Cannabidiol (CBD) oil is essentially a concentrated solvent extract made from cannabis flowers or leaves that is dissolved in an edible oil such as sunflower, hemp, or olive oil. Solvents used can vary from relatively innocuous organic solvents (ethanol, isopropyl alcohol) to more harmful ones (petroleum-ether, naphtha), or even supercritical fluids (butane, CO2). The exact conditions and solvents applied have a great impact on, for example, the taste, color, and viscosity of the final product. Because many other plant components are co-extracted with the desired cannabinoids present in the herbal material, these are sometimes removed by a treatment known as “winterization.” By placing the extract in a freezer (–20 to –80°C) for 24–48 h, components with a higher melting point such as waxes and triglycerides, as well as chlorophyll will precipitate, so they can be removed by filtration or centrifugation . This treatment can significantly improve the taste and color of the final product.
Cannabis oils may contain various concentrations of CBD, tetrahydrocannabinol (THC), and minor cannabinoids, mainly depending on the cannabis variety used for extraction. The most popular product currently is CBD oil, but for example cannabigerol (CBG)-rich oil has been spotted as well , and others will very likely follow soon. The THC-rich type of cannabis oil has already been known for some years, and is generally known under the name “Simpson oil” . Terpenes may or may not be present in these products, depending on the preparation method used . Because they are highly volatile, elevated temperatures (such as those applied during drying of plant materials, or during the evaporation of solvents) may result in a significant loss of terpene components . However, it is possible to capture evaporated terpenes by condensation, and reintroduce them back into the final oil. Additional ingredients may be added to further adjust properties such as color, viscosity, taste, or shelf-life stability.
What Is CBD Oil
It is well known that cannabis plants obtained from uncontrolled sources may be contaminated with various harmful substances , sometimes leading to severe health issues or hospitalization . Contaminants include chemicals that were intentionally added in order to increase yield, weight, or potency (e.g., pesticides, metal particles , synthetic cannabinoids ) but also agents that entered the plant unintentionally (e.g., heavy metals, molds and bacteria , aflatoxins). For example, pesticides are frequently present in cannabis sold by Dutch coffee shops , but were also found in cannabis offered under state law in California  as well as medicinal cannabis from licensed producers in Canada . If any of these contaminants were present in hemp used for CBD extraction, they would likely end up in a concentrated form in the final oil. One contaminant specifically relevant to cannabis (CBD or THC) oils is the residual presence of toxic solvents used during the extraction procedure .
Recently, an interesting study performed in the Netherlands highlighted multiple issues that may be extrapolated to CBD products elsewhere . In this study, 46 different cannabis oil samples were collected directly from patients and analyzed for cannabinoid content. The obtained samples were home-made (n = 29) or purchased from a (web) store (n = 17). For 21 of the 46 products (46% of all samples), label information was available on CBD/THC content, so that the claimed content could be compared to the analyzed content as determined in the study. Results are shown in Table 1. In many cases the analyzed cannabinoid content strongly differed from the claimed content on the label, while in 7 samples no cannabinoids (CBD or THC) were found at all. Such deviations were found in home-made as well as commercially obtained products.
Another interesting observation was the presence of high levels of non-decarboxylated cannabinoids in multiple samples. It is well known that CBD and THC are not produced as such by the metabolism of the cannabis plant. Instead, cannabinoids are excreted in the form of carboxylic acids such as CBD-acid and THC-acid . The physiological effects of these “acidic” cannabinoids have been studied only to a very limited extent. Only after proper heating (e.g., during smoking, vaporizing, or baking with cannabis) are these natural precursors rapidly converted into the more well-known CBD and THC, respectively. This process is called decarboxylation . Although decarboxylation also takes place during the production of cannabis oils (e.g., during the evaporation of solvents, or during a separate decarboxylation step as part of the production process), 7/46 samples (15%) contained > 25% of its cannabinoid content in the form of acidic cannabinoids, indicating poor control over the decarboxylation process. To address the issue, some producers simply add up the content of CBD and CBD-acid in order to boast a higher “total CBD” content on the label, while advertising this as “raw CBD.”
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Potential Competing Interests: The authors report no competing interests.
Abbreviations and Acronyms
Cannabidiol (CBD) oils are low tetrahydrocannabinol products derived from Cannabis sativa that have become very popular over the past few years. Patients report relief for a variety of conditions, particularly pain, without the intoxicating adverse effects of medical marijuana. In June 2018, the first CBD-based drug, Epidiolex, was approved by the US Food and Drug Administration for treatment of rare, severe epilepsy, further putting the spotlight on CBD and hemp oils. There is a growing body of preclinical and clinical evidence to support use of CBD oils for many conditions, suggesting its potential role as another option for treating challenging chronic pain or opioid addiction. Care must be taken when directing patients toward CBD products because there is little regulation, and studies have found inaccurate labeling of CBD and tetrahydrocannabinol quantities. This article provides an overview of the scientific work on cannabinoids, CBD, and hemp oil and the distinction between marijuana, hemp, and the different components of CBD and hemp oil products. We summarize the current legal status of CBD and hemp oils in the United States and provide a guide to identifying higher-quality products so that clinicians can advise their patients on the safest and most evidence-based formulations. This review is based on a PubMed search using the terms CBD, cannabidiol, hemp oil, and medical marijuana. Articles were screened for relevance, and those with the most up-to-date information were selected for inclusion.
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