A number of studies over the last two decades or more have reported that CBD has anti-seizure activity, reducing the severity of seizures in animal models. In addition, there have been a number of case studies and anecdotal reports suggesting that CBD may be effective in treating children with drug-resistant epilepsy. However, there have only been a few small randomized clinical trials examining the efficacy of CBD as a treatment for epilepsy; the total number of subjects enrolled in these studies was 48. Three of the four studies reported positive results, including decreased frequency of seizures. However, the studies suffered from significant design flaws, including failure to fully quantify baseline seizure frequency, inadequate statistical analysis, and a lack of sufficient detail to adequately evaluate and interpret the findings.Therefore, the currently available information is insufficient to draw firm conclusions regarding the efficacy of CBD as a treatment for epilepsy; a recent Cochrane review concluded, there is a need for “a series of properly designed, high quality, and adequately powered trials.
NIDA is currently collaborating with the National Institute of Neurological Disorders and Stroke to evaluate CBD in animal models of epilepsy in order to understand the underlying mechanisms and optimize the conditions under which CBD may treat seizure disorders, and determine whether it works synergistically with other anti-seizure medications. In addition, clinical trials are currently underway by GW Pharmaceuticals, testing the efficacy of Epidiolex, a purified CBD extract, for treatment of pediatric epilepsy.
Neuroprotective and Anti-Inflammatory Effects
CBD has also been shown to have neuroprotective properties in cell cultures as well as in animal models of several neurodegenerative diseases, including Alzheimer’s, stroke, glutamate toxicity, multiple sclerosis (MS), Parkinson’s disease, and neurodegeneration caused by alcohol abuse.Nabiximols (trade name Sativex), which contains THC and CBD in roughly equal proportions, has been approved throughout most of Europe and in a number of other countries for the treatment of spasticity associated with MS. It has not been approved in the United States, but clinical trials are ongoing, and two recent studies reported that nabiximols reduced the severity of spasticity in MS patients. There have been limited clinical trials to assess the potential efficacy of CBD for the other indications highlighted; however, a recent small double-blind trial in patients with Parkinson’s disease found the CBD improved quality-of-life scores.
There have been multiple clinical trials demonstrating the efficacy of nabiximols on central and peripheral neuropathic pain, rheumatoid arthritis, and cancer pain. In addition, nabiximols is currently approved in Canada for the treatment of central neuropathic pain in MS and cancer pain unresponsive to opioid therapy. However, the current evidence suggests that the analgesia is mediated by THC and it is unclear whether CBD contributes to the therapeutic effects. THC alone has been shown to reduce pain; we are unaware of clinical studies that have explored the efficacy of CBD alone on pain. However, the anti-inflammatory properties of CBD (discussed above) could be predicted to play a role in the analgesic effects of nabiximols. Recent research has also suggested that cannabinoids and opioids have different mechanisms for reducing pain and that their effects may be additive, which suggests that combination therapies may be developed that may have reduced risks compared to current opioid therapies. However, this work is very preliminary.
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