Cannabis consumers who are receiving their cannabis orders from a provincial retail outlet, such as the Ontario Cannabis Store, may find listed on the label “Total THC” as a percentage, likely a foreign concept for most.
Total THC often refers to the total potential amount of tetrahydrocannabinol, or THC—the chemical responsible for most of marijuana’s psychological effects—in the cannabis after it has been heated.
Cannabis often contains a small percentage of THC before being heated, which may be indicated on the label as a percentage. What may not be known is that cannabis does not have a high percentage of THC before being heated. Instead, it has a cannabinoid called tetrahydrocannabinolic acid, or THCA, the non-psychoactive compound that gets converted to THC after it is heated and as well as when the plant dries.
The extra molecule is key
THCA is basically THC except with an extra CO2 (carbon dioxide) molecule added. THCA’s molecular formula is C22H30O4, and THC’s is C21H30O2. Here C represents carbon, H is hydrogen and O is oxygen.
Notice how THCA’s formula has one more carbon, at 22, and two more oxygen, at four, than THC’s formula. This makes up the extra CO2 in THCA.
When heat is applied to THCA, it losses that CO2 and becomes THC through a process called decarboxylation—which makes sense, given that it is losing a carbon dioxide.
Since THC does not have the extra CO2 that THCA has, it has a smaller molecular weight. THCA has been found to have a molecular weight of 358.48 compared to THC’s 314.47. This is why Total THC is not simply THCA plus the THC in the plant before heating it, but, rather, is a fraction of THCA.
What happens when heat is applied?
Heating cannabis at 200 C for a few seconds results in 100 percent decarboxylation
When THC’s molecular weight is divided by that of THCA’s, the result is 0.877. In a perfect world, if THCA was heated, 87.7 percent of it would be converted to THC.
However, THCA is often not fully converted to THC when heated. It depends on the temperature at which it is heated, since at very high temperatures, some THC may be degraded to cannabinol, or CBN, which is known to treat pain relief and has a sedative effect, but has no intoxicating effects.
Heating cannabis at 200 C for a few seconds results in 100 percent decarboxylation of THCA to THC, without forming CBN, notes information from the European Industrial Hemp Association. While this exact temperature can be achieved through vaporizing, the temperature of a standard lighter is well over 1,000 C. That means THC can be expected to degrade into CBN if cannabis is heated this way.
Regardless of the potential for there not to be 87.7 percent THC from the original amount of THCA, cannabis labels still assume there is full conversion in their Total THC figure.
As such, Total THC is accurately determined by multiplying the amount of THCA by 0.877, and then adding the original amount of active THC in the cannabis that was there before being heated. Specifically, the formula for Total THC is (0.877xTCHA) + THC.
Source: 420 Intel
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