A comprehensive and systematic review published in August in the Annals of Internal Medicine—the kind that researchers seldom undertake lightly—analyzed 99 studies, spanning 221,097 participants from 1977 through 2023. The report concluded that products containing more than 5 mg THC per serving (over 10 percent) or explicitly labeled as “high-potency concentrate,” “shatter” or “dab” bear strong links to psychosis, schizophrenia and cannabis use disorder—a ravaging drug-related affliction whose symptoms are collectively referred to as CUD. Anxiety and depression were also implicated, though findings were somewhat mixed.
Over the past two decades, THC concentration has skyrocketed.
The implications of the findings extend far beyond academic concern. The legal cannabis market has swelled across the US as well as globally, offering increasingly powerful products once confined to the black market. From waxes and oils to edibles and shatter, ultra-high-THC offerings have become mainstream—yet the brain didn’t evolve to handle these doses. In adolescents and frequent users especially, this chemical onslaught may trigger or exacerbate serious outcomes.
Why does this matter to everyone—from clinicians to policymakers to the curious public? Because the stakes are nothing less than the integrity of our own minds. The review isn’t just a pile of data—it’s a warning bell: When 70 percent of nontherapeutic studies link high-potency THC to psychosis or schizophrenia, and 75 percent to CUD, there’s clearly a pattern. Vulnerable populations—youth, heavy users—are undoubtedly playing with fire by assuming cannabis is benign.
It’s not—by any measure.
One of the main reasons is that, over the past two decades, THC concentration has skyrocketed. In Canada, for instance, average THC in legal dried cannabis rose from about 4 percent in the early 2000s to over 20 percent by 2023—a five-fold increase, according to the Canadian Medical Association Journal. That’s not just stronger weed—it’s a different drug entirely.
One Ontario study of 9.8 million people found those with cannabis-induced psychosis were 241.6 times more likely than the general population to develop schizophrenia within three years—and even those visiting the ER for cannabis use (without psychosis) experienced a 14.3-fold increase in risk.
CUD is no less real than addiction to other substances, and high-THC exposure magnifies the danger. Among daily cannabis users, 10–20 percent develop dependence—and younger age brackets are particularly vulnerable: In April 2025, JAMA Psychiatry reported that heavy cannabis users aged 18–35 exhibited dopamine activity in brain regions similar to that seen in psychosis.
So what’s the takeaway? This: The high-THC cannabis of 2025 is not the mellow herb of a Woodstock dream—it’s a potent psychotropic force with demonstrated capacity to harm minds.
In the end, the review’s alarm bells lead us back to where we began: a brain under siege by concentrated THC.
