Medical Marijuana for Pets
Cannabidiol: Barriers to Research and Potential Medical Benefits
To date, 23 states and the District of Columbia have passed laws allowing marijuana to be used for a variety of medical conditions. Fifteen additional states have enacted laws intended to allow access to CBD oil and/or high-CBD strains of marijuana. Interest in the potential therapeutic effects of CBD has been growing rapidly, partially in response to media attention surrounding the use of CBD oil in young children with intractable seizure disorders including Dravet syndrome and Lennox-Gastaut syndrome. While there are promising preliminary data, the scientific literature is currently insufficient to either prove or disprove the efficacy and safety of CBD in patients with epilepsy.i and further clinical evaluation is warranted. In addition to epilepsy, the therapeutic potential of CBD is currently being explored for a number of indications including anxiety disorders, substance use disorders, schizophrenia, cancer, pain, inflammatory diseases and others. My testimony will provide an overview of what the science tells us about the therapeutic potential of CBD and of the ongoing research supported by NIH in this area.
CBD Biology and Therapeutic Rationale
CBD is one of more than 80 active cannabinoid chemicals in the marijuana plant.ii Unlike the main psychoactive cannabinoid in marijuana, tetrahydrocannabinol (THC), CBD does not produce euphoria or intoxication.iii,iv,v Cannabin
oids have their effect mainly by interacting with specific receptors on cells in the brain and body: the CB1 receptor, found on neurons and glial cells in various parts of the brain, and the CB2 receptor, found mainly in the body’s immune system. The euphoric effects of THC are caused by its activation of CB1 receptors. CBD has a very low affinity for these receptors (100 fold less than THC) and when it binds it produces little to no effect. There is also growing evidence that CBD acts on other brain signaling systems, and that these actions may be important contributors to its therapeutic effects.ii
Preclinical and Clinical Evidence
Rigorous clinical studies are still needed to evaluate the clinical potential of CBD for specific conditions.i However, pre-clinical research (including both cell culture and animal models) has shown CBD to have a range of effects that may be therapeutically useful, including anti-seizure, antioxidant, neuroprotective, anti-inflammatory, analgesic, anti-tumor, anti-psychotic, and anti-anxiety properties.
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.vi,vii 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.viii,ix,x 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.viiiTherefore, 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.”xi NIDA is currently collaborating with the National Institute on 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,xii,xiii,xiv strok
e,xvglutamate toxicity,xvi multiple sclerosis (MS),xvii Parkinson’s disease,xviii and neurodegeneration caused by alcohol abuse.xix 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.xx,xxi 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.xxii
There have been multiple clinical trials demonstrating the efficacy of nabiximols on central and peripheral neuropathic pain, rheumatoid arthritis, and cancer pain.xxiii 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.xxiv THC alone has been shown to reduce pain;xxv,xxvi 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.xxvii
In addition to the research on the use of cannabinoids in palliative treatments for cancer—reducing pain and nausea and in increasing appetite—there are also several pre-clinical reports showing anti-tumor effects of CBD in cell culture and in animal models.xxviii These studies have found reduced cell viability, increased cancer cell death, decreased tumor growth, and inhibition of metastasis (reviewed in McAllister et al, 2015).xxix These effects may be due to the antioxidant and anti-inflammatory effects of CBD;xxx however these findings have not yet been explored in human patients. There are multiple industry sponsored clinical trials underway to begin to test the efficacy of CBD in human cancer patients.
Marijuana can produce acute psychotic episodes at high doses, and several studies have linked marijuana use to increased risk for chronic psychosis in individuals with specific genetic risk factors. Research suggests that these effects are mediated by THC, and it has been suggested that CBD may mitigate these effects.xxxi There have been a few small-scale clinical trials in which patients with psychotic symptoms were treated with CBD, including case reports of patients with schizophrenia that reported conflicting results; a small case study in patients with Parkinson’s disease with psychosis, which reported positive results; and one small randomized clinical trial reporting clinical improvement in patients with schizophrenia treated with CBD.xxxiiLarge randomized clinical trials would be needed to fully evaluate the therapeutic potential of CBD for patients with schizophrenia and other forms of psychosis.
CBD has shown therapeutic efficacy in a range of animal models of anxiety and stress, reducing both behavioral and physiological (e.g., heart rate) measures of stress and anxiety.xxxiii,xxxiv In addition, CBD has shown efficacy in small human laboratory and clinical trials. THC available from medical marijuana dispensaries
may also reduce anxiety. CBD reduced anxiety in patients with social anxiety subjected to a stressful public speaking task.xxxv In a laboratory protocol designed to model post-traumatic stress disorders, CBD improved “consolidation of extinction learning”, in other words, forgetting of traumatic memories.xxxvi The anxiety-reducing effects of CBD appear to be mediated by alterations in serotonin receptor 1a signaling, although the precise mechanism remains to be elucidated and more research is needed.xxxvii
Efficacy for Treating Substance Use Disorders
Early preclinical findings also suggest that CBD may have therapeutic value as a treatment of substance use disorders. CBD reduced the rewarding effects of morphinexxxviii and reduced cue-induced heroin seekingxxxix in animal models. A few small clinical trials have examined CBD and/or nabiximols (THC/CBD) for the treatment of substance use disorders; however, the available data are not sufficient to draw conclusions. NIDA is supporting multiple ongoing clinical trials in this area.
Safety of CBD
For reasons discussed previously, despite its molecular similarity to THC, CBD only interacts with cannabinoid receptors weakly at very high doses (100 times that of THC),xl and the alterations in thinking and perception caused by THC are not observed with CBD.iii.iv,v The different pharmacological properties of CBD give it a different safety profile from THC. A review of 25 studies on the safety and efficacy of CBD did not identify significant side effects across a wide range of dosages, including acute and chronic dose regimens, using various modes of administration.xli CBD is present in nabiximols which, as noted earlier, is approved throughout most of Europe and in other countries. Because of this, there is extensive information available with regard to its metabolism, toxicology, and safety. However, additional safety testing among specific patient populations may be warranted should an application be made to the Food and Drug Administration.
Research Opportunities and Challenges
This is a critical area for new research. While there is preliminary evidence that CBD may have therapeutic value for a number of conditions, we need to be careful to not get ahead of the evidence. Ninety-five percent of drugs that move from promising preclinical findings to clinical research do not make it to market. The recently announced elimination of the PHS review of non-federally funded research protocols involving marijuana is an important first step to enhance conducting research on marijuana and its components such as CBD. Still, it is important to try to understand the reasons for the lack of well-controlled clinical trials of CBD including: the regulatory requirements associated with doing research with Schedule I substances, including a requirement to demonstrate institutional review board approval; and the lack of CBD that has been produced under the guidance of Current Good Manufacturing Processes (cGMP) – required for testing in human clinical trials – available for researchers. Furthermore, the opportunity to gather important information on clinical outcomes through practical (non-randomized) trials for patients using CBD products available in state marijuana dispensaries is complicated by the variable quality and purity of CBD from these sources.
Ongoing CBD Research
The NIH recognizes the need for additional research on the therapeutic effects of CBD and other cannabinoids, and supports ongoing efforts to reduce barriers to research in this area. NIH is currently supporting a number of studies on the therapeutic effects as well as the health risks of cannabinoids. These include studies of the therapeutic value of CBD for:
- Treatment of substance use disorders (opioids, alcohol, cannabis, methamphetamine)
- Attenuation of the cognitive deficits caused by THC
- Neuropathic pain due to spinal cord injury
- Mitigating the impact of cannabis use on risk for schizophrenia
- Examination of the potential of CBD as an antiepileptic treatment
It is important to note that NIDA’s mission is focused on drug abuse; studies related to the therapeutic effects of CBD in other areas would be funded by the Institute or Center responsible for that program area. For example, studies related to epilepsy will likely be funded by the National Institute of Neurological Disorders and Stroke or by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, while studies related to schizophrenia will likely be funded by the National Institute on Mental Health.
There is significant preliminary research supporting the potential therapeutic value of CBD, and while it is not yet sufficient to support drug approval, it highlights the need for rigorous clinical research in this area. There are barriers that should be addressed to facilitate more research in this area. We appreciate the opportunity to testify on the potential use of CBD for therapeutic purposes. Thank you again for inviting me here today, and I look forward to any questions you may have.
- i Welty et al. Cannabidiol: promise and pitfalls. Epilepsy Curr. 14(5):250-2. (2014).
- ii Borgelt et al. The pharmacologic and clinical effects of medical cannabis. Pharmacotherapy (Review) 33 (2): 195–209 (2013).
- iii Martin-Santos et al. Acute effects of a single, oral dose of d9-tetrahydrocannabinol (THC) and cannabidiol (CBD) administration in healthy volunteers. Curr Pharm Des. 2012;18(32):4966-79.
- iv Fusar-Poli et al. Distinct Effects of Δ9-Tetrahydrocannabinol and Cannabidiol on Neural Activation During Emotional Processing. Arch Gen Psychiatry. 2009;66(1):95-105.
- v Winton-Brown et al. Modulation of Auditory and Visual Processing by Delta-9-Tetrahydrocannabinol and Cannabidiol: an fMRI Study. Neuropsychopharmacology. 2011 Jun;36(7):1340-8.
- vi Jones et al. Cannabidiol exerts anti-convulsant effects in animal models of temporal lobe and partial seizures. Seizure. 2012 Jun;21(5):344-52.
- vii Consroe P and Wolkin A. Cannabidiol--antiepileptic drug comparisons and interactions in experimentally induced seizures in rats. J Pharmacol Exp Ther. 1977 Apr;201(1):26-32.
- viii Porter BE and Jacobson C. Report of a parent survey of cannabidiol-enriched cannabis use in pediatric treatment-resistant epilepsy. Epilepsy & Behavior 29 (2013) 574–577.
- ix Press et al. Parental reporting of response to oral cannabis extracts for treatment of refractory epilepsy. Epilepsy & Behavior 45 (2015) 49–52.
- x Hussain et al. Perceived efficacy of cannabidiol-enriched cannabis extracts for treatment of pediatric epilepsy: A potential role for infantile spasms and Lennox-Gastaut syndrome. Epilepsy Behav. 2015 Apr 29. pii: S1525-5050(15)00157-2.
- xi Gloss and Vickrey B. Cannabinoids for epilepsy. Cochrane Database Syst Rev. 3:CD009270. (2014).
- xii Esposito G et al. The marijuana component cannabidiol inhibits beta-amyloid-induced tau protein hyperphosphorylation through Wnt/beta-catenin pathway rescue in PC12 cells. J Mol Med (Berl). 84(3):253-8. (2006).
- xiii Martín-Moreno et al. Cannabidiol and Other Cannabinoids Reduce Microglial Activation In Vitro and In Vivo: Relevance to Alzheimer’s Disease. Molecular Pharmacology. 79(6):964-973. (2011).
- xiv Iuvone et al.Neuroprotective effect of cannabidiol, a non-psychoactive component from Cannabis sativa, on beta-amyloid-induced toxicity in PC12 cells. J Neurochem. 89(1):134-41. (2004).
- xv Pazos et al. Mechanisms of cannabidiol neuroprotection in hypoxic-ischemic newborn pigs:role of 5HT(1A) and CB2 receptors. Neuropharmacology. 71:282-91. (2013).
- xvi Hampson et al. Cannabidiol and (-)Delta9-tetrahydrocannabinol are neuroprotective antioxidants. Proc Natl AcadSci U S A.95(14):8268-73. (1998).
- xvii Pryce et al. Neuroprotection inExperimental Autoimmune Encephalomyelitis and Progressive Multiple Sclerosis by Cannabis-Based Cannabinoids. J Neuroimmune Pharmacol. 2014 Dec 24. [Epub ahead of print]
- xviii García-Arencibia et al. Evaluation of the neuroprotective effect of cannabinoids in a rat model of Parkinson's disease: importance of antioxidant and cannabinoid receptor-independent properties. Brain Res. 1134(1):162-70. (2007).
- xix Hamelink et al. Comparison of cannabidiol, antioxidants, and diuretics in reversing binge ethanol-induced neurotoxicity. J Pharmacol Exp Ther. 2005 Aug;314(2):780-8.
- xx Di Marzo and Centonze . Placebo effects in a multiple sclerosis spasticity enriched clinical trial with the oromucosal cannabinoid spray (THC/CBD): dimension and possible causes. CNS Neurosci Ther. 21(3):215-21. (2015).
- xxi Flachenecker et al. Nabiximols (THC/CBD oromucosal spray,Sativex®) in clinical practice--results of a multicenter, non-interventional study (MOVE 2) in patients with multiple sclerosis spasticity. Eur Neurol.71(5-6):271-9. (2014)
- xxii Chagas et al. Effects of cannabidiol in the treatment of patients with Parkinson's disease: an exploratory double-blind trial. J Psychopharmacol. 28(11):1088-98. (2014).
- xxiii Russo EB. Cannabinoids in the management of difficult to treat pain. Therapeutics and Clinical Risk Management. 4(1):245-259.(2008).
- xxiv Iskedjian et al. Meta-analysis of cannabis based treatments for neuropathic and multiple sclerosis-related pain. Curr Med Res Opin. 23(1):17-24.(2007).
- xxv Svendsen et al. Does the cannabinoid dronabinol reduce central pain in multiple sclerosis? Randomised double blind placebo controlled crossover trial. BMJ. 2004 Jul 31;329(7460):253.
- xxvi Portenoy et al. Nabiximols for opioid-treated cancer patients with poorly-controlled chronic pain: a randomized, placebo-controlled, graded-dose trial. J Pain. 2012 May;13(5):438-49.
- xxvii Neelakantan et al. Distinct interactions of cannabidiol and morphine in three nociceptive behavioral models in mice. Behav Pharmacol. 26(3):304-14. (2015).
- xxviii McAllister et al. The Antitumor Activity of Plant-Derived Non-Psychoactive Cannabinoids. J Neuroimmune Pharmacol. 2015 Apr28. [Epub ahead of print]
- xxix McAllister et al. The Antitumor Activity of Plant-Derived Non-Psychoactive Cannabinoids. J Neuroimmune Pharmacol. 2015 Apr28. [Epub ahead of print].
- xxx Massi et al. 5-Lipoxygenase and anandamide hydrolase (FAAH) mediate the antitumor activity of cannabidiol, a non-psychoactive cannabinoid. J Neurochem. 2008 Feb;104(4):1091-100.
- xxxi Wilkinson et al. Impact of Cannabis Use on the Development of Psychotic Disorders. Curr Addict Rep. 2014 Jun 1;1(2):115-128.
- xxxii Iseger and Bossong. A systematic review of the antipsychotic properties of cannabidiol in humans. Schizophr Res. 162(1-3):153-61. (2015).
- xxxiii Guimaraes et al. Antianxiety effect of cannabidiol in the elevated plus-maze. Psychopharmacology (Berl) 100:558–559 (1990).
- xxxiv Lemos et al. Involvement of the prelimbic prefrontal cortex on cannabidiol-induced attenuation of contextual conditioned fear in rats. Behav Brain Res 207:105–111(2010).
- xxxv Bergamaschi et al. Cannabidiol reduces the anxiety induced by simulated public speaking in treatment-naive social phobia patients. Neuropsychopharmacology 2011;36:1219–1226.
- xxxvi Das et al. Cannabidiol enhances consolidation of explicit fear extinction in humans. Psychopharmacology (Berl). 2013 Apr;226(4):781-92.
- xxxvii Campos et al. Involvement of serotonin-mediated neurotransmission in the dorsal periaqueductal gray matter on cannabidiol chronic effects in panic-like responses in rats. Psychopharmacology (Berl). 2013 Mar;226(1):13-24.
- xxxviii Katsidoni et al. Cannabidiol inhibits the reward-facilitating effect of morphine: involvement of 5-HT1A receptors in the dorsal raphe nucleus. Addict Biol. 2013;18(2):286–96.
- xxxix Ren et al. Cannabidiol, a nonpsychotropic component of cannabis, inhibits cue-induced heroin seeking and normalizes discrete mesolimbic neuronal disturbances. J Neurosci. 2009;29(47):14764–9.
- xl Pertwee RG. The diverse CB1 and CB2 receptor pharmacology of three plant cannabinoids: Δ9-tetrahydrocannabinol, cannabidiol and Δ9-tetrahydrocannabivarin. Br J Pharmacol. 2008 Jan; 153(2): 199–215.
- xli Bergamaschi et al. Safety and side effects of cannabidiol, a Cannabis sativa constituent. Curr Drug Saf. 2011 Sep 1;6(4):237-49.