Origin of Δ⁹-Tetrahydrocannabinol Impurity in Synthetic Cannabidiol

Introduction: Cannabidiol (CBD), the nonintoxicating constituent of cannabis, is largely employed for pharmaceutical and cosmetic purposes. CBD can be extracted from the plant or chemically synthesized. Impurities of psychotropic cannabinoids Δ⁹-tetrahydrocannabinol (Δ⁹-THC) and Δ⁸-THC have been found in extracted CBD, thus hypothesizing a possible contamination from the plant. Materials and Methods: In this study, synthetic and extracted CBD samples were analyzed by ultrahigh-performance liquid chromatography coupled to high-resolution mass spectrometry and the parameters that can be responsible of the conversion of CBD into THC were evaluated by an accelerated stability test. Results: In synthetic and extracted CBD no trace of THC species was detected. In contrast, CBD samples stored in the dark at room temperature on the benchtop for 3 months showed the presence of such impurities. Experiments carried out under inert atmosphere in the absence of humidity or carbon dioxide led to no trace of THC over time even at high temperature. Conclusions: The results suggested that the copresence of carbon dioxide and water from the air could be the key for creating the acidic environment responsible for the cyclization of CBD. These findings suggest that it might be appropriate to review the storage conditions indicated on the label of commercially available CBD.