'Reefer Madness' era anti-marijuana campaigns often touted the deadly cannabis overdose—something that advocates have contested for a long time. Nowadays cannabis experts side with activists in dispelling the overdose myths.

First up in the case against the cannabis overdoses is the matter of numbers. There simply aren't any confirmed cases of cannabis overdose.

"As far as we can tell there have been no recorded cases of lethal amounts of cannabis ingestion resulting in overdose," Dr. Jeffery Chen, Director of the UCLA Cannabis Research Initiative told Mashable.

Some cannabis opponents might argue that once cannabis is normalized, people will begin to consume a lot more of it, leading to overdoses. But Chen says the lack of cannabis overdoes doesn't have anything to do with excess consumption. He says the reason why people overdose on things like alcohol and opioids and not cannabis is because those substances interact with different parts of the brain.

"The reason that these can result in overdoses is that these receptors tend to reside in the part of the brain that control breathing."

"If you can overstimulate those receptors when you take too much opioids, or drink too much alcohol, for example, you can actually shutdown the neurons in the part of your brain that controls breathing. And as soon as you stop breathing that's when you can have a lethal overdose."

Cannabis doesn't interact with the parts of the brain that regulate breathing and so probably isn't capable of triggering an overdose.

"With cannabis, the cannabinoid receptors that cannabis acts upon are not particularly abundant in the area of the brain that controls breathing. And so, for this reason ingesting a large amount of cannabis or cannabinoids—as far as we can tell—isn't going to shutdown your respiratory system."

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