The endocannabinoid system and neuropathic pain

PCC0208009, an indirect IDO1 inhibitor, alleviates neuropathic pain and co-morbidities by regulating synaptic plasticity of ACC and amygdala

BACKGROUND AND PURPOSE

Indoleamine 2, 3-dioxygenase 1 (IDO1) has been linked to neuropathic pain and IDO1 inhibitors have been shown to reduce pain in animals. Some studies have indicated that IDO1 expression increased after neuropathic pain in hippocampus and spinal cord, whether these changes existing in anterior cingulate cortex (ACC) and amygdala remains obscure and how IDO1 inhibition leads to analgesia is largely unknown. Here, we evaluated the antinociceptive effect of PCC0208009, an indirect IDO1 inhibitor, on neuropathic pain and examined the related neurobiological mechanisms.

EXPERIMENTAL APPROACH

The effects of PCC0208009 on pain, cognition and anxiogenic behaviors were evaluated in a rat model of neuropathic pain. Motor disorder, sedation and somnolence were also assessed. Biochemical techniques were used to measure IDO1-mediated signaling changes in ACC and amygdala.

KEY RESULTS

In rats receiving spinal nerve ligation (SNL), IDO1 expression level was increased in ACC and amygdala. PCC0208009 attenuated pain-related behaviors in the formalin test and SNL model and increased cognition and anxiogenic behaviors in SNL rats at doses that did not affect locomotor activity and sleeping. PCC0208009 inhibited IDO1 expression in ACC and amygdala by inhibiting the IL-6-JAK2/STAT3-IDO1-GCN2-IL-6 pathway. In addition, PCC0208009 reversed synaptic plasticity at the functional and structural levels by suppressing NMDA2B receptor and CDK5/MAP2 or CDK5/Tau pathway in ACC and amygdala.

CONCLUSION AND IMPLICATIONS

These results support the role of IDO1-mediated molecular mechanisms in neuropathic pain and suggest that the IDO1 inhibitor PCC0208009 demonstrates selective pain suppression and could be a useful pharmacological therapy for neuropathic pain.

Targeting Peripherally Restricted Cannabinoid Receptor 1, Cannabinoid Receptor 2, and Endocannabinoid-Degrading Enzymes for the Treatment of Neuropathic Pain Including Neuropathic Orofacial Pain

Neuropathic pain conditions including neuropathic orofacial pain (NOP) are difficult to treat. Contemporary therapeutic agents for neuropathic pain are often ineffective in relieving pain and are associated with various adverse effects. Finding new options for treating neuropathic pain is a major priority in pain-related research. Cannabinoid-based therapeutic strategies have emerged as promising new options. Cannabinoids mainly act on cannabinoid 1 (CB1) and 2 (CB2) receptors, and the former is widely distributed in the brain. The therapeutic significance of cannabinoids is masked by their adverse effects including sedation, motor impairment, addiction and cognitive impairment, which are thought to be mediated by CB1 receptors in the brain. Alternative approaches have been developed to overcome this problem by selectively targeting CB2 receptors, peripherally restricted CB1 receptors and endocannabinoids that may be locally synthesized on demand at sites where their actions are pertinent. Many preclinical studies have reported that these strategies are effective for treating neuropathic pain and produce no or minimal side effects. Recently, we observed that inhibition of degradation of a major endocannabinoid, 2-arachydonoylglycerol, can attenuate NOP following trigeminal nerve injury in mice. This review will discuss the above-mentioned alternative approaches that show potential for treating neuropathic pain including NOP.

A Review of Scientific Evidence for THC:CBD Oromucosal Spray (Nabiximols) in the Management of Chronic Pain

The 20% prevalence of chronic pain in the general population is a major health concern given the often profound associated impairment of daily activities, employment status, and health-related quality of life in sufferers. Resource utilization associated with chronic pain represents an enormous burden for healthcare systems. Although analgesia based on the World Health Organization’s pain ladder continues to be the mainstay of chronic pain management, aside from chronic cancer pain or end-of-life care, prolonged use of non-steroidal anti-inflammatory drugs or opioids to manage chronic pain is rarely sustainable. As the endocannabinoid system is known to control pain at peripheral, spinal, and supraspinal levels, interest in medical use of cannabis is growing. A proprietary blend of cannabis plant extracts containing delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) as the principal cannabinoids is formulated as an oromucosal spray (USAN name: nabiximols) and standardized to ensure quality, consistency and stability. This review examines evidence for THC:CBD oromucosal spray (nabiximols) in the management of chronic pain conditions. Cumulative evidence from clinical trials and an exploratory analysis of the German Pain e-Registry suggests that add-on THC:CBD oromucosal spray (nabiximols) may have a role in managing chronic neuropathic pain, although further precise clinical trials are required to draw definitive conclusions.

Challenges and Opportunities in Preclinical Research of Synthetic Cannabinoids for Pain Therapy

Cannabis has been used in pain management since 2900 BC. In the 20th century, synthetic cannabinoids began to emerge, thus opening the way for improved efficacy. The search for new forms of synthetic cannabinoids continues and, as such, the aim of this review is to provide a comprehensive tool for the research and development of this promising class of drugs. Methods for the in vitro assessment of cytotoxic, mutagenic or developmental effects are presented, followed by the main in vivo pain models used in cannabis research and the results yielded by different types of administration (systemic versus intrathecal versus inhalation). Animal models designed for assessing side-effects and long-term uses are also discussed. In the second part of this review, pharmacokinetic and pharmacodynamic studies of synthetic cannabinoid biodistribution, together with liquid chromatography–mass spectrometric identification of synthetic cannabinoids in biological fluids from rodents to humans are presented. Last, but not least, different strategies for improving the solubility and physicochemical stability of synthetic cannabinoids and their potential impact on pain management are discussed. In conclusion, synthetic cannabinoids are one of the most promising classes of drugs in pain medicine, and preclinical research should focus on identifying new and improved alternatives for a better clinical and preclinical outcome.

Aging circadian rhythms and cannabinoids

Numerous aspects of mammalian physiology exhibit cyclic daily patterns known as circadian rhythms. However, studies in aged humans and animals indicate that these physiological rhythms are not consistent throughout the life span. The simultaneous development of disrupted circadian rhythms and age-related impairments suggests a shared mechanism, which may be amenable to therapeutic intervention. Recently, the endocannabinoid system has emerged as a complex signaling network, which regulates numerous aspects of circadian physiology relevant to the neurobiology of aging. Agonists of cannabinoid receptor-1 (CB1) have consistently been shown to decrease neuronal activity, core body temperature, locomotion, and cognitive function. Paradoxically, several lines of evidence now suggest that very low doses of cannabinoids are beneficial in advanced age. One potential explanation for this phenomenon is that these drugs exhibit hormesis-a biphasic dose-response wherein low doses produce the opposite effects of higher doses. Therefore, it is important to determine the dose-, age-, and time-dependent effects of these substances on the regulation of circadian rhythms and other processes dysregulated in aging. This review highlights 3 fields-biological aging, circadian rhythms, and endocannabinoid signaling-to critically assess the therapeutic potential of endocannabinoid modulation in aged individuals. If the hormetic properties of exogenous cannabinoids are confirmed, we conclude that precise administration of these compounds may bidirectionally entrain central and peripheral circadian clocks and benefit multiple aspects of aging physiology.

[Cannabis and cannabinoids-easier access, hype and disappointment : What has been confirmed in therapy?]

BACKGROUND

Cannabis products are being increasingly liberalized all over the world and there is a huge interest in cannabis-based medicine.

OBJECTIVES

Presentation of current studies on the efficacy of different cannabis-based medicine for the treatment of various diseases CURRENT DATA: In German pharmaceutical legislation, nabiximols is approved for the treatment of moderate to severe therapy-resistant spasticity in multiple sclerosis and nabilone is approved for the treatment of therapy-resistant chemotherapy-associated nausea and vomiting. In case of therapy failure cannabinoids, as part of an individual therapeutic attempt, may be considered for the treatment of chronic pain (neuropathic pain, cancer pain, non-neuropathic noncancer pain), cachexia in human immunodeficiency virus as well as for Dravet and Lennox-Gastaut syndrome. From the authors' perspective there is not enough evidence for the use in chemotherapy-associated nausea and vomiting and chronic non-neuropathic pain.

CONCLUSIONS

Currently, a wide use of cannabinoids does not seem probable in the near future. Further studies involving more patients and evaluating long-term effects are necessary.

Therapeutic Effect of the Substrate-Selective COX-2 Inhibitor IMMA in the Animal Model of Chronic Constriction Injury

Enhancement of endocannabinoid signaling has emerged as an attractive strategy for the treatment of pain. In addition to the well-characterized hydrolytic pathways, cyclooxygenase-2 (COX-2) mediated oxygenation is thought to be an alternative route for endocannabinoid metabolism and therefore provides a new avenue for drug intervention. In this study, we examined the therapeutic effect of indomethacin morpholinamide (IMMA), a novel substrate-selective COX-2 inhibitor, in the chronic constriction injury (CCI) mouse model. Treatment with IMMA significantly alleviated hyperalgesia and mechanical allodynia demonstrated by increased thermal withdrawal latency in Hargreaves test and tactile thresholds in Von Frey test. Accumulation of astrocytes and microglia in spinal cord dorsal horn and infiltration of macrophages into the dorsal root ganglion and sciatic nerve were reduced by drug treatment. Co-administration of the CB2 receptor antagonist, but not the CB1 receptor antagonist partially reversed the inhibitory effect of IMMA on pain sensitivity and inflammatory infiltrates. IMMA downregulated the mRNA expression of TNF-α and IL-1β and the production of IL-6 and MCP-1 proteins in the ipsilateral sciatic nerve. The enhanced NF-κB DNA binding activity in the CCI mouse dorsal spinal cord was also significantly reduced, suggesting that inactivation of NF-κB contributes to the anti-inflammatory property of IMMA. However, different from the previous reports showing that IMMA can increase endocannabinoids without interfering with arachidonic acid metabolism, treatment with IMMA failed to elevate the endogenous levels of AEA and 2-AG, but significantly reduced the production of prostaglandin E₂ (PGE₂). Furthermore, the mRNA expression of enzymes involved in PGE₂ production, COX-2 and prostaglandin E synthase 2 in the ipsilateral sciatic nerve was also suppressed by IMMA treatment. Taken together, these results suggested that IMMA might exert anti-nociceptive effects through multiple mechanisms which include, but are not limited to, CB2 receptor activation and reduced PGE₂ production.

Cannabinoids and spinal cord stimulation for the treatment of failed back surgery syndrome refractory pain

Objective

This study aimed to evaluate pain and its symptoms in patients with failed back surgery syndrome (FBSS) refractory to other therapies, treated with a combination of delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD), in association with spinal cord stimulation (SCS).

Settings

Outpatients referred at Pain Unit of San Vincenzo Hospital in Taormina (Italy), between September 2014 and January 2016.

Subjects

Eleven FBSS patients diagnosed with neuropathic pain using the Douleur Neuropathique 4 questionnaire and suffering from moderate to severe chronic refractory pain, and undergoing treatment with SCS and a combination of THC/CBD for 12 consecutive months.

Materials and methods

All the included patients discontinued previous unsuccessful therapy at least 2 months before the beginning of the cannabinoid therapy, with the exception of the SCS that was continued. Patients received a fixed dosage of cannabinoid agonists (THC/CBD) that could be increased subjective to pain control response. A Brief Pain Inventory questionnaire was administered to measure pain and its interference with characteristic dimensions of feelings and functions. The duration of treatment with SCS and THC/CBD combination was 12 months.

Results

Effective pain management as compared to baseline result was achieved in all the cases studied. The positive effect of cannabinoid agonists on refractory pain was maintained during the entire duration of treatment with minimal dosage titration. Pain perception, evaluated through numeric rating scale, decreased from a baseline mean value of 8.18±1.07–4.72±0.9 by the end of the study duration (12 months) (P<0.001).

Conclusion

The results indicate that cannabinoid agonists (THC/CBD) can have remarkable analgesic capabilities, as adjuvant of SCS, for the treatment of chronic refractory pain of FBSS patients.

Cannabinoids and agmatine as potential therapeutic alternatives for cisplatin-induced peripheral neuropathy

Cisplatin is a widely used antineoplastic agent in the treatment of various cancers. Peripheral neuropathy is a well-known side effect of cisplatin and has the potential to result in limiting and/or reducing the dose, decreasing the quality of life. Unfortunately, the mechanism for cisplatin-induced neuropathy has not been completely elucidated. Currently, available treatments for neuropathic pain (NP) are mostly symptomatic, insufficient and are often linked with several detrimental side effects; thus, effective treatments are needed. Cannabinoids and agmatine are endogenous modulators that are implicated in painful states. This review explains the cisplatin-induced neuropathy and antinociceptive effects of cannabinoids and agmatine in animal models of NP and their putative therapeutic potential in cisplatin-induced neuropathy.

The Cannabinoids Δ8THC, CBD, and HU-308 Act via Distinct Receptors to Reduce Corneal Pain and Inflammation

Background and Purpose: Corneal injury can result in dysfunction of corneal nociceptive signaling and corneal sensitization. Activation of the endocannabinoid system has been reported to be analgesic and anti-inflammatory. The purpose of this research was to investigate the antinociceptive and anti-inflammatory effects of cannabinoids with reported actions at cannabinoid 1 (CB₁R) and cannabinoid 2 (CB₂R) receptors and/or noncannabinoid receptors in an experimental model of corneal hyperalgesia.

Methods: Corneal hyperalgesia (increased pain response) was generated using chemical cauterization of the corneal epithelium in wild-type (WT) and CB₂R knockout (CB₂R^−/−) mice. Cauterized eyes were treated topically with the phytocannabinoids Δ⁸-tetrahydrocannabinol (Δ⁸THC) or cannabidiol (CBD), or the CBD derivative HU-308, in the presence or absence of the CB₁R antagonist AM251 (2.0 mg/kg i.p.), or the 5-HT_1A receptor antagonist WAY100635 (1 mg/kg i.p.). Behavioral pain responses to a topical capsaicin challenge at 6 h postinjury were quantified from video recordings. Mice were euthanized at 6 and 12 h postcorneal injury for immunohistochemical analysis to quantify corneal neutrophil infiltration.

Results: Corneal cauterization resulted in hyperalgesia to capsaicin at 6 h postinjury compared to sham control eyes. Neutrophil infiltration, indicative of inflammation, was apparent at 6 and 12 h postinjury in WT mice. Application of Δ⁸THC, CBD, and HU-308 reduced the pain score and neutrophil infiltration in WT mice. The antinociceptive and anti-inflammatory actions of Δ⁸THC, but not CBD, were blocked by the CB₁R antagonist AM251, but were still apparent, for both cannabinoids, in CB₂R^−/− mice. However, the antinociceptive and anti-inflammatory actions of HU-308 were absent in the CB₂R^−/− mice. The antinociceptive and anti-inflammatory effects of CBD were blocked by the 5-HT_1A antagonist WAY100635.

Conclusion: Topical cannabinoids reduce corneal hyperalgesia and inflammation. The antinociceptive and anti-inflammatory effects of Δ⁸THC are mediated primarily via CB₁R, whereas that of the cannabinoids CBD and HU-308, involve activation of 5-HT_1A receptors and CB₂Rs, respectively. Cannabinoids could be a novel clinical therapy for corneal pain and inflammation resulting from ocular surface injury.

CB1 cannabinoid receptor agonist mouse VD-hemopressin(α) produced supraspinal analgesic activity in the preclinical models of pain

Mouse VD-hemopressin(α) (VD-Hpα) is an undecapeptide that selectively activates CB₁ cannabinoid receptor in in vitro functional tests, and exerts CB₁-mediated central antinociception in the mouse tail-flick assay. The aim of the present study was to further investigate the analgesic properties of supraspinal mouse VD-Hpα in a range of preclinical pain models. Our results indicated that the classical cannabinoid agonist WIN 55,212-2 produced supraspinal analgesia in preclinical pain models, which was selectively antagonized by the CB₁ antagonist/inverse agonist AM251, but not by the CB₂ antagonist AM630. In contrast, in post-operative pain model and phase I of formalin test, intracerebroventricular administration of mouse VD-Hpα induced dose-related analgesia in mice, which were markedly reduced by pretreatment with the CB₁ neutral antagonist AM4113, but not AM251, AM630 and the selective antagonists of opioid and Transient Receptor Potential Vanilloid Type 1 (TRPV₁) receptors. Furthermore, in the acetic acid-induced visceral pain model, supraspinal administration of mouse VD-Hpα dose-dependently produced analgesic activities and the effects were significantly antagonized by both AM4113 and the TRPV₁ receptor antagonist SB366791, but not AM251, AM630 and naloxone. In addition, central injection of mouse VD-Hpα did not have significant effect in phase II of formalin test. Taken together, the present work suggests that the CB₁ receptor peptidic agonist mouse VD-Hpα produces supraspinal analgesia in preclinical pain models via a novel CB₁ receptor-mediated mechanism, in a manner pharmacologically dissociable from WIN 55,212-2. In addition, TRPV₁ receptor might also be involved in mouse VD-Hpα-induced analgesia in a visceral pain model.

Rare genetic variants in the endocannabinoid system genes CNR1 and DAGLA are associated with neurological phenotypes in humans

Rare genetic variants in the core endocannabinoid system genes CNR1, CNR2, DAGLA, MGLL and FAAH were identified in molecular testing data from 6,032 patients with a broad spectrum of neurological disorders. The variants were evaluated for association with phenotypes similar to those observed in the orthologous gene knockouts in mice. Heterozygous rare coding variants in CNR1, which encodes the type 1 cannabinoid receptor (CB1), were found to be significantly associated with pain sensitivity (especially migraine), sleep and memory disorders—alone or in combination with anxiety—compared to a set of controls without such CNR1 variants. Similarly, heterozygous rare variants in DAGLA, which encodes diacylglycerol lipase alpha, were found to be significantly associated with seizures and neurodevelopmental disorders, including autism and abnormalities of brain morphology, compared to controls. Rare variants in MGLL, FAAH and CNR2 were not associated with any neurological phenotypes in the patients tested. Diacylglycerol lipase alpha synthesizes the endocannabinoid 2-AG in the brain, which interacts with CB1 receptors. The phenotypes associated with rare CNR1 variants are reminiscent of those implicated in the theory of clinical endocannabinoid deficiency syndrome. The severe phenotypes associated with rare DAGLA variants underscore the critical role of rapid 2-AG synthesis and the endocannabinoid system in regulating neurological function and development. Mapping of the variants to the 3D structure of the type 1 cannabinoid receptor, or primary structure of diacylglycerol lipase alpha, reveals clustering of variants in certain structural regions and is consistent with impacts to function.

Antinociceptive effects of HUF-101, a fluorinated cannabidiol derivative

Cannabidiol (CBD) is a phytocannabinoid with multiple pharmacological effects and several potential therapeutic properties. Its low oral bioavailability, however, can limit its clinical use. Preliminary results indicate that fluorination of the CBD molecule increases its pharmacological potency. Here, we investigated whether HUF-101 (3, 10, and 30mg/kg), a fluorinated CBD analogue, would induce antinociceptive effects. HUF-101 effects were compared to those induced by CBD (10, 30, and 90mg/kg) and the cannabinoid CB_1/2 receptor agonist WIN55,212-2 (1, 3, and 5mg/kg). These drugs were tested in male Swiss mice submitted to the following models predictive to antinociceptive drugs: hot plate, acetic acid-induced writhing, and carrageenan-induced inflammatory hyperalgesia. To evaluate the involvement of CB₁ and CB₂ receptors in HUF-101 and CBD effects, mice received the CB₁ receptor antagonist AM251 (1 or 3mg/kg) or the CB₂ receptor antagonist AM630 (1 or 3mg/kg) 30min before HUF-101, CBD, or WIN55,212-2. In the hot plate test, HUF-101 (30mg/kg) and WIN55,212-2 (5mg/kg) induced antinociceptive effects, which were attenuated by the pretreatment with AM251 and AM630. In the abdominal writhing test, CBD (30 and 90mg/kg), HUF-101 (30mg/kg), and WIN55,212-2 (3 and 5mg/kg) induced antinociceptive effects indicated by a reduction in the number of writhing. Whereas the pretreatment with AM630 did not mitigate the effects induced by any drug in this test, the pretreatment with AM251 attenuated the effect caused by WIN55,212-2. In the carrageenan-induced hyperalgesia test, CBD (30 and 90mg/kg), HUF-101 (3, 10 and 30mg/kg) and WIN55,212-2 (1mg/kg) decreased the intensity of mechanical hyperalgesia measured by the electronic von Frey method. The effects of all compounds were attenuated by the pretreatment with AM251 and AM630. Additionally, we evaluated whether HUF-101 would induce the classic cannabinoid CB₁ receptor-mediated tetrad (hypolocomotion, catalepsy, hypothermia, and antinociception). Unlike WIN55,212-2, CBD and HUF-101 did not induce the cannabinoid tetrad. These findings show that HUF-101 produced antinociceptive effects at lower doses than CBD, indicating that the addition of fluoride improved its pharmacological profile. Furthermore, some of the antinociceptive effects of CBD and HUF-101 effects seem to involve the activation of CB₁ and CB₂ receptors.

Fundamentals of and Critical Issues in Lipid Autacoid Medicine: A Review

The identification of a number of families of lipid signal molecules since the 1990s created new therapeutic possibilities for a great number of disorders characterized by chronic inflammation and pain. These lipid autacoids have been explored in a great variety of animal models related to inflammation, pain, (neuro-)protection, and repair. Based on the data from these models, as well as on a number of proof of principle studies in the clinic in indications such as neuropathic pain, a new chapter in medicine is about to begin. We would like to introduce the term “Autacoid Pain Medicine” for this chapter. There are, however, a number of methodological and strategic issues to overcome in this field. One of the roadblocks is related to patent strategies around families of these molecules. As this is not always recognized we will present a number of examples.

The endocannabinoid system, a novel and key participant in acupuncture's multiple beneficial effects

Acupuncture and its modified forms have been used to treat multiple medical conditions, but whether the diverse effects of acupuncture are intrinsically linked at the cellular and molecular level and how they might be connected have yet to be determined. Recently, an emerging role for the endocannabinoid system (ECS) in the regulation of a variety of physiological/pathological conditions has been identified. Overlap between the biological and therapeutic effects induced by ECS activation and acupuncture has facilitated investigations into the participation of ECS in the acupuncture-induced beneficial effects, which have shed light on the idea that the ECS may be a primary mediator and regulatory factor of acupuncture's beneficial effects. This review seeks to provide a comprehensive summary of the existing literature concerning the role of endocannabinoid signaling in the various effects of acupuncture, and suggests a novel notion that acupuncture may restore homeostasis under different pathological conditions by regulating similar networks of signaling pathways, resulting in the activation of different reaction cascades in specific tissues in response to pathological insults.

Cannabinoids therapeutic use: what is our current understanding following the introduction of THC, THC:CBD oromucosal spray and others?

INTRODUCTION

The complexity of the endocannabinoid (eCB) system is becoming better understood and new drivers of eCB signaling are emerging. Modulation of the activities of the eCB system can be therapeutic in a number of diseases. Research into the eCB system has been paralleled by the development of agents that interact with cannabinoid receptors. In this regard it should be remembered that herbal cannabis contains a myriad of active ingredients, and the individual cannabinoids have quite distinct biological activities requiring independent studies. Areas covered: This article reviews the most important current data involving the eCB system in relation to human diseases, to reflect the present (based mainly on the most used prescription cannabinoid medicine, THC/CBD oromucosal spray) and potential future uses of cannabinoid-based therapy. Expert commentary: From the different therapeutic possibilities, THC/CBD oromucosal spray has been in clinical use for approximately five years in numerous countries world-wide for the management of multiple sclerosis (MS)-related moderate to severe resistant spasticity. Clinical trials have confirmed its efficacy and tolerability. Other diseases in which different cannabinoids are currently being investigated include various pain states, Alzheimer's disease, Parkinson's disease, Huntington's disease and epilepsy. The continued characterization of individual cannabinoids in different diseases remains important.

Medical Marijuana: Just the Beginning of a Long, Strange Trip?

Medical marijuana continues to gain acceptance and become legalized in many states. Various species of the marijuana plant have been cultivated, and this plant can contain up to 100 active compounds known as cannabinoids. Two cannabinoids seem the most clinically relevant: Δ9-tetrahydrocannabinol (THC), which tends to produce the psychotropic effects commonly associated with marijuana, and cannabidiol (CBD), which may produce therapeutic effects without appreciable psychoactive properties. Smoking marijuana, or ingesting extracts from the whole plant orally (in baked goods, teas, and so forth), introduces variable amounts of THC, CBD, and other minor cannabinoids into the systemic circulation, where they ultimately reach the central and peripheral nervous systems. Alternatively, products containing THC, CBD, or a combination of both compounds, can be ingested as oral tablets or via sprays applied to the oral mucosal membranes. These products may provide a more predictable method for delivering a known amount of specific cannabinoids into the body. Although there is still a need for randomized controlled trials, preliminary studies have suggested that medical marijuana and related cannabinoids may be beneficial in treating people with chronic pain, inflammation, spasticity, and other conditions seen commonly in physical therapist practice. Physical therapists, therefore, should be aware of the options that are available for patients considering medical marijuana and should be ready to provide information for these patients. Clinicians also should be aware that marijuana can produce untoward effects on cognition, coordination, balance, and cardiovascular and pulmonary function and should be vigilant for any problems that may arise if patients are using cannabinoids during physical rehabilitation.