Good Question

Can I Overdose on Cannabis?

What adverse reactions look like — and how risky they really are

Photo Illustration: Save As/Medium; Source: Olena Ruban/Getty Images

Welcome to my new column for Elemental. Each Tuesday, I’ll attempt to answer a thought-provoking health question with the help of one or two experts. If you’d like to suggest a topic, please email me at

Michigan voted to legalize recreational marijuana late in 2018. Open-to-the-public sales began a year later, but I didn’t partake until the fall of 2020, when the monotony of the pandemic and the prospect of a long, isolated winter made a little psychotropic dabbling seem like a good idea.

In Detroit, where I live, the sale of recreational cannabis is still outlawed. And so on a snowy Wednesday evening I drove to a nearby suburb and waited — first in a long line of cars, and then in a parking lot — for a masked dispensary worker to bring out my packet of indica gummies. I went home, cut each of the gummies into fifths, and ate one of these pieces. I felt what I expected to feel, which was a kind of mild cognitive reshuffling — as if someone had slightly rearranged the furniture in the living room of my mind — and an almost imperceptible body buzz.

Since then I’ve been eating a bit of gummy in the evening a few times a month. The break from my usual routine has been a pleasant one. I’m ingesting about 2 mgs of THC each time, which suits me. At this point in my life, it’s all I need or want. But the fact that such a small amount of THC has any effect at all makes me wonder what would happen if I ate or smoked significantly more. (While practices vary widely, many people prescribed cannabis for a medical condition start out taking somewhere between 2 and 10 mg of THC per dose.) I’ve always heard that you can’t overdose on marijuana, but I have no idea if that’s true. Hypothetically, what’s the worst thing that could happen if I overdid it?

“That depends critically on how much THC you consume,” says Wayne Hall, PhD, former director of the National Drug and Alcohol Research Centre at the University of New South Wales in Australia. Hall has researched cannabis for decades, and has published hundreds of peer-reviewed articles on the drug’s effects, good and bad.

THC is short for tetrahydrocannabinol, which is the principal psychoactive chemical in cannabis. “With legalization in the U.S., we’re seeing cannabis extracts with very, very high THC, and we’re seeing more people turn up in emergency departments with adverse reactions,” Hall explains. In adults, he says these adverse reactions include severe anxiety, paranoia, hallucinations, and other “psychotic” symptoms. A racing heart and, in rarer cases, nausea and vomiting are also well-documented phenomena. It’s hard to know exactly how common such reactions are nationwide. Some fairly recent data suggest that alcohol-related hospital admissions dwarf the number of cannabis-only hospital admissions by a factor of 25. But many, many more people consume alcohol, which makes such comparisons tricky.

There is evidence that some types of cannabis may be more likely than others to provoke a bad reaction. A 2019 study published in Annals of Internal Medicine looked at the characteristics of thousands of cannabis-related emergency department visits at a Colorado hospital between 2012 and 2016. It found that edible products, which at that time accounted for less than .5% of cannabis sales in Colorado, were associated with almost 11% of hospital visits.

Hall explains that when people smoke marijuana, the effects tend to be almost immediate and are therefore self-limiting. Some heavy and habitual smokers are able to tolerate so much THC that they can keep smoking to the point that they have a bad reaction. (Nausea and vomiting seem to be more common among regular users, as opposed to newbies or dabblers.) But with ingestible products, there’s often a lag between consumption and felt effect. “It’s easier for people to take a lot more than they intend to,” he says.

Hall and I spend some time talking about the risks of heavy and habitual cannabis use. Those are real and merit greater public discussion and awareness, especially when it comes to the way cannabis seems to affect the brains of young people. We also discuss the demonstrated and potential benefits of cannabis. But those are topics for another day, and I steer our conversation back to the worst possible outcomes of an acute cannabis overdose. Could I die or suffer any permanent damage?

Hall says there are some reports of stroke or heart events following an acute overdose. But these are vanishingly rare and may not be strictly attributable to cannabis. He also says that cannabis mixed with other drugs — and in particular, synthetic cannabinoid products such as Spice or K2, which are generally illegal — are a whole other animal. Research has linked these concoctions to heart attacks, seizures, and other life-threatening reactions. But when it comes to pure cannabis, including high-THC products, the risks of a deadly or damaging overdose seem to be “quite low,” he says.

Other experts agreed. “A fatal overdose after cannabis consumption is highly unlikely,” says Kevin Hill, MD, an associate professor of psychiatry at Beth Israel Deaconess Medical Center and Harvard Medical School. I ask him if it’s possible I could have lingering health issues following an acute overdose. “Not to my knowledge,” he says. “Effects of acute cannabis intoxication are transient.”

I don’t plan to put their assurances to the test.

I write about health and science. I live in Detroit with my wife and kids. I’m trying to learn German, but my progress so far is nicht gut.

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