Dear Herb: My legal cannabis lists two different numbers for THC. Why?

Herb explores the difference between "THC" and "Total THC" on cannabis packaging in Canada


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Dear Herb: I bought some legal weed the other day, and on the bottle it says, "THC 0.27 per cent." Next to that, it says, "Total THC 16.9 per cent." What does this mean? — Multiple Choice

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Hey there, time traveller!
This article was published 02/01/2019 (1492 days ago), so information in it may no longer be current.

Dear Herb: I bought some legal weed the other day, and on the bottle it says, “THC 0.27 per cent.” Next to that, it says, “Total THC 16.9 per cent.” What does this mean? — Multiple Choice

Dear Multiple Choice: Excellent question. I suspect this is confusing to lots of cannabis consumers in Canada these days.

If you’re at all familiar with cannabis, you know that THC — tetrahydrocannabinol — is a cannabinoid, one of the key chemical compounds produced by cannabis that causes a psychoactive effect when ingested. The proportion of THC in cannabis is generally considered a rough measurement of the potency of the cannabis. (In reality, other factors such as terpenes also play important roles in how cannabis affects human physiology, but let’s leave that aside for now).

A package of legal cannabis. (Mike Deal / Winnipeg Free Press files)

However, cannabis plants don’t actually produce THC; instead, fresh cannabis buds contain THCA (tetrahydrocannabinolic acid), which is a non-psychoactive substance — it won’t get you high. When that cannabis is heated sufficiently, the THCA is converted to THC by way of a chemical process called decarboxylation.

So the initial, smaller number on your cannabis package represents the relatively small amount of THC that’s actually contained in the packaged cannabis before it’s heated up. The second, larger number represents how much THC that cannabis should actually yield when it’s smoked, vaporized or otherwise decarboxylated (during cooking, for example).

Therefore, the cannabis you bought contains 0.27 per cent THC by weight in its raw form. Before decarboxylation, a gram of that cannabis ought to contain a modest 2.7 milligrams of THC.

But if you rolled that entire gram of cannabis into a big ol’ joint and smoked it, it would yield THC equal to 16.9 per cent of its weight, or 169 milligrams of THC. Not all of that THC would make its way into your lungs, though — a good deal of it would get lost in the process of burning the cannabis.

“You’re probably only getting half or less of that when you’re actually ingesting it through smoking, through combustion,” says Alexzander Samuelsson, lead chemist with cannabis processing and technology firm Nextleaf Solutions.

“That (fire) is actually destroying molecules as it’s going through the joint, but you’re also holding it and it’s literally evaporating the THC into the air.”

At this point, you might be wondering: since cannabis plants produce THCA instead of THC, why is there any THC at all in your unheated cannabis? The answer is that the weed you bought isn’t fresh off the plant. It’s been dried and cured, a process that slowly decarboxylates a small proportion of THCA and turns it into THC.

Here’s the bottom line: From a cannabis user’s perspective, the smaller THC figure on legal cannabis packaging can be ignored in favour of the larger “Total THC” figure.

“The total potential (THC) is what you’re really looking for to gauge your experience,” advises Samuelsson.

The first figure on this label shows THC by weight before the cannabis is heated up. The second, larger figure represents the actual THC yield of the cannabis after a chemical process called decarboxylation. (Mike Deal/Winnipeg Free Press.)

Finally, note that legal cannabis packaging in Canada treats CBD the same way. Under government regulations, producers have to label their cannabis with the actual amount of CBD and the total CBD after decarboxylation. Again, the larger “Total CBD” number is the one that matters to consumers.

Got a question about cannabis? Herb answers your questions about legal consumption and growing, the law, etiquette — you name it, he’ll look into it.

First, please check this list of questions already answered by Herb. Then, email, or to submit anonymously, fill out the form below. Please include an email address if you’d like to be notified when Herb answers your question:  


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