Conversion of CBD to THC

Cannabidiol (CBD) can be chemically converted into tetrahydrocannabinol (THC) via a ring-closing reaction. This cyclization can be acid-catalyzed or brought about by heating.

Known methods
Plant cannabinoids exist like precursors to their pharmacologically active counterparts. At least three independent methods have successfully converted CBD to THC.


 * Despite the CBD and THC having the same molecular weight, multiple analytical methods are able to differentiate them.
 * "on the recovery of both THC (86.7−90.0%) and CBD (92.3−95.6%). The slightly lower recovery of THC can be explained by the fact that THC is less polar than CBD and more likely to remain in the nonpolar sunflower oil."

By heat
CBD heated to 175, or 250–300 °C may partially be converted into THC. Even at room temperature, trace amounts of THC can be formed as a contaminant in CBD stored for long periods in the presence of moisture and carbon dioxide in the air, with storage under inert gas required to maintain analytically pure CBD.


 * Heat is required to decarboxylate THCA to psychoactive cannabinoid THC. Likewise, CBDA turns into CBD.
 * From hemp plant material in an oven, cannabinoid concentration plots (time/temp) show THC:
 * STP 0 minutes 0.20mg/g
 * 140-160C 20 minutes 0.27mg/g
 * 140-160C 60 minutes 0.05-0.15mg/g
 * 120C 45 minutes 0.27mg/g
 * 120C 90 minutes 0.20mg/g
 * 100C 90 minutes 0.25mg/g
 * 80C 120 minutes 0.24mg/g

Multiple oxidation products begin to form with degradation (the loss is greatly reduced in the absence of oxygen).


 * "...the boiling point for THC has been determined at 157 °C, and the boiling point range for CBD sits between 160 and 180 °C."

With acid


CBD converts to various isomers of THC with catalysts in acidic environments. A wide variety of acids can be used, though different conditions result in varying yield and formation of characteristic impurities.


 * Adding protons until the CBD sterically-hindered alcohol functional group cyclises to the pyran ring of THC.
 * Lewis acids. - a continuous rather than batch implementation with similar materials
 * Catalytic acid solution in 5 minutes in a microwave with a 40% Δ9 and 35% Δ8 yield
 * (−)-Δ8-THC, which can be converted to trans-(−)-Δ9-THC by addition of HCl followed by dehydrochlorination
 * Treatment of the purified Δ8 -THC with hydrogen chloride in the presence of zinc chloride gives the chloro compound which is isolated and subsequently treated with potassium tert-amylate to yield the desired (-)-6a,10 a-trans-Δ9 -tetrahydrocannabinol. The Mechoulam and Petrzilka methods require three steps and involve at least two careful chromatographic separations to obtain (-)-6a,10 a-trans-Δ9 -tetrahydrocannabinol of high purity.
 * Gaoni and Mechoulam also described a method for converting CBD to Δ9-THC comprising boiling a mixture of CBD in ethanol containing 0.05% hydrogen chloride for 2 hours. Percentage yield of Δ9-THC (Δ1-THC) was 2%. Using boron trifluoride, the yield was 70% although purity was not given.

With zeolite
Methods have been claimed for converting CBD to a mixture of Δ8-THC and Δ9-THC using "Zeolites selected from the group consisting of analcime, chabazite, clinoptilolite, erionite, mordenite, phillipsite, and ferrierite."

In vivo
There is a debated hypothesis that oral CBD could be converted into THC under acidic conditions in the stomach and then absorbed into the blood stream. However, neither THC nor any of its active metabolites have been detected in blood in animals or humans after ingesting CBD. There is no direct evidence of the conversion of CBD to THC in the human gut; both CBD and THC are excreted unchanged within human feces.