The Cannabis plant does not produce THC (Delta-9-tetrahydrocannabinol) directly. Instead, it first produces a precursor to THC, called THC-A (tetrahydrocannabinolic acid). Decarboxylation is the chemical reaction responsible for the removal of the carboxylic acid group, converting the THCA into THC.

What is a carboxyl group

To keep it relatively simple without going too deep into the chemistry, it is a single Hydrogen and Carbon Atom with two Oxygen atoms that are all grouped together and bonded to the THC. Heat or time causing this bond to break is Decarboxylization.

Why break the bond

THCA is non-psychoactive, meaning it won’t get you high. The reason THC-A is non-psychoactive is that the THCA molecule is too large to fit into our brains’ cannabinoid receptors compared to a THC molecule due to the additional carboxyl group.

Now you may be thinking, “that doesn’t make sense, I smoke weed all the time and it gets me high. How does that work if there is only THCA and it is not non-psychoactive?”
Well, what happens when you smoke or vaporize cannabis is that you are applying heat to the THCA and decarbing it as you smoke it, breaking down the THCA into THC by destroying the carboxyl group with heat as you smoke it.

How to decarboxylate

Just set your oven to 122C or 252F and you’re set. Leave it for an hour or two and you will have decarboxylated your cannabis fully and it will be ready for edibles. You can put the cannabis in a sealed glass mason jar to reduce smell and keep some of the terpenes in. It’s also worth noting that THCA converts to THC at a rate of 87.7%, so 1 gram of THCA will convert to 0.877 gram of THC. This rate is used when calculating the percentage of THC in a product in stores. Most of the time there is not THC but THCA instead but they show the converted rate.

Can you overcook it and ruin the THC?

There is a lot of misinformation floating around the internet about decarboxylation. Some of it roots from one poorly done study that made this graph:

It leads many to believe that low temperature was needed and higher temperatures above 250F would nearly immediately destroy the THC content. However, this study was flawed as it was heated on an open glass surface exposed to air and oxidization as well as being extremely low thc content to begin with. As you can see there was less than 15mg of THC content per gram at the peak, for ‘hexane concentrate’ that is a very low THC per gram of less than 1.5%

A more modern study found more relevant information.

In the study, they dissolved 25 grams of Kief in 500ml of liquid coconut oil. Their solution sat for two months and before starting lab analysis which found the THCA solution was free from CBN. This gave a baseline of 0.00% CBN concentration.

The THCA solution was set on a Hotplate Stirrer, the probe temperature to 122°C and plate temperature to 350°C. Once the solution reached the set temperature the Multi-Timer automatically engaged the device for 24-hours.

Sample #1(6 Hour Collection) | THC to CBN Conversion: 0.1 mg/ml
Sample #2 (12 Hour Collection)| THC to CBN Conversion: 0.2 mg/ml
Sample #3 (18 Hour Collection)| THC to CBN Conversion: 0.3 mg/ml
Sample #4 (24 Hour Collection)| THC to CBN Conversion: 0.4 mg/ml

Samples were collected at 6 hour intervals and each sent to an independent laboratory for analysis. The experiment concluded that the rate of THC to CBN conversion is so low it is barely noticeable and not worth all the worry that people put into doing it for the exact proper time.
While the THC levels of the Kief were not disclosed in the study, we can assume 25 grams gives at least 2500mg of thc, and that’s at a very conservative estimate. 2500mg of THCA in 500ml is 50mg/ml, so even after 24 hours only 0.4mg/ml is converted, which means only 0.008% of the THC has degraded after 24 hours of 252F.

I hope this helps out your mind at ease when decarbing in the future. Good luck with making some great edibles!

Sources:

https://catscientific.com/decarboxylating-cannabis/
https://kundoc.com/pdf-determination-of-cannabinoid-acids-by-high-performance-liquid-chromatography-of-.html