Cannabinoid Pharmacology Research Articles

Decreased Reward Sensitivity in Rats from the Fischer344 Strain Compared to Wistar Rats Is Paralleled by Differences in Endocannabinoid Signaling

BackgroundThe aim of the present study was to examine if differences in the endocannabinoid (ECB) system might be linked to strain specific variations in reward-related behavior in Fischer344 (Fischer) and Wistar rats.Methodology/Principal FindingsTwo rat strains, the Fischer and the Wistar strain, were tested for different aspects of reward sensitivity for a palatable food reward (sweetened condensed milk, SCM) in a limited-access intake test, a progressive ratio (PR) schedule and the pleasure-attenuated startle (PAS) paradigm. Additionally, basic differences in the ECB system and cannabinoid pharmacology were examined in both rat strains. Fischer rats were found to express lower reward sensitivity towards SCM compared to Wistar rats. These differences were observed for consummatory, motivational and hedonic aspects of the palatable food reward. Western blot analysis for the CB1 receptor and the ECB degrading enzyme fatty acid amide hydrolase (FAAH) revealed a lower expression of both proteins in the hippocampus (HPC) of Fischer rats compared to the Wistar strain. Furthermore, increased cannabinoid-stimulated extracellular-regulated kinase (ERK) phosphorylation was detected in Wistar rats compared to the Fischer strain, indicating alterations in ECB signaling. These findings were further supported by the pharmacological results, where Fischer rats were found to be less sensitive towards the effects of the CB1 receptor antagonist/inverse agonist SR141716 and the cannabinoid agonist WIN 55,212-2.Conclusions/SignificanceOur present findings indicate differences in the expression of the CB1 receptor and FAAH, as well as the activation of ECB signaling pathways between Fischer and Wistar rats. These basic differences in the ECB system might contribute to the pronounced differences observed in reward sensitivity between both rat strains.

Here Today, Gone Tomorrow…and Back Again? A Review of Herbal Marijuana Alternatives (K2, Spice), Synthetic Cathinones (Bath Salts), Kratom, Salvia divinorum, Methoxetamine, and Piperazines

Despite their widespread Internet availability and use, many of the new drugs of abuse remain unfamiliar to health care providers. The herbal marijuana alternatives, like K2 or Spice, are a group of herbal blends that contain a mixture of plant matter in addition to chemical grade synthetic cannabinoids. The synthetic cathinones, commonly called "bath salts," have resulted in nationwide emergency department visits for severe agitation, sympathomimetic toxicity, and death. Kratom, a plant product derived from Mitragyna speciosa Korth, has opioid-like effects, and has been used for the treatment of chronic pain and amelioration of opioid-withdrawal symptoms. Salvia divinorum is a hallucinogen with unique pharmacology that has therapeutic potential but has been banned in many states due to concerns regarding its psychiatric effects. Methoxetamine has recently become available via the Internet and is marked as "legal ketamine." Moreover, the piperazine derivatives, a class of amphetamine-like compounds that includes BZP and TMFPP, are making a resurgence as "legal Ecstasy." These psychoactives are available via the Internet, frequently legal, and often perceived as safe by the public. Unfortunately, these drugs often have adverse effects, which range from minimal to life-threatening. Health care providers must be familiar with these important new classes of drugs. This paper discusses the background, pharmacology, clinical effects, detection, and management of synthetic cannabinoid, synthetic cathinone, methoxetamine, and piperazine exposures.

Modulation of l-α-Lysophosphatidylinositol/GPR55 Mitogen-activated Protein Kinase (MAPK) Signaling by Cannabinoids

GPR55 is activated by l-α-lysophosphatidylinositol (LPI) but also by certain cannabinoids. In this study, we investigated the GPR55 pharmacology of various cannabinoids, including analogues of the CB1 receptor antagonist Rimonabant®, CB2 receptor agonists, and Cannabis sativa constituents. To test ERK1/2 phosphorylation, a primary downstream signaling pathway that conveys LPI-induced activation of GPR55, a high throughput system, was established using the AlphaScreen® SureFire® assay. Here, we show that CB1 receptor antagonists can act both as agonists alone and as inhibitors of LPI signaling under the same assay conditions. This study clarifies the controversy surrounding the GPR55-mediated actions of SR141716A; some reports indicate the compound to be an agonist and some report antagonism. In contrast, we report that the CB2 ligand GW405833 behaves as a partial agonist of GPR55 alone and enhances LPI signaling. GPR55 has been implicated in pain transmission, and thus our results suggest that this receptor may be responsible for some of the antinociceptive actions of certain CB2 receptor ligands. The phytocannabinoids Δ9-tetrahydrocannabivarin, cannabidivarin, and cannabigerovarin are also potent inhibitors of LPI. These Cannabis sativa constituents may represent novel therapeutics targeting GPR55.

Cannabis in sport: anti-doping perspective.

Since 2004, when the World Anti-Doping Agency assumed the responsibility for establishing and maintaining the list of prohibited substances and methods in sport (i.e. the Prohibited List), cannabinoids have been prohibited in all sports during competition. The basis for this prohibition can be found in the World Anti-Doping Code, which defines the three criteria used to consider banning a substance. In this context, we discuss the potential of cannabis to enhance sports performance, the risk it poses to the athlete's health and its violation of the spirit of sport. Although these compounds are prohibited in-competition only, we explain why the pharmacokinetics of their main psychoactive compound, Δ(9)-tetrahydrocannabinol, may complicate the results management of adverse analytical findings. Passive inhalation does not appear to be a plausible explanation for a positive test. Although the prohibition of cannabinoids in sports is one of the most controversial issues in anti-doping, in this review we stress the reasons behind this prohibition, with strong emphasis on the evolving knowledge of cannabinoid pharmacology.

A survey study to characterize use of Spice products (synthetic cannabinoids)

Background Synthetic cannabinoids are a rapidly emerging class of abused drugs. Synthetic cannabinoids are typically sold as “herbal blends” or “incense,” commonly referred to as Spice products. No controlled human experiments have been conducted on the effects of Spice products or the synthetic cannabinoids they often contain. Methods An internet-based survey study was conducted with adults reporting at least one lifetime use of a Spice product. Results Respondents were primarily male, Caucasian and ≥12 years of education. Use of other psychoactive drugs was common, though 21% identified Spice products as their preferred drug. Spice products were most frequently obtained from retail vendors and smoked, though other forms of ingestion were endorsed. Mean age of first use was 26 and mean frequency of use in the past year was 67 days (range 0–365). Primary reasons for use were curiosity, positive drug effect, relaxation, and to get high without having a positive drug test. Acute subjective effects were similar to known effects of cannabis, and a subset of users met DSM criteria for abuse and dependence on Spice products. Conclusions Participants exhibited a diverse profile of use patterns as is typical for other drugs of abuse. There was evidence that users continued to seek and use these drugs after being banned by local authorities. This study should be interpreted with caution due to methodological limitations. Controlled laboratory research is needed to further examine the behavioral pharmacology of individual synthetic cannabinoids found in Spice products.

Gut feelings about the endocannabinoid system

Stemming from the centuries-old and well known effects of Cannabis on intestinal motility and secretion, research on the role of the endocannabinoid system in gut function and dysfunction has received ever increasing attention since the discovery of the cannabinoid receptors and their endogenous ligands, the endocannabinoids. In this article, some of the most recent developments in this field are discussed, with particular emphasis on new data, most of which are published in Neurogastroenterology & Motility, on the potential tonic endocannabinoid control of intestinal motility, the function of cannabinoid type-1 (CB1) receptors in gastric function, visceral pain, inflammation and sepsis, the emerging role of cannabinoid type-2 (CB2) receptors in the gut, and the pharmacology of endocannabinoid-related molecules and plant cannabinoids not necessarily acting via cannabinoid CB1 and CB2 receptors. These novel data highlight the multi-faceted aspects of endocannabinoid function in the GI tract, support the feasibility of the future therapeutic exploitation of this signaling system for the treatment of GI disorders, and leave space for some intriguing new hypotheses on the role of endocannabinoids in the gut.

Structural and pharmacological analysis of O-2050, a putative neutral cannabinoid CB1 receptor antagonist

Rimonabant, the prototypic antagonist of cannabinoid CB1 receptors, has been reported to have inverse agonist properties at higher concentrations, which may complicate its use as a tool for mechanistic evaluation of cannabinoid pharmacology. Consequently, recent synthesis efforts have concentrated on discovery of a neutral antagonist using a variety of structural templates. The purpose of this study was to evaluate the pharmacological properties of the putative neutral cannabinoid CB1 receptor antagonist O-2050, a sulfonamide side chain analog of Δ8-tetrahydrocannabinol. O-2050 and related sulfonamide cannabinoids exhibited good affinity for both cannabinoid CB1 and CB2 receptors. While the other sulfonamide analogs produced cannabinoid agonist effects in vivo (e.g., activity suppression, antinociception, and hypothermia), O-2050 stimulated activity and was inactive in the other two tests. O-2050 also decreased food intake in mice, an effect that was reminiscent of that produced by rimonabant. Unlike rimonabant, however, O-2050 did not block the effects of cannabinoid agonists in vivo, even when administered i.c.v. In contrast, O-2050 antagonized the in vitro effects of cannabinoid agonists in [35S]GTPγS and mouse vas deferens assays without having activity on its own in either assay. Further evaluation revealed that O-2050 fully and dose-dependently substituted for Δ9-tetrahydrocannabinol in a mouse drug discrimination procedure (a cannabinoid agonist effect) and that it inhibited forskolin-stimulated cyclic AMP signaling with a maximum efficacy of approximately half that of the full agonist CP55,940 [(-)-cis-3-[2-hydroxy-4(1,1-dimethyl-heptyl)phenyl]-trans-4-(3-hydroxy-propyl)cyclohexanol]. Together, these results suggest that O-2050 is not a viable candidate for classification as a neutral cannabinoid CB1 receptor antagonist.

How important are sex differences in cannabinoid action?

In humans as in animals, males and females are dissimilar in their genetic and hormonally driven behaviour; they process information differently, perceive experience and emotions in different ways, display diverse attitudes, language and social skills, and show sex-related differences in the brain anatomy and organization. Drug addiction is a widespread relapsing illness that affects both men and women. Sex-dependent differences have been frequently observed in the biological and behavioural effects of substances of abuse, including cannabis. Beside sex differences observed in the cannabinoid-induced effects related to cannabis abuse and dependence, cannabinoids have been shown to exert sex-dependent effects also in other physiological and behavioural aspects, such as food intake and energy balance (more evident in males), or anxiety and depression (more evident in females). Research has just begun to identify factors which could provide a neurobiological basis for gender-based differences in cannabinoid effects, among which, gonadal hormones seem to play a crucial role. Yet, cannabinoid pharmacodynamic and pharmacokinetic may also be important, as sex differences in cannabinoid effects might be due, at least in part, to differences in muscle mass and fat tissue distribution between males and females. Here, we will review both clinical and laboratory-based research evidence revealing important sex-related differences in cannabinoid effects, and put forward some suggestions for future studies to fill the gap in our knowledge of gender-specific bias in cannabinoid pharmacology.

Functional role of cannabinoid receptors in urinary bladder

Cannabinoids, the active components of Cannabis sativa (maijuana), and their derivatives produce a wide spectrum of central and peripheral effects, some of which may have clinical applications. The discovery of specific cannabinoid receptors and a family of endogenous ligands of those receptors has attracted much attention to the general cannabinoid pharmacology. In recent years, studies on the functional role of cannabinoid receptors in bladder have been motivated by the therapeutic effects of cannabinoids on voiding dysfunction in multiple sclerosis patients. In this review, we shall summarize the literature on the expression of cannabinoid receptors in urinary bladder and the peripheral influence of locally and systemically administered cannabinoids in the bladder. The ongoing search for cannabinoid-based therapeutic strategies devoid of psychotropic effects can be complemented with local delivery into bladder by the intravesical route. A greater understanding of the role of the peripheral CB1 and CB2 receptor system in lower urinary tract is necessary to allow the development of new treatment for pelvic disorders.

Discovery and functional evaluation of diverse novel human CB1 receptor ligands

Ligand-based virtual screening with a 3D pharmacophore led to the discovery of 30 novel, diverse and drug-like ligands of the human cannabinoid receptor 1 (hCB1). The pharmacophore was validated with a hit rate of 16%, binding selectivity versus hCB2, and expected functional profiles. The discovered compounds provide new tools for exploring cannabinoid pharmacology.

Selective blockade of 2-arachidonoylglycerol hydrolysis produces cannabinoid behavioral effects

2-Arachidonoylglycerol (2-AG) and anandamide are endocannabinoids that activate cannabinoid receptors CB1 and CB2. Endocannabinoid signaling is terminated by enzymatic hydrolysis, a process that, for anandamide, is mediated by fatty acid amide hydrolase (FAAH) and, for 2-AG, is thought to involve monoacylglycerol lipase (MAGL). FAAH inhibitors produce a select subset of the behavioral effects observed with CB1 agonists, intimating a functional segregation of endocannabinoid signaling pathways in vivo. Testing this hypothesis, however, requires specific tools to independently block anandamide and 2-AG metabolism. Here, we report a potent and selective inhibitor of MAGL, JZL184, that, upon administration to mice, raises brain 2-AG by 8-fold without altering anandamide. JZL184-treated mice exhibited a broad array of CB1-dependent behavioral effects, including analgesia, hypothermia, and hypomotility. These data indicate that 2-AG endogenously modulates several behavioral processes classically associated with the pharmacology of cannabinoids and point to overlapping and unique functions for 2-AG and anandamide in vivo.

Behavioral Pharmacology of Cannabinoids with a Focus on Preclinical Models for Studying Reinforcing and Dependence-Producing Properties

Cannabis preparations as recreational drugs are the most widely used illicit drugs in the world. Although cannabis derivatives produce clear subjective motivational responses in humans leading to drug-seeking behavior and in a specific proportion in repeated drug use, the reinforcing/rewarding attributes of these subjective effects are difficult to define in experimental animals. This led to the notion of cannabinoids being considered as "atypical" or "anomalous" drugs of abuse. To this end, our knowledge and understanding of the way cannabis and its main psychoactive constituent, Delta(9)-tetrahydrocannabinol (Delta(9)-THC), act in the central nervous system to exert their reinforcing/rewarding effects is far from complete. The aim of the present article is to review from a preclinical perspective the current status of what is known about the behavioral pharmacology of cannabinoids including the recently identified cannabinoid neurotransmission modifiers with a particular emphasis on their motivational/reinforcing and dependence-producing properties. We conclude that cannabinoids exhibit reinforcing/rewarding properties in experimental animals mostly under particular experimental conditions, which is not the case for other drugs of abuse, such as opiates, psychostimulants, alcohol and nicotine. The paper will discuss these findings critically and also point to open questions that should be addressed in the future in order to improve our understanding of these specific actions of cannabinoids that will also impact drug discovery and development efforts of related compounds as therapeutics in the clinic.

Pharmacological and therapeutic secrets of plant and brain (endo)cannabinoids

Research on the chemistry and pharmacology of cannabinoids and endocannabinoids has reached enormous proportions, with approximately 15,000 articles on Cannabis sativa L. and cannabinoids and over 2,000 articles on endocannabinoids. The present review deals with the history of the Cannabis sativa L. plant, its uses, constituent compounds and their biogeneses, and similarity to compounds from Radula spp. In addition, details of the pharmacology of natural cannabinoids, as well as synthetic agonists and antagonists are presented. Finally, details regarding the pioneering isolation of the endocannabinoid anandamide, as well as the pharmacology and potential therapeutic uses of endocannabinoid congeners are presented.

Human Cannabinoid Pharmacokinetics

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Human cannabinoid pharmacokinetics.

A multitude of roles for the endogenous cannabinoid system has been proposed by recent research efforts. A large number of endogenous cannabinoid neurotransmitters or endocannabinoids have been identified, and the CB-1 and CB-2 cannabinoid receptors have been characterized. The presence of other receptors, transporters, and enzymes responsible for the synthesis or metabolism of endocannabinoids are becoming known at an extraordinary pace. The complex functions of this novel system have created multiple new targets for pharmacotherapies. Research has focused on separating the behavioral psychoactive effects of cannabinoid agonists from therapeutic effects. These efforts have been largely unsuccessful. Another strategy centers on changing the pharmacokinetics of drug delivery to maximize therapeutic effect and minimize cognitive and subjective drug effects. Development of oral, rectal, and transdermal medications of synthetic Δ9-tetrahydrocannabinol (THC)1) are examples of this type of approach. Additionally, the potential therapeutic benefits of administering unique combinations of cannabinoids and other chemicals present in the plant Cannabis sativa is being investigated by the oromucosal route. There also is strong interest in medications based on antagonizing endocannabinoid action. We have shown that the cardiovascular and subjective effects of cannabis are blocked by rimonabant, the first CB-1 cannabinoid-receptor antagonist, documenting that CB-1 receptors mediate these effects of smoked cannabis in humans. It is clear that the endogenous cannabinoid system plays a critical role in physiological and behavioral processes, and extensive research effort is being devoted to the biology, chemistry, pharmacology, and toxicology of cannabinoids. Cannabis is one of the oldest and most commonly abused drugs in the world, and its use is associated with pathological and behavioral toxicity. Thus, it is important to understand cannabinoid pharmacokinetics and the disposition of cannabinoids into biological fluids and tissues. Understanding the pharmacokinetics of a drug is essential to understanding the onset, magnitude, and duration of its pharmacodynamic effects, maximizing therapeutic and minimizing negative side effects. Cannabinoid pharmacokinetics encompasses absorption after diverse routes of administration and from different drug formulations, analyte distribution throughout the body, metabolism by the liver and extra-hepatic tissues, and elimination in the feces, urine, sweat, oral fluid, and hair. Pharmacokinetic processes are dynamic, may change over time, and may be affected by the frequency and magnitude of drug exposure. The many contributions to our understanding of cannabinoid pharmacokinetics from the 1970s and 1980s are reviewed, and the findings of recent research expanding upon this knowledge are detailed. Cannabinoid pharmacokinetics research is challenging due to low analyte concentrations, rapid and extensive metabolism, and physico-chemical characteristics hindering the separation of drugs of interest from biological matrices and from each other. Drug recovery is reduced due to adsorption of compounds of interest to multiple surfaces. Much of the early cannabinoid data are based on radiolabeled cannabinoids yielding highly sensitive, but less specific, measurement of individual cannabinoid analytes. New extraction techniques and mass-spectrometric (MS) developments now permit highly sensitive and specific measurement of cannabinoids in a wide variety of biological matrices, improving our ability to characterize cannabinoid pharmacokinetics. Cannabis sativa contains over 421 different chemical compounds, including over 60 cannabinoids [1-3]. Cannabinoid plant chemistry is far more complex than that of pure THC, and different effects may be expected due to the presence of additional cannabinoids and other chemicals. Eighteen different classes of chemicals, including nitrogenous compounds, amino acids, hydrocarbons, carbohydrates, terpenes, and simple and fatty acids, contribute to the known pharmacological and toxicological properties of cannabis. THC is usually present in Cannabis plant material as a mixture of monocarboxylic acids, which readily and efficiently decarboxylate upon heating. THC decomposes when exposed to air, heat, or light; exposure to acid can oxidize the compound to cannabinol (CBN), a much less-potent cannabinoid. In addition, cannabis plants dried in the sun release variable amounts of THC through decarboxylation. During smoking, more than 2,000 compounds may be produced by pyrolysis. The pharmacokinetics of THC, the primary psychoactive component of cannabis, its metabolites ‘11-hydroxytetrahydrocannabinol’ (11-OH-THC) and ‘11-nor-9-carboxy-tetrahydrocannabinol’ (THC-COOH)]2), and another cannabinoid present in high concentration, cannabidiol (CBD), a non-psychoactive agent with an interesting array of potential therapeutic indications, are included. Mechoulam et al. elucidated the structure of THC in 1964, enabling studies of the drug's pharmacokinetics [4]. THC, containing no N-atom, but with two stereogenic centers in a trans configuration, has been described by two different atom-numbering systems, either the dibenzopyran (or Δ9) or the monoterpene (or Δ1) system. In this review, the dibenzopyran (Δ9) system is employed.

An Overview on the Biochemistry of the Cannabinoid System

About 40 years ago, cannabinoids were considered as the substances responsible for the psychoactive properties of marijuana and other derivatives of Cannabis sativa, whereas their medicinal use remained unexplored. However, with the discovery of the endocannabinoid system 20 years later, the compounds able to modify this system are being reconsidered for their therapeutic potential. Thus, the term "cannabinoid" includes now much more compounds than those present in C. sativa derivatives, for instance, numerous synthetic cannabinoids obtained by modifications from plant-derived cannabinoids or from the compounds that behave as endogenous ligands for the different cannabinoid receptor types. The term "cannabinoid" should also refer to some prototypes of selective antagonists for these receptors. The explanation for this exponential growth in cannabinoid pharmacology is the discovery and characterization of the endocannabinoid signaling system (receptors, ligands, and inactivation system) which plays a modulatory role mainly in the brain but also in the periphery. The objective of the present review article was to give an overview of the present state-of-the-art of biochemistry of the endocannabinoid system. Other authors in this volume will review their functions in the brain, their alterations in a variety of neurological and psychiatric pathologies, and the proposed therapeutic benefits in these diseases of new cannabinoid-related compounds that improve the pharmacological properties of classic cannabinoids.

Cannabinoid-Based Medicines for Neurological Disorders—Clinical Evidence

Whereas the cannabis plant has a long history of medicinal use, it is only in recent years that a sufficient understanding of the pharmacology of the main plant constituents has allowed for a better understanding of the most rational therapeutic targets. The distribution of cannabinoid receptors, both within the nervous system and without, and the development of pharmacological tools to investigate their function has lead to a substantial increase in efforts to develop cannabinoids as therapeutic agents. Concomitant with these efforts, the understanding of the pharmacology of plant cannabinoids at receptor and other systems distinct from the cannabinoid receptors suggests that the therapeutic applications of plant-derived cannabinoids (and presumably their synthetic derivatives also) may be diverse. This review aims to discuss the clinical evidence investigating the use of medicines derived, directly or indirectly, from plant cannabinoids with special reference to neurological disorders. Published studies suggest that the oral administration of cannabinoids may not be the preferred route of administration and that plant extracts show greater evidence of efficacy than synthetic compounds. One of these, Sativex (GW Pharmaceuticals), was approved as a prescription medicine in Canada in 2005 and is currently under regulatory review in the EU.

Conformational characteristics of the interaction of SR141716A with the CB1 cannabinoid receptor as determined through the use of conformationally constrained analogs

Interest in cannabinoid pharmacology increased dramatically upon the identification of the first cannabinoid receptor (CB1) in 1998 and continues to expand as additional endocannabinoids and cannabinoid receptors are discovered. Using CB1 receptor (CB1R) systems, medicinal chemistry programs began screening libraries searching for cannabinoid ligands, ultimately leading to the discovery of the first potent cannabinoid receptor antagonist, SR141716A (Rimonabant). Its demonstrated efficacy in treating obesity and facilitating smoking cessation, among other impressive pharmacological activities, has furthered the interest in cannabinoid receptor antagonists as therapeutics, such that the number of patents and publications covering this class of compounds continues to grow at an impressive rate. At this time, medicinal chemistry approaches including combinatorial chemistry, conformational constraint, and scaffold hopping are continuing to generate a large number of cannabinoid antagonists. These molecules provide an opportunity to gain insight into the 3-dimensional structure-activity relationships that appear crucial for CB1R-ligand interaction. In particular, studies in which conformational constraints have been imposed on the various pyrazole ring substituents of SR141716A provide a direct opportunity to characterize changes in conformation/conformational freedom within a single class of compounds. While relatively few conformationally constrained molecules have been synthesized to date, the structure-activity information is often more readily interpreted than in studies where entire substituents are replaced. Thus, it is the focus of this mini-review to examine the structural properties of SR141716A, and to use conformationally constrained molecules to illustrate the importance of conformation and conformational freedom to CB1R affinity, selectivity, and efficacy.

Cannabinoid pharmacology: the first 66 years.

Research into the pharmacology of individual cannabinoids that began in the 1940s, several decades after the presence of a cannabinoid was first detected in cannabis, is concisely reviewed. Also described is how this pharmacological research led to the discovery of cannabinoid CB(1) and CB(2) receptors and of endogenous ligands for these receptors, to the development of CB(1)- and CB(2)-selective agonists and antagonists and to the realization that the endogenous cannabinoid system has significant roles in both health and disease, and that drugs which mimic, augment or block the actions of endogenously released cannabinoids must have important therapeutic applications. Some goals for future research are identified.

Cannabinoids

Since the discovery of an endogenous cannabinoid system, research into the pharmacology and therapeutic potential of cannabinoids has steadily increased. Two subtypes of G-protein coupled cannabinoid receptors, CB(1) and CB(1), have been cloned and several putative endogenous ligands (endocannabinoids) have been detected during the past 15 years. The main endocannabinoids are arachidonoyl ethanolamide (anandamide) and 2-arachidonoyl glycerol (2-AG), derivatives of arachidonic acid, that are produced "on demand" by cleavage of membrane lipid precursors. Besides phytocannabinoids of the cannabis plant, modulators of the cannabinoid system comprise synthetic agonists and antagonists at the CB receptors and inhibitors of endocannabinoid degradation. Cannabinoid receptors are distributed in the central nervous system and many peripheral tissues, including immune system, reproductive and gastrointestinal tracts, sympathetic ganglia, endocrine glands, arteries, lung and heart. There is evidence for some non-receptor dependent mechanisms of cannabinoids and for endocannabinoid effects mediated by vanilloid receptors. Properties of CB receptor agonists that are of therapeutic interest include analgesia, muscle relaxation, immunosuppression, anti-inflammation, antiallergic effects, improvement of mood, stimulation of appetite, antiemesis, lowering of intraocular pressure, bronchodilation, neuroprotection and antineoplastic effects. The current main focus of clinical research is their efficacy in chronic pain and neurological disorders. CB receptor antagonists are under investigation for medical use in obesity and nicotine addiction. Additional potential was proposed for the treatment of alcohol and heroine dependency, schizophrenia, conditions with lowered blood pressure, Parkinson's disease and memory impairment in Alzheimer's disease.