[NOTE: In September 2020, ConsumerLab.com published its second Review of CBD and Hemp Extracts, providing tests, comparisons, and reviews of popular CBD-containing supplements, such as oils, capsules and gummies for people and pets, as well as balms and lotions, and updated information about CBD. CL has also tested hempseed oils as part of its review of seed oil supplements as sources of omega-3 and omega-6 fatty acids.]
Cannabidiol (CBD) is a compound derived from cannabis (a hemp plant also known as marijuana). However, unlike other compounds found in cannabis, such as THC, cannabidiol is not believed to be a psychoactive compound affecting perception, and behavior. Preliminary evidence suggests CBD may modestly reduce anxiety, certain measures of dystonia (a movement disorder), and glaucoma (Health Canada 2013).
A placebo-controlled clinical trial found a high daily dose of CBD (20 mg per kg of body weight, i.e., hundreds of milligrams) to reduce the frequency of convulsions in a rare form of epilepsy known as Dravet syndrome in children and young adults, although it was also associated with a higher rate of adverse effects including diarrhea, vomiting, fatigue, pyrexia, somnolence, and abnormal results on liver-function tests (Devinsky, New Eng J Med 2017). Similarly, the same high daily dose reduced the number of drop seizures among people with treatment-resistant Lennox-Gastaut syndrome in a 3-month study. Seizures per month decreased 44% with CBD compared to 22% with placebo; however, again, those taking CBD also had a higher rate of adverse effects including diarrhea, somnolence, fever, decreased appetite, and vomiting (Thiele, Lancet 2018).
A study of high-dose CBD (1,000 mg per day) among adults with schizophrenia found that adding CBD rather than placebo to existing treatments for six weeks reduced psychotic symptoms and caused a trend, although not statistically significant, toward improved performance on cognitive tasks. In this study, CBD was given in two divided doses (morning and evening) and was well tolerated with no increase in adverse effects (McGuire, Am J Psy 2017).
Although CBD is not psychoactive, it is not permitted to be sold an ingredient in dietary supplements, as the FDA considers it an investigational new drug. (Note: If an ingredient is marketed as a supplement prior to the FDA authorizing its investigation as a drug, it may continue to be marketed as a supplement, but this was not the case with CBD, according to the FDA). Two conditions for which CBD has been or is being investigated as a new drug are cancer pain and, as noted above, Dravet syndrome (view a list here of completed, ongoing, and planned studies with cannabidiol). In Canada, cannabidiol is a controlled substance.
Despite the fact that CBD cannot be legally sold in the U.S. as a dietary supplement, many CBD products are available. These include oils and capsules sold as supplements and CBC waters sold as foods. In February 2016, the U.S. FDA issued warning letters to eight companies selling products containing cannabidiol. The FDA also published the amounts of CBD, THC and other cannabis compounds it found in these products and those tested in 2015 (click here and select the year to view). Many products did not contain the levels of CBD they claimed. The FDA cautions that "Consumers should beware purchasing and using any such products." Most products contained very small concentrations of CBD — similar to what is normally found in hemp oil (about 0.0025% CBD) while others contained very large concentrations (25% to 35% CBD) yielding doses similar to those used in clinical trials (typically 200 mg or more per day).
The reason why hemp oils would not be expected to contain much CBD is that hemp oil is typically made from hemp seeds (i.e., hempseed oil), which contain little CBD. CBD is not found within in the seed (although some may contaminate the surface); it is principally found in the flowers and, to a lesser extent, the upper leaves of the hemp plant. A "CBD oil" product is typically an oil, such as from hemp seed or other sources, to which a CBD extract (from hemp flowers) has been added (Mead, Epilepsy & Behavior 2017). [NOTE: In September 2020, ConsumerLab.com published its Review of CBD and Hemp Extracts, providing tests, comparisons, and reviews of popular CBD-containing supplements, such as oils, capsules, and gummies for people and pets, as well as balms and lotions, and updated information about CBD. CL also tested hempseed oils as part of its review of seed oil supplements as sources of omega-3 and omega-6 fatty acids.]
At least one seller of CBD supplements to the public, PlusCBD LTD, appears to claim that is not illegal to sell these products if they are derived from "industrial" or "agricultural" hemp. Industrial hemp is typically a larger plant with more stalk and less leaves and flowers than that used to produce marijuana or CBD for medical use. It is grown for its fiber (for textiles) and seeds (as food and oil), which would be very low in THC (less than 0.3%) and CBD. It is true that the U.S. Drug Enforcement Agency (DEA) has stated that CBD in trace amounts from cannabis stalk or seeds is not a controlled substance, in contrast to CBD derived from cannabis flower which is a controlled substance -- despite the compound being the same. However, this does not seem to override the FDA's position that CBD cannot be sold as dietary supplement. It would also seem difficult to obtain large quantities of CBD from industrial hemp or cannabis stalk.
Many states now have medical marijuana laws that permit products with high CBD content to be sold by approved dispensaries and used by residents for medical purposes recommended by a healthcare provider. In addition, several states without medical marijuana laws allow products that are high in CBD (e.g., at least 5%, 10%, or 15% CBD) and low in THC (typically less than 0.3%) to be used for specific medical purposes (typically intractable epilepsy) as approved or recommended by a healthcare professional (See list of states on ProCon.org). However, these state laws do not make the general sale of such products legal, and some specifically require that the products be purchased out-of-state.
Side effects and safety concerns:
CBD can cause side effects and interact with certain medications and conditions, although these effects have typically been reported only with very high daily intake, i.e., hundreds of milligrams daily.
- High daily doses of CBD (20 mg per kg of body weight, i.e., hundreds of milligrams) may cause decreased appetite, diarrhea, vomiting, fatigue, fever, somnolence, and abnormal results on liver-function tests (Devinsky, New Eng J Med 2017; Thiele, Lancet 2018).
- CBD at a dose of 300 mg has been shown to worsen symptoms of Parkinson's disease (Consroe, Int J Neurosci, 1986).
- CBD should be used with caution with sedative and sleep-inducing medications, as it may enhance their effects.
- CBD can increase blood serum levels of antiepleptic drugs (Gaston, Epilepsia 2017). CBD may increase the blood-thinning effects of warfarin (Coumadin, Jantoven) likely because CBD competes for the same liver enzymes that break down warfarin and other drugs. This was observed in a man with post-stroke epilepsy taking warfarin: His INR (a measure of how long it takes blood to clot) began increasing several weeks after starting CBD (Epidiolex, Greenwich Biosciences, Inc.) for his seizures. His CBD dosing started with several hundred milligrams daily and increased to over 1,000 mg, at which point his warfarin dose had been reduced by approximately 30% (Grayson, Epilepsy Behav Case Rep 2017).
CBD Oil and Supplements with CL founder, Dr. Tod Cooperman
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