Cannabidiol Regulatory Difficulties
Cannabidiol has been known to induce several pharmacological effects. CBD is approved as a medicinal product subject to prescription. However, regulatory difficulties arise from its origin being a narcotic plant or its status as an unapproved novel food ingredient.
Cannabis sativa L. naturally contains several different cannabinoids that are related to the elementary structure of cannabinol (CBN). The most prominent representative among the class of these compounds is Δ9-tetrahydrocannabinol (Δ9-THC). Due to the well-known psychotropic properties of Δ9-THC, only the cultivation of plant varieties with low THC contents is authorized in the European Union (EU). 
There is a discrepancy in terms of the legality of products derived from the hemp plant. Cannabis products have been listed in the United Nations (UN) single convention on narcotic drugs from 1961 and are therefore prohibited regardless of their Δ9-THC content. However, processed products, if the Δ9-THC content does not exceed certain levels and abuse as a narcotic drug can be ruled out. 
As explicitly excluded by the definition of cannabis in the UN single convention, seed products (e.g., hemp seed oil), without the cannabinoid-rich resin, are generally regarded as safe and may be marketed in the EU. 
Pharmacological experiments with mixtures and/or single cannabinoids can be traced back to the 1940s and 1950s, when some studies regarding THC, CBN and CBD were published although structures were only elucidated in the mid-1960s. The known psychotropic effects of cannabis were mainly attributed to Δ9-THC consequently to substantial research during the mid-1960s and early 1970s. 
In 1971, the UN released a convention listing psychotropic substances in four schedules ranging from Schedule I (most restrictive), including five Δ9-THC derivatives, to Schedule IV (least restrictive). While Δ9-THC is listed in Schedule II (controlled). 
A controversial topic discussed in the recent scientific literature, is the potential conversion of CBD into psychotropic cannabinoids. 
To better understand the pitfalls of cannabinoid research with controversial results, we may need to explain some major analytical challenges: studies reporting conversion of CBD under acidic conditions and invitro conditions (using artificial or simulated gastric juice).
The current debate is about whether results of invivo studies in animal may be transferred to invivo conditions in humans. Finally, the debate about the conversion is expanded by the question of whether CBD converts to other potentially psychotropic cannabinoids under storage conditions. 
Despite the various problems arising from analytical challenges in the field of cannabis research, only 2% of all publications on cannabis deal with analytics. 
From their first detection, cannabinoids were mainly analysed by colour reactions, some of these tests were highly sensitive and enabled the proper differentiation. Besides that, thin layer chromatography (TLC), photometric and spectroscopicmethods were used as well. 
The development of gas chromatography (GC) in the early 1950s very soon reached the field of cannabis research.
The most important drawback of GC is due to high temperatures in the injector port and the column oven, acidic forms of cannabinoids are decarboxylated and are thus not detected in the resulting chromatogram. While this causes an underestimation of such compounds, it may also lead to a substantial overestimation of the decarboxylated active forms. 
Like GC, the invention of the high-performance liquid chromatography (HPLC) technique in the late 1960s quite immediately paved its way to the field of cannabis research. First reports on the use of HPLC started in 1975.
As multiple cannabinoids (e.g., Δ9-THC, CBD, and CBC) are isobaric isomers, they form identical signals and massspectra even with LC-MS/MS measurements. Hence, chromatographic methods with high separation performance are required for an unambiguous
peak assignment and avoidance of false positive results. 
Conversion of cannabidiol under acidic conditions
The acid-catalyzed conversion of CBD has been studied since the early 1940s. There are reports of the treatment of CBD with various acids and the conversion product was described to be a psychotropic cannabinoid, which the authors assumed to be either Δ9-THC or Δ8-THC. 
Later in 1966 other experiments described the correct structures of CBD, Δ9-THC and Δ8-THC based on careful spectroscopic studies (i.e., UV, IR, and NMR). Researchers were further able to verify the above-mentioned hypothesis that Δ9-THC was the main product if CBD was subjected to treatment with hydrochloric acid (HCl). The addition of p-toluenesulfonic acid, though, rather resulted in the formation of Δ8-THC. 
Conversion of CBD invitro conditions
In sight of the reported results, some may wonder if similar acid-catalyzed reactions are also possible in the acidic conditions of (artificial) gastric juice. The first report on the biotransformation of CBD to a derivative of the psychotropic Δ9-THC was presented in 1993. In their experiments, the authors incubated a CBD solution with hepatic microsomes of guinea pigs, rats, and mice, extracted the mixture, analyzed with GC/MS, and identified 6β-hydroxymethyl-Δ9-THC. 
More recently, studies investigated conversion products of CBD, which were formed upon subjection with simulated gastric juice and a physiological buffer solution.
Based on UPLC/UV and UPLC-MS/MS analyses, Δ9-THC and Δ8-THC were detected in simulated gastric juice and buffer after one to three hours of incubation. This led the authors to the conclusion that relevant levels of Δ9-THC and Δ8-THC may be formed in humans after oral consumption of CBD. 
In opposition to the above study, some researchers reported no observation of the formation of THC when CBD was incubated with artificial gastric juice or even stored under stress factors such as heat or light under moderate conditions. This study attached great importance to the physiological study design, especially about incubation times, temperatures during incubation and concentrations of solvents and analytes. 
Conversion of CBD invivo conditions
Even though the metabolism of CBD was studied in several animal species, in the early 1990s two researchers were the first to report on the human CBD metabolism. [15,16]
As they measured human urine samples with a GC/MS method after CBD was orally administered to, they found over 30 metabolites. Interestingly, they also reported the detection of two cyclized cannabinoids, which they termed “delta-6-THC” and “delta-1-THC” (the latter one most likely corresponds to Δ9-THC as termed by present nomenclature). 
They concluded that these analytes rather emerged artifactually in the urine sample than being metabolites formed in humans, as this would have caused visible “psychoactivity with obvious adverse effects for the patient”. 
This hypothesis was supported by the results of 14 patients with Huntington’s disease treated with a dose of CBD of 10 mg/kg/day and by the comparison of plasma levels of CBD with a group treated with a placebo. Over the course of six weeks, Δ9-THC was never detected in the plasma. 
Similar results were also reported while conducting a double-blinded study with16 healthy volunteers treated with either Δ9-THC (10 mg), CBD (600 mg) or a placebo. Nor were other psychotropic cannabinoids detected in insignificant quantities in the blood of patients treated with CBD, while the oral administration of Δ9-THC itself had both effects on the plasma concentration and measurable psychotropic potential. 
Conversion of cannabidiol during the storage
In a recent publication, after some consumer complaints noticing “THC-like effects” after taking CBD products, scholars listed multiple CBD products, which contained significant amounts of Δ9-THC and were thus reported in the Rapid Alert System for Food and Feed (RASFF) of the EU. 
The authors discussed three hypotheses for this effect:
- CBD may have a psychotropic action itself; this idea was immediately ruled out due to missing scientific evidence that CBD exhibits psychotropic effects;
- The transformation of CBD to Δ9-THC under invivo conditions; even though the authors rather neglected that option due to the results of their own conversion studies;
- Δ9-THC may already be present in the CBD products as contamination. 
A further hypothesis is that other psychotropic cannabinoids are not present in the original CBD extract or CBD product, but potentially result from reactions under storage conditions. 
The mechanism of the main decomposition route for Δ9-THC ultimately leads to the formation of CBN.  This was proven when researchers found low levels of Δ9-THC but increased levels of CBN in marihuana samples stored for nearly 100 years. 
Another long-term study reported on the decomposition of Δ9-THC but also CBD to the final product CBN in samples stored for four years in different conditions. As the decay of CBD was half the difference between the decay of Δ9-THC and the formation of CBN, the authors postulated the degradation route of CBD to start with a cyclization to Δ9-THC, which is followed by the decomposition to CBN.
Notably, room temperature and daylight were found to increase the decomposition rates in the studies. [22, 23] A recent report also highlighted the role of oxygen in the decomposition process, as samples stored in contact with air showed higher decomposition rates of Δ9-THC and CBD both in daylight and dark conditions. 
Hence, considering the effects of acidic conditions, decomposition processes and their dependence on temperature, it is necessary to consider exposure to light and oxygen when storing CBD products, to keep their composition intact and make consumers feel safe not to incur adverse effects.
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