people in the UK (alone) currently using prescribed medical cannabis for mental health conditions, these findings present a genuine dilemma. Many have tried multiple treatments without success. Others describe the relief they found as life-changing. The United Patients Alliance has warned that dismissing medical cannabis on the basis of incomplete evidence risks pushing patients back to the unregulated illegal market, where product quality, THC content and medical oversight are entirely absent.

That concern deserves to be taken seriously. Even so, it cannot substitute for a proper evidence base. The Lancet Psychiatry review does not claim that medical cannabis never helps any individual. Rather, it argues, carefully and on the available data, that routine prescribing across these indications lacks the clinical trial support we would expect for any other controlled medicine.

Consider the scale of the problem. An estimated 8.7 million people in England received antidepressants in 2023/24. Over 1.5 million adults were in contact with NHS mental health services as of January 2026. The pressure to find better options is entirely understandable. Yet the answer to a struggling mental health system is to invest properly in research that could one day tell us, with confidence, which patients might genuinely benefit and under what conditions.

(Source: WRD News)

Also Read

• Cannabis as ‘Medicine?’: Pot Propaganda, Emotive Anecdote, Marketing Manipulation, and the Side Stepping of Science
• Regulation of Cannabis as Medicinal: Playing the Game of ‘Licensed Credibility’ in a State and Federal Legislation Disconnect.
• Failing Mental Health and ‘Vote for Medicine’ Models: Cannabis Conundrum Grows

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Published: 01 April 2026

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On 25 March 2026, the International Academy on the Science and Impact of Cannabis (IASIC) hosted a presentation by Dr Ragy R. Girgis, M.D., M.S., Professor of Clinical Psychiatry at the Columbia University Department of Psychiatry and the New York State Psychiatric Institute. His subject was cannabis and mass shootings, and the findings come from what is now the most comprehensive mass murder repository ever assembled: the Columbia Mass Murder Database.

The database contains more than 2,300 cases of personal-cause mass murder documented worldwide since 1900. It was not built to prove a point. It was built because Dr Girgis and his colleagues decided they wanted to understand, as definitively as possible, what was actually driving mass shootings rather than relying on assumption, media coverage, or politically convenient narratives.

What it is beginning to reveal about cannabis and mass shootings is not comfortable reading.

Building the Database

Before getting to the findings, it is worth understanding what the Columbia Mass Murder Database actually is, because the rigour of the methodology is what gives the results their weight.

Dr Girgis and his team began by reviewing popular databases of mass murder including Wikipedia, the Stanford database, Mother Jones, Everytown, and others. From those sources they identified potential cases, then excluded anything that did not meet their strict criteria: events had to involve three or more fatalities not including the perpetrator, had to be perpetrated for personal reasons rather than war, terrorism, gang activity or organised crime, and had to be supported by primary sources in English, meaning court and police records or reliable news media rather than secondary websites.

What remained was a dataset of around 1,700 mass murders in the original iteration, now grown to more than 2,300 cases through to 2023 or 2024. It is the largest such dataset in the world.

One of the key design decisions was the use of comparison groups. Most prior research on mass shootings had not included them, which introduced significant bias into the findings. Dr Girgis’s team divided the sample into perpetrators who used firearms and perpetrators who used other methods, on the basis that weapon choice was the most meaningful differentiator between types of mass murder. That comparison structure is what makes the cannabis findings meaningful rather than merely suggestive.

What Most People Get Wrong About Mass Shootings

Before arriving at the cannabis data, Dr Girgis walked through some findings that challenge widely held assumptions.

The first concerns mental illness. Most violence, and most mass shootings, is committed by people without psychotic illness. This is consistent with what the research has long suggested, but it continues to be misrepresented in public debate. Mental illness, specifically psychosis, accounts for roughly 5% of the contributing factors to mass shootings. It is a slice of the pie, not the whole thing.

The second concerns the types of mass shooting people tend to think about. School shootings, which dominate news coverage and public imagination, represent only about 13% of all mass shootings. The most common type, accounting for around 45% of cases, is familicide: mass murder involving a spouse, children, or other family members. The second most common is felony-related mass murder. The public-facing, stranger-targeted mass shooting is actually the least common category, though it attracts the most attention.

The third concerns alcohol. Despite a widespread cultural assumption that alcohol and violence go hand in hand, alcohol misuse showed no meaningful relationship with mass murder in the data. The signal in the data is not about alcohol. It is almost entirely about cannabis.

The Number That Should Prompt Questions

Here is what the data on cannabis and mass shootings actually shows.

In the United States, the prevalence of cannabis involvement among mass shooters before 1996 was around 5%. After 1996, the year medical cannabis was first legalised in California, that figure more than doubled to over 11%. The result was statistically highly significant.

Dr Girgis chose 1996 deliberately, and not arbitrarily. He and his colleagues were aware that using a single date as a policy marker has limitations. So they tested the result using 1990 and 2000 as alternative cutoff years and found the same pattern held. They also noted the well-documented diffusion effect of cannabis laws, whereby legalisation in one state influences use and availability across many others, which further supports the use of a single national date as a meaningful marker.

When the same analysis was applied to perpetrators of mass murder who did not use firearms, there was no increase. No relationship at all. The doubling of cannabis involvement was specific to mass shootings.

That specificity is the most important feature of the finding. It is not simply that cannabis use has increased across the general population since legalisation began, which it has. The relationship shows up specifically in people who used firearms to commit mass murder, and not in a closely comparable group of people who committed mass murder by other means. That is the kind of pattern that, in research terms, begins to suggest something more than coincidence.

Motive, Suicide, and What Cannabis Involvement Tells Us

One of the more revealing findings from the data concerns what cannabis involvement predicts about a perpetrator’s behaviour at the time of the event.

Mass shooters with cannabis involvement were significantly less likely to take their own life at the time of the shooting compared to those without cannabis involvement. To understand why that matters, Dr Girgis explained how researchers think about the barriers that prevent someone from perpetrating a mass murder.

There are three of them. The first is the person’s own moral or value system, whether that is religious, ethical, or psychological in origin. The second is the moral framework they have internalised from the people around them: family, partners, community, society. The third is the rational deterrent of getting caught, prosecuted, and imprisoned.

When a perpetrator plans to die at the scene, that third barrier is removed entirely. It becomes significantly easier, psychologically, to carry out the act. Mass shootings, more than other forms of mass murder, are associated with perpetrators who intend to take their own life, and it is partly for this reason that mass shootings are so much more common than other forms of mass murder involving comparable planning and motivation.

What the cannabis data suggests is that perpetrators with cannabis involvement are operating with a different set of motivations. They are more likely to intend to survive. That changes the profile of the event and potentially the profile of the intervention that might prevent it.

Cannabis involvement was also associated with significantly younger perpetrators. That finding is perhaps less surprising given what is known about cannabis use demographics, but it reinforces the picture of a distinct subgroup of mass shooters for whom cannabis is a meaningful variable.

Correlation, Causation, and What Comes Next

Dr Girgis is precise about the limits of what the data shows. These findings are correlational. Establishing causation would require a randomised clinical trial, which is not feasible in this context. The data cannot tell us that cannabis caused these individuals to commit mass shootings.

What the data can do is establish a specific, statistically significant pattern that is consistent with the broader and well-established body of evidence linking cannabis use and violence more generally. Dr Girgis described that broader evidence as very clear. The relationship between cannabis and violence in general is not contested in the literature. What the Columbia Mass Murder Database adds is a specific examination of that relationship in the context of mass shootings in the United States, with a comparison group designed to account for confounding.

The honest summary is this: cannabis involvement in mass shooters more than doubled after cannabis legalisation began, the relationship is specific to mass shootings rather than mass murder more broadly, and it is consistent with what we already know about cannabis and violence. That is not a finding to dismiss because it is inconvenient.

A Piece of the Pie

Dr Girgis frames the contributing factors to mass shootings as pieces of a pie rather than a single cause. Mental illness accounts for roughly 5%. Recreational drug use, and in this dataset that means almost exclusively cannabis, accounts for another portion. Social, cultural, and situational factors make up the rest.

That framing is important. It resists the temptation to reduce a complex phenomenon to a single explanation, which is exactly what public debate on mass shootings tends to do. After every high-profile shooting, attention immediately focuses on one cause: mental illness, gun laws, social media, school culture. The data suggests the reality is more distributed than that.

But distributed does not mean equal. And a doubling of cannabis involvement among mass shooters following legalisation is not a small signal in a noisy dataset. It is a finding that deserves to be part of the policy conversation.

The Conversation That Keeps Getting Avoided

Cannabis and mass shootings is not a pairing that survives long in public debate. Legalisation is politically popular. The cannabis industry is large and commercially motivated to keep the public narrative positive. And findings like these are easy to dismiss as correlational, preliminary, or simply too uncomfortable to act on.

But the data on cannabis and mass shootings is now emerging from the most rigorous dataset ever applied to this question. Governments expanding cannabis access, and many are, are making long-term decisions about public health without seriously engaging with this research. That is a failure of due diligence dressed up as progress.

Dr Girgis and his colleagues are not campaigners. They are researchers who built a database, applied a comparison structure to control for bias, and reported what they found. That finding is specific: cannabis involvement among mass shooters in the United States more than doubled after legalisation began. It is statistically significant. Moreover, it is consistent with what the broader literature on cannabis and violence already tells us.

The Columbia Mass Murder Database now contains more than 2,300 cases. The pattern around cannabis and mass shootings is clear enough that the question is no longer whether it exists. The question is whether anyone in a position to act on it is paying attention.

Dr Ragy R. Girgis, M.D., M.S., Professor of Clinical Psychiatry, Columbia University Department of Psychiatry and New York State Psychiatric Institute, presented at the IASIC Speaker Series on 25 March 2026. (Source: WRD News)

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Published: 26 March 2026

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A major new study has found that cannabis memory loss goes further than most people expect. Smoking cannabis does not simply blur memories. It can actively distort them, creating false recollections of things that never happened. Washington State University (WSU) researchers say THC, the psychoactive compound in cannabis, disrupts the brain’s ability to store, retrieve, and verify information in ways science is only beginning to map.

The team recruited 120 regular cannabis users and tested them across a wide range of memory tasks. The results raise serious questions about everyday cannabis use, particularly as consumption rises sharply across the UK and North America.

Cannabis Memory Loss Is More Widespread Than Previously Thought

Earlier research on cannabis effects on memory tended to focus on simple tasks, such as recalling a list of words. This study went much further. Researchers tested seven distinct types of memory, from remembering future appointments to tracking where information originally came from.

Out of 21 individual memory measures, cannabis intoxication caused significant impairment on 15. That figure alone tells a striking story. Carrie Cuttler, senior author and associate professor of psychology at WSU, says the findings expose just how broad the problem is.

“Most previous studies have only looked at one or two types of memory, like recalling lists of words,” she said. “This is the first study to comprehensively examine many different memory systems at once, and what we found is that acute cannabis intoxication appears to broadly disrupt most of them.”

How Cannabis Effects on Memory Create False Recollections

The strongest impact appeared in false memory. Researchers played participants lists of related words but left out the key connecting word. Later, those who had consumed THC were far more likely to “remember” words that were never actually said, including words with no connection to the list at all.

“I found it was really common for people to come up with words that were never on the list,” said Cuttler. “Sometimes they were related to the theme of the list, and sometimes they were completely unrelated.”

Cannabis memory loss of this kind goes beyond simple forgetting. The brain stops merely failing to record things accurately. It starts generating plausible replacements. That has real consequences, from misremembering conversations to inaccurately reporting what someone witnessed in an incident.

Source Memory: Losing Track of Where Information Came From

Source memory is the ability to remember not just what you know but where you learnt it. Cannabis users in the study struggled to correctly identify the origin of information they had encountered earlier in the session.

This matters because source memory underpins critical thinking. People who cannot reliably recall whether something came from a trusted expert, a rumour, or something they skimmed online grow more vulnerable to accepting false information as true. Researchers noted this has particular relevance in legal settings, where eyewitness reliability is central to the process.

Everyday Cannabis Effects on Memory: Forgetting What You Planned to Do

The study found clear impairment in prospective memory too. This is the ability to remember future tasks. Taking medication on time, attending a meeting, picking something up on the way home, all of these rely on prospective memory.

“These are things we rely on constantly in our day-to-day lives,” said Cuttler. “If you have something you need to remember to do later, you probably don’t want to be high at the time you need to remember to do it.”

For regular cannabis users, these effects could quietly build into a pattern of missed responsibilities and unreliable follow-through.

Even Moderate Doses Produce Significant Disruption

One finding that genuinely surprised the research team was the dose result. Participants who consumed 20 milligrams of THC performed no better than those who consumed 40 milligrams. Both groups showed similarly poor results compared to the placebo group.

That challenges the common assumption that lower doses carry meaningfully lower risk. Even a moderate amount of cannabis appears sufficient to produce broad cognitive disruption in the short term.

Researchers ran the experiment under rigorous double-blind conditions. Neither participants nor the research team knew who had received THC or a placebo until after the study ended.

What the Study Did Not Find

Episodic content memory, the ability to recall personally experienced events, did not show a statistically significant effect. Cuttler cautioned against reading too much into this finding. The team said further research is necessary before drawing firm conclusions in that area.

Growing Use, Growing Concern

Cannabis is now legal for recreational use across much of North America. Use is also rising across parts of Europe. Yet the research into short-term cognitive risks has lagged behind. Cannabis remains a Schedule I substance under US federal law, which limits how it can be studied.

The WSU Health and Cognition (THC) Lab, co-directed by Cuttler and colleague Ryan McLaughlin, works to close that gap.

“We’re living in a state where cannabis use is very common, but there’s still a lot we don’t know about its acute effects,” said Cuttler. “The goal is to help people make informed decisions about the risks and benefits.”

With 15 out of 21 memory measures showing significant impairment, and false memory and source memory among the hardest hit, cannabis effects on memory appear broader and more consequential than many users realise. Cannabis memory loss is not simply a matter of things slipping your mind. It can mean clearly remembering things that never happened at all. (Source: WRD News)

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Published: 10 March 2026

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Impact of Cannabis and Cannabis Legalization on US Atrial Septal Defect Rates

by  Albert Stuart Reece & Gary Kenneth Hulse - Division of Psychiatry, University of Western Australia, 35 Stirling Hwy., Crawley, WA 6009, Australia

School of Medical and Health Sciences, Edith Cowan University, 27 Joondalup Dr., Joondalup, WA 6027, Australia

10. Xenobiot.2026, 16(2), 43; https://doi.org/10.3390/jox16020043

Abstract

Atrial septal defect (ASD) affects 1:11.3 children in some US states; however, the antecedents of these trends are yet to be identified. A total of 1882 ASD rates (ASDRs) for 2003–2020 were sourced from the National Birth Defects Prevention Network reports. A total of 406,893 ASDs are reported. Substance (cigarettes, binge alcohol, cannabis, cannabinoids, analgesics, cocaine) exposure data were taken from the National Survey of Drug Use and Health. Income and ethnicity data were derived from the US Census. Adjustment was performed by mixed effects, survey and generalized additive regression. Causal analysis was by inverse probability weighting and E-values. Data were analyzed in RStudio. The highest ASDR of 884/10,000 live births was amongst Non-Hispanic Asians and Pacific Islanders in Nevada in 2016–2020. The 2005–2018 median ASDR rose >12-fold in Nevada and New Mexico, >6-fold in New York, and 4.2-fold nationally 1989–2020; it doubled in NY from 2012–2016 to 2016–2020. The average state ASDR rose supra-exponentially (p = 0.0075) and was associated with higher cannabis use states (p = Zero, Cohen’s D = 1.24), apparently driven by cannabis legalization (p = Zero). Estimated exposures to Δ9THC, cannabidiol and cannabigerol were implicated (from p = 2.67 × 10^–68). Cannabis-legal states were compared with others (mean ASDR (C.I.) 178.15 (131.68, 224.62) vs. 74.28 (70.60, 77.96), p = Zero; O.R. 1.82 (1.81, 1.84), E-values 3.04 (lower C.I. 3.02), Cohen’s D 1.29 (0.96, 1.62)). Overall, 29/39 (74.4%) E-value estimates were >4; 39/39 (100%) were >1.25. Cannabis, cannabinoids and cannabis legalization are strong candidates for driving the US ASDR supra-exponentially. Estimates of many cannabinoids, including cannabidiol, Δ9THC, and cannabigerol, are implicated. The results are consistent with other large epidemiological studies. The importance of the results is magnified by the increasing legalization and penetration of cannabinoids into the US population. Since therapeutic abortion is not practiced for ASD, it may be used as a bellwether index of heritable transgenerational cannabinoid genotoxicity and epigenotoxicity associated with cannabinoid exposure.

Keywords: 

cannabis; cannabinoid; congenitalanomalies; cardiogenesis; genotoxicity; epigenotoxicity; transgenerational inheritance; teratogenesis; multigenerational

(Source: https://www.mdpi.com/2039-4713/16/2/43)