#202 Cannabis Overdose: How Much Is Too Much?
#202 Cannabis Overdose: How Much Is Too Much?
Ask ten people whether you can overdose on cannabis and you will get two confident answers. One camp says it is impossible and nobody has ever died from it. The other says overdoses send people to hospital every day. Both are partly right, and the gap between them comes down to what the word "overdose" means. Here is what the research shows, what greening out actually is, and when a bad night needs a doctor.
What "overdose" means
In everyday speech, an overdose means a dose that can kill you. In medicine, it means any amount large enough to cause harm, fatal or not. Someone who takes too much of a cold medicine and spends the night vomiting has overdosed, even though they were never in danger of dying.
By the first meaning, cannabis is one of the safest substances people use. By the second, overdoses happen all the time. Keeping those two ideas apart clears up most of the confusion.
Is there a lethal dose?
Toxicologists rate how dangerous a substance is by comparing the amount that produces an effect with the amount that would kill half of the animals given it in a lab. That second figure is called the LD50. The wider the gap between the two, the safer the substance.
For alcohol, the gap is narrow. Roughly ten times a normal drinking dose can be fatal, which is why alcohol poisoning kills people every year. For cannabis, the gap is so wide that it has never been pinned down in people.
Writing in American Scientist in 2006, psychologist Robert Gable estimated that eaten cannabis would take somewhere between 100 and 1,000 times the effective dose to cause death, and added that he could find no published case of anyone dying from smoked cannabis. A 1988 ruling by a US Drug Enforcement Administration judge put it more vividly: a person would need to smoke close to 680 kilograms of cannabis in about fifteen minutes.
The reason is biological. The drugs most likely to cause a fatal overdose, such as opioids and alcohol, slow down the part of the brain that keeps you breathing. That area has very few of the receptors THC acts on, so even a huge dose does not switch off breathing the way a large dose of fentanyl can.
A 2020 review of every cannabis-related death reported to Australian coroners between 2000 and 2018, 559 cases in all, found that none was caused by cannabis poisoning alone. The deaths came from car crashes and other accidents, from suicide, from heart and lung disease, and from mixing cannabis with other drugs, most often alcohol.
Greening out
Greening out is the common name for taking more THC than your body can handle. It is not life-threatening for most healthy adults, but it can be miserable and frightening. Typical signs include:
● A racing heart and a sense of panic or dread
● Nausea, vomiting and sweating
● Dizziness or feeling faint, especially when standing up quickly
● Confusion, paranoia, or feeling detached from your surroundings
● Shaking or feeling very cold
The panic often feeds itself. A fast heartbeat feels like a heart attack, the fear pushes the heart rate higher, and the cycle repeats. Knowing that this is a normal reaction to too much THC, and that it will pass, often helps more than anything else.
Smoked or vaporized cannabis usually peaks within half an hour and fades over a few hours. Edibles are a different story. They can take up to two hours to start working, peak several hours later, and last well into the next day. The most common way to green out is to eat a gummy, feel nothing after 45 minutes, and take a second one.
Why emergency room visits are rising
If cannabis rarely kills, why are hospital visits climbing? Canadian data points mostly to two groups.
The first is young children. A 2022 study found that emergency visits for cannabis poisoning in Ontario children under 10 rose roughly ninefold after legal edibles went on sale in 2020. The average child was under four years old, and about a third of visits ended in a hospital stay. A small child who eats an adult's gummy is getting a far larger dose for their body weight, and in children the effects can include extreme drowsiness, trouble breathing and seizures. This is the one group where a cannabis overdose can become a true medical emergency.
The second group is long-term, heavy users. A condition called cannabis hyperemesis syndrome causes repeated bouts of severe vomiting and stomach pain in some people who use large amounts daily for months or years. A second study by the same Ottawa team found that emergency visits for the condition in Ontario rose thirteenfold over seven and a half years. It is not an overdose in the usual sense, and the only lasting fix is to stop using.
Beyond those two groups, most adult visits involve panic, fainting and falls, mixing cannabis with alcohol, or people with existing heart problems.
When to get medical help
Most adults who green out need water, a quiet room and time. Call 911 or go to an emergency department if someone:
● Has chest pain or an irregular heartbeat, especially with a history of heart problems
● Faints, cannot stay awake, or has a seizure
● Cannot stop vomiting or cannot keep fluids down
● Has taken cannabis together with alcohol or other drugs
● Shows signs of losing touch with reality, such as hearing voices
● Is a child or a pet who may have eaten cannabis
For questions that are not emergencies, Canada's poison centres can be reached around the clock at 1-844-POISON-X (1-844-764-7669).
Avoiding it in the first place
Start with a low dose, especially with edibles, where 2.5 mg of THC is a sensible first step for a new user. Wait at least two hours before taking more. Avoid drinking alcohol at the same time, since the two together make greening out far more likely. Store every cannabis product in its child-resistant package, up high and out of sight, as you would any medication.
Stay cannabis-smart
You cannot take enough cannabis to stop your own breathing, and no reliable record shows anyone has died from THC poisoning alone. You can take enough to spend a long, unpleasant night on the bathroom floor, and a child who finds your gummies can end up in intensive care. Respect the dose, wait on edibles, and lock them away.
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