THCA vs THC: what the difference really is

What is THCA?

THCA stands for tetrahydrocannabinolic acid (the full name is delta-9-tetrahydrocannabinolic acid). It's the form of THC the cannabis plant builds, starting from another acid called CBGA. Chemically it's THC with an extra carboxyl group attached, a small cluster of carbon, oxygen and hydrogen that makes the molecule a bit heavier.

That extra piece matters. THCA on its own isn't considered intoxicating, and research suggests the body converts very little of it into THC when it's eaten raw. The high people associate with cannabis comes from THC, which shows up once THCA has been heated.

How does THCA turn into THC?

The change is called decarboxylation, or "decarbing". Heat knocks the carboxyl group off THCA, it leaves as carbon dioxide, and what's left behind is THC. Lighting a joint, using a vaporizer or baking cannabis into butter all do this. It happens fast under heat but isn't perfectly complete, which is why some THCA is still detectable in people after they consume cannabis.

A 2016 study measured how quickly this happens by heating cannabis extracts in a vacuum oven. Below 100°C, THCA didn't fully convert even after an hour. At 110°C it was essentially gone in about 30 minutes, at 130°C in about 9 minutes and at 145°C in about 6. THCA converted cleanly, with only a small loss (around 8% at 110°C). Those were careful lab conditions, not a kitchen or a lighter, so read the numbers as a picture of the chemistry rather than a recipe.

Time does the same job, just slowly. THCA gradually turns into THC as flower dries and sits in storage, and THC itself slowly breaks down into another cannabinoid called CBN.

Why is raw cannabis flower mostly THCA?

Because that's what the plant makes. Cannabis produces its cannabinoids in their acid forms: THCA, CBDA and CBGA. The neutral versions, THC, CBD and CBG, aren't present in significant amounts in the fresh plant. They appear mainly once heat or light gets involved.

So when a lab tests a jar of dried flower, the THCA number is usually big and the plain THC number is small. That doesn't mean the flower is weak. It means most of its THC is still waiting for heat. This is exactly the gap the "Total THC" figure on Canadian labels is designed to close.

How is Total THC calculated on Canadian labels?

In Canada, the Cannabis Regulations require legal products to state their THC content as Total THC. The regulations define this as THC that takes into account the "potential to convert THCA into THC", meaning the most THC you'd get if all the THCA converted, with no further breakdown of the THC.

In practice, labs work it out with this formula:

• Total THC = THC + (0.877 × THCA)

The 0.877 comes straight from the chemistry. When THCA loses its carboxyl group, it loses about 12% of its weight: THC weighs about 314 grams per mole and THCA about 358, and 314 divided by 358 is roughly 0.877. So 100 mg of THCA can become at most about 88 mg of THC. The regulations describe the principle rather than printing the number, but the number is simply what that principle works out to.

Here's a worked example. Say a batch of flower tests at 10 mg/g THC and 220 mg/g THCA. Multiply 220 by 0.877 to get about 193, then add the 10: the label would show about Total THC 203 mg/g. That's roughly 20%, if you're used to thinking in percent.

A 2025 amendment to the regulations removed the old requirement to also print plain THC and CBD numbers, so current Canadian labels must show Total THC and Total CBD. Older packaging may still show both. For everything else on the package, see our guide to reading cannabis labels.

What is THCA flower, and is it a thing in Canada?

"THCA flower" is a US phenomenon, and it comes from how American law defined hemp. The 2018 Farm Bill said hemp was cannabis with no more than 0.3% delta-9 THC on a dry weight basis. THCA wasn't counted toward that limit, so flower that was very high in THCA but low in plain THC could be sold as hemp, even though heat turns it into THC like any other cannabis. That gap is often called the "farm bill loophole".

It's closing. A US federal law passed in November 2025 (Public Law 119-37) rewrites the definition so the 0.3% limit applies to total THC, including THCA. According to the US Congressional Research Service, the change takes effect on November 12, 2026. State rules vary on top of that.

Canada never had that gap. The Industrial Hemp Regulations set a limit of 0.3% THC in hemp's flowering heads and leaves, and they say that measurement must take into account the potential for THCA to convert into THC. In the legal cannabis market, THCA is folded into the Total THC number on every label. So in Canada, "THCA flower" isn't a separate product category. It's just cannabis flower, regulated like any other.

How to read THC and THCA numbers

On a Canadian label, Total THC is the number to use. It already includes the THCA, so you don't need to do any math, and it lets you compare one product with another on the same footing. If you see a certificate of analysis or an older package that lists THC and THCA separately, run them through the formula above before comparing.

Remember that Total THC is a ceiling, not a guarantee. Conversion is never perfect, some THC is lost along the way, and how much reaches you depends on how you consume it. Two products with the same number can also feel different to different people, and a high THC figure on its own doesn't tell you much about the experience. Terpenes like myrcene and limonene get a lot of attention for that reason, though the science on how much they change things is still unsettled. And if you've heard that type labels predict the high, our indica vs sativa guide explains why that's shakier than it sounds.