A closer look at the viral paper linking cannabis to dementia—and what it actually says (and doesn’t say)

This is a review of:

“Risk of Dementia in Individuals With Emergency Department Visits or Hospitalizations Due to Cannabis” (published in JAMA Internal Medicine, 2024). Study PDF is here

🧵 TL;DR

🚑 A study linked cannabis-related ER visits to higher dementia risk—but only in a very specific population.

🧠 The data doesn’t account for dose, method, reason for use, or underlying cognitive decline.

📉 It’s about correlation, not causation—hospital coding isn’t destiny.

🤔 Mental health comorbidities in the cannabis group were off the charts.

🧪 The takeaway? Be curious, not panicked. Context matters.

Cannabis and Dementia: The Study That’s Raising Headlines—and Eyebrows

Let’s say you go to the ER for a cannabis-related issue. Maybe your edible kicked in late and too strong. Maybe you felt dizzy, anxious, or just plain scared. You’re evaluated, stabilized, and discharged. Somewhere in that chart, your visit is tagged with a cannabis-related diagnosis code.

Fast forward a few years. You develop cognitive symptoms. A dementia diagnosis follows. Now, researchers comb through anonymized health records and find you among others with a similar sequence.

Does that mean cannabis caused your dementia?

That’s the million-dollar question in a new JAMA study out of Ontario. But as usual in cannabis research, the answers aren’t so simple.

🚨 The Study’s Core Claim: Cannabis and Dementia is predicted by ER Visits?

The study tracked over 700,000 adults in Ontario over age 50, comparing those who had an emergency or hospital visit tied to cannabis use (based on ICD-10 billing codes) to matched controls. The cannabis-flagged group showed a 61% higher risk of developing dementia over the following years.

The relative risk sounds dramatic—61% higher—but the absolute numbers remain small: just 20 vs. 15 cases per 1,000 person-years. It’s a statistical bump, not a tidal wave.

On the surface, that’s a big jump. The kind that makes headlines.

But context is everything.

🩺 Who’s in the Cannabis Group, Exactly?

This isn’t your grandmother microdosing for sleep or your neighbor using a THC:CBD tincture for arthritis. This is a population flagged in a hospital database for acute cannabis-related medical crises.

That means:

➕ Panic attacks

➕ Accidental overdosing

➕ Psychosis

➕ Drug interactions

➕ Unmanaged withdrawal

➕ Possibly confounding comorbidities like schizophrenia or bipolar disorder

In fact, psychiatric illness appeared in 21% of the cannabis-exposed group, compared to just 4% of the controls. That’s not a trivial difference. That’s a five-fold red flag.

So is it cannabis? Or is it that people already in trouble are more likely to end up with dementia later?

🔍 What the Study Didn’t Tell Us

This is a classic case of “interesting but incomplete.” Here’s what the study couldn’t tell us:

✔︎ How much cannabis was used—or for how long

✔︎ What type—smoked flower? edibles? high-THC concentrates?

✔︎ Why it was used—was it recreational, self-treatment, or medical?

✔︎ When it was used relative to dementia symptoms

✔︎ How often it was used—or whether it was a one-time incident

✔︎ Whether cannabis was even the main factor in the ER visit

There’s also no accounting for:

✔︎ Education level (a known dementia risk modifier)

✔︎ Head trauma history

✔︎ Chronic loneliness or depression

✔︎ Sleep disturbance (both a cannabis use trigger and a dementia risk factor)

This is like trying to solve a jigsaw puzzle with only the pieces that fit your theory.

🧠 Dementia Is Messy. So Is Cannabis.

Dementia isn’t a switch you flip. It’s the result of dozens of interplaying factors—vascular, metabolic, psychological, environmental, and yes, sometimes pharmaceutical.

Cannabis, too, is hardly a uniform agent. THC and CBD act very differently. Cannabinoids may increase oxidative stress in one context and reduce inflammation in another. Preclinical studies have even shown neuroprotective potential for CBD and CBG, though none of that nuance makes it into this paper.

When you treat cannabis like a monolith—and ignore the realities of aging and chronic illness—you lose the signal in the noise.

⚖️ Correlation ≠ Causation. Especially Here.

This study shows correlation, not causation. Yet its framing implies more than that. The exposed group had hospital-level cannabis issues—by definition, the most extreme cases. To apply those findings to the average user is a leap.

If we did the same study for ibuprofen overdoses or missed insulin doses, we’d find similar future risks—not because those substances are harmful per se, but because hospital-level crises flag people in trouble.

ER visits don’t always predict outcomes. Sometimes, they just reflect underlying vulnerabilities.

🧑‍⚕️ What the Cannabis-Affirming Clinician Sees

If you’re a physician who’s guided thousands of patients through responsible cannabis use, studies like this land with a familiar sting.

It’s frustrating when research lumps in the most extreme, dysregulated cases with everyone else. Cannabis, when used medically, often improves sleep, reduces anxiety, and enhances quality of life—especially in older adults navigating polypharmacy, frailty, and pain.

But that version of cannabis use wasn’t studied here. The person who takes a nightly 2.5mg gummy to wind down after their spouse’s passing? That person is invisible in this dataset.

We need more research, not more blanket warnings built on incomplete models.

🧬 A Note on Brain Health and Cannabis

Let’s not pretend cannabis has no effects on cognition. Of course it does—especially in high doses, and especially in younger users.

But cannabis’s interaction with the brain is dose-, route-, and context-dependent. The hippocampus may be sensitive to chronic THC, but it’s also deeply affected by depression, stroke, and chronic inflammation—conditions where cannabis might help, not harm.

The field of cannabis and neurodegeneration is in its infancy. This study doesn’t close the case. It barely opens it.

🧓 What This Means for Patients and Families who are worried about cannabis and dementia?

If someone you love has had a cannabis-related hospital visit, especially later in life, it may be a clinical cue to:

♦️ Check in on their cognitive baseline

♦️ Review medications and interactions

♦️ Discuss emotional health and substance use

♦️ Monitor changes over time with compassion, not judgment

But it doesn’t mean they’re doomed to dementia. It means they had an acute episode. The rest of their story still matters.

Likewise, if you’re using cannabis in low doses under medical guidance, this study probably has very little to do with you. But it’s a good reminder to:

• Talk with your doctor (the real kind—not the dispensary budtender)

• Keep track of your cognition

• Stay informed, but don’t buy into headlines without context

🎯 Final Thoughts

Studies like this are important. They shine a light. But they can also cast shadows—especially when the data is narrow, the framing is alarmist, and the conclusions are overstated.

Dementia is scary enough without weaponizing half-truths. Let’s keep asking better questions—and demanding better answers.

Want to understand how cannabis actually fits into healthy aging?

Start here.

🔗 External Link:

Read the full study 

🔗 Suggested Internal Links:

Cannabis for Seniors: What You Should Know

Is Cannabis Addictive? A Doctor Explains

The Cannabis Anxiety Survival Guide