Alarming new side effects of smoking cannabis revealed
Researchers have pulled together some of the worrying side effects of smoking cannabis, following a slew of recent studies.
While marijuana is usually seen as low risk by recreational users and can even be legally prescribed in some countries, such as the UK, for certain medical conditions, a lot of research is going into the subject at the moment, revealing new side effects we weren't fully aware of.
For example, just last month, an alarming new study claimed that long-term cannabis use may cause the frontal cortex to thin - the area that's involved in decision-making and executive function.
Meanwhile, another large study found that there is 'very little evidence' that the drug helps most mental health disorders, despite a worldwide surge in people using it for these purposes.
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Now, The Washington Post has outlined some of the ways cannabis may be affecting your brain, as more states in the US are legalising the recreational use of the drug.
Memory issues
The first of which is that it's been linked to worse working memory and can affect your ability to retain new information in the short term.
Joseph Schacht, associate professor of psychiatry and co-director of the Division of Addiction Science, Prevention and Treatment at the University of Colorado School of Medicine, told the publication: “If you smoke cannabis, afterward, if you do a working memory test where you’re trying to maintain some piece of information, like a phone number or a short list of words, you’re less good at doing that while you’re acutely intoxicated."
However, it's not always short-term if you're a regular user.
One January 2025 study found that consistent cannabis users may have lasting memory deficits compared with those who steer clear of the drug.
Scientists looked at how the drug affected more than 1,000 adults ages 22 to 36 using brain imaging and revealed that 'heavy lifetime' users had lower brain activity during a working memory task compared with nonusers.
Meanwhile, another new study, by researchers at Washington State University found that shockingly, smoking cannabis can even make hazy memories feel real when they're actually not.
Researchers conducted a randomized, double-blind, placebo-controlled study to find out which aspects of memory are impaired following acute cannabis use.
Participants were given either real cannabis containing 20 or 40 milligrams of THC, before they completed a battery of memory tests.
It found that cannabis increased susceptibility to false memories and detrimentally impacted a slew of different types of memory, including verbal memory, visuospatial memory, event-cued prospective memory, source memory, and temporal order memory.
Collectively, these groundbreaking results indicate that acute cannabis use has broad detrimental effects on most domains of memory.
Changes in brain volume
Using cannabis for a long time has also been linked to changes in brain volume, especially in those who started using the drug as a teen, when their brain was still developing.
For example, research has identified changes in the white matter of the brain in people who started using cannabis before they reached 16.
White matter is found in the deeper tissues of the brain and contains nerve fibers, which are extensions of nerve cells - it allows the exchange of information and communication.
Schacht explained: “Cannabinoid exposure during that developmental window probably interferes with some of those normal brain development functions."
The Post put together a 2026 meta-analysis of 77 different studies in the journal Addiction, which revealed that cannabis use was linked with reduced volume in the amygdala, which is the region of the brain involved in processing emotions, memory, and decision-making.
Madison Burgess