Cannabis and cannabinoid receptors.

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Abstract

“Cannabis and cannabinoids exert many of their biological functions through receptor-mediated mechanisms. Two types of cannabinoid receptors have been identified, namely CB(1) and CB(2), both coupled to a G protein. CB(1) receptors have been detected in the central nervous system (where they are responsible for the characteristic effects of Cannabis, including catalepsy, depression of motor activity, analgesia and feelings of relaxation and well being) and in peripheral neurons (where their activation produces a suppression in neurotransmitter release in the heart, bladder, intestine and vas deferens). Cannabinoid CB(2) receptors have only been detected outside the central nervous system, mostly in cells of the immune system, presumably mediating cannabinoid-induced immunosuppression and antinflammatory effects. With the discovery of cannabinoid receptors for exogenous cannabinoids, also endogenous cannabinoids (anandamide, 2-arachidonylglycerol) have been described.”

http://www.ncbi.nlm.nih.gov/pubmed/10930707

CB₁-independent mechanisms of Δ⁹-THCV, AM251 and SR141716 (rimonabant).

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Abstract

“WHAT IS KNOWN AND OBJECTIVE:

The potential beneficial therapeutic effects of cannabinoid CB₁ receptor antagonists or partial agonists have driven drug discovery and development efforts and have led to clinical candidates. It is generally assumed that these compounds are CB₁ ‘selective’ and produce their effects exclusively via CB₁ receptors.

METHODS:

A literature search was conducted of preclinical publications containing information about non-CB₁ receptor pharmacology of these agents. The information was summarized and evaluated from the perspective of contribution to a fuller understanding of this aspect of these compounds.

RESULTS AND DISCUSSION:

A number of recent studies have revealed that these compounds have CB₁-independent pharmacological actions. We highlight the evidence regarding effects produced in cells lacking CB₁ receptors, effects on neuronal membranes from CB₁ receptor-deficient mutant KO ‘knockout’ mice and affinity for μ-opioid receptors.

WHAT IS NEW AND CONCLUSION:

CB₁ ‘selective’ antagonists and partial agonists have been studied for their anorexigenic and other potential therapeutic uses. An awareness of CB₁-independent mechanism(s) of these agents might contribute to a better understanding of the pharmacologic and toxicologic profiles of these agents.”

http://www.ncbi.nlm.nih.gov/pubmed/21740450

Cannabis reinforcement and dependence: role of the cannabinoid CB1 receptor.

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Abstract

“Awareness of cannabis dependence as a clinically relevant issue has grown in recent years. Clinical and laboratory studies demonstrate that chronic marijuana smokers can experience withdrawal symptoms upon cessation of marijuana smoking and have difficulty abstaining from marijuana use. This paper will review data implicating the cannabinoid CB1 receptor in regulating the behavioral effects of Δ9-tetrahydrocannobinol (THC), the primary psycho-active component of cannabis, across a range of species. The behavioral effects that will be discussed include those that directly contribute to the maintenance of chronic marijuana smoking, such as reward, subjective effects, and the positive and negative reinforcing effects of marijuana, THC and synthetic cannabinoids. The role of the CB1 receptor in the development of marijuana dependence and expression of withdrawal will also be discussed. Lastly, treatment options that may alleviate withdrawal symptoms and promote marijuana abstinence will be considered.”

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2731704/

Dronabinol for the Treatment of Cannabis Dependence: A Randomized, Double-Blind, Placebo-Controlled Trial

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   “The purpose of this study was to evaluate the safety and efficacy of dronabinol, a synthetic form of delta-9-tetrahydrocannabinol, a naturally occurring pharmacologically active component of marijuana, in treating cannabis dependence… This is the first trial using an agonist substitution strategy for treatment of cannabis dependence. Dronabinol showed promise, it was well-tolerated, and improved treatment retention and withdrawal symptoms. Future trials might test higher doses, combinations of dronabinol with other medications with complementary mechanisms, or with more potent behavioral interventions.

The agonist substitution strategy has been effective for other substance use disorders, mainly nicotine (nicotine patch, other nicotine replacement products, varenicline) and opioid dependence (methadone, buprenorphine). Therefore, dronabinol, an orally bioavailable synthetic form of delta-9-tetrahydrocannabinol (THC), the main psychoactive component of marijuana acting at the cannabinoid 1 (CB1) receptor, seems a logical candidate medication for cannabis dependence. An ideal agonist medication has low abuse potential, reduces withdrawal symptoms and craving, and decreases the reinforcing effects of the target drug, thereby facilitating abstinence. Dronabinol has been shown to reduce cannabis withdrawal symptoms in laboratory settings among non-treatment seeking cannabis users. Although dronabinol produced modest positive subjective effects among cannabis users in the laboratory, there is little evidence of abuse or diversion of dronabinol in community settings. We conducted a randomized, placebo-controlled trial to evaluate the safety and efficacy of dronabinol for patients seeking treatment for cannabis dependence. This is, to our knowledge, the largest clinical trial to date to evaluate a pharmacologic intervention for cannabis dependence, and the first to attempt agonist substitution.

.In conclusion, agonist substitution pharmacotherapy with dronabinol, a synthetic form of THC, showed promise for treatment of cannabis dependence, reducing withdrawal symptoms and improving retention in treatment, although it failed to improve abstinence. The trial showed that among adult cannabis-dependent patients, dronabinol was well accepted, with good adherence and few adverse events. Future studies should consider testing higher doses of dronabinol, with longer trial lengths, combining dronabinol with other medications acting through complementary mechanisms or more potent behavioral interventions. Moreover, the field should particularly seek to develop high affinity CB1 partial agonists.”

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3154755/

Marijuana Withdrawal in Humans: Effects of Oral THC or Divalproex

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   “Abstinence following daily marijuana use can produce a withdrawal syndrome characterized by negative mood (eg irritability, anxiety, misery), muscle pain, chills, and decreased food intake. Two placebo-controlled, within-subject studies investigated the effects of a cannabinoid agonist, delta-9-tetrahydrocannabinol (THC: Study 1), and a mood stabilizer, divalproex (Study 2), on symptoms of marijuana withdrawal. Participants (n=7/study), who were not seeking treatment for their marijuana use, reported smoking 6–10 marijuana cigarettes/day, 6–7 days/week. Study 1 was a 15-day in-patient, 5-day outpatient, 15-day in-patient design. During the in-patient phases, participants took oral THC capsules (0, 10 mg) five times/day, 1 h prior to smoking marijuana (0.00, 3.04% THC). Active and placebo marijuana were smoked on in-patient days 1–8, while only placebo marijuana was smoked on days 9–14, that is, marijuana abstinence. Placebo THC was administered each day, except during one of the abstinence phases (days 9–14), when active THC was given. Mood, psychomotor task performance, food intake, and sleep were measured. Oral THC administered during marijuana abstinence decreased ratings of ‘anxious’, ‘miserable’, ‘trouble sleeping’, ‘chills’, and marijuana craving, and reversed large decreases in food intake as compared to placebo, while producing no intoxication. Study 2 was a 58-day, outpatient/in-patient design. Participants were maintained on each divalproex dose (0, 1500 mg/day) for 29 days each. Each maintenance condition began with a 14-day outpatient phase for medication induction or clearance and continued with a 15-day in-patient phase. Divalproex decreased marijuana craving during abstinence, yet increased ratings of ‘anxious’, ‘irritable’, ‘bad effect’, and ‘tired.’ Divalproex worsened performance on psychomotor tasks, and increased food intake regardless of marijuana condition. Thus, oral THC decreased marijuana craving and withdrawal symptoms at a dose that was subjectively indistinguishable from placebo. Divalproex worsened mood and cognitive performance during marijuana abstinence. These data suggest that oral THC, but not divalproex, may be useful in the treatment of marijuana dependence.

To conclude, there are currently no effective pharmacotherapies for cannabinoid dependence, yet the large number of nonresponders in marijuana treatment studies emphasizes the importance of increasing treatment options for marijuana dependence. We have developed a laboratory model to predict medications that may show promise clinically for the treatment of marijuana dependence. The present findings, in combination with earlier studies, suggest that nefazodone and oral THC show promise as potential treatment medications, while bupropion and divalproex do not…”

http://www.nature.com/npp/journal/v29/n1/full/1300310a.html

The cannabis withdrawal syndrome.

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Abstract

“PURPOSE OF REVIEW:

The demand for treatment for cannabis dependence has grown dramatically. The majority of the people who enter the treatment have difficulty in achieving and maintaining abstinence from cannabis. Understanding the impact of cannabis withdrawal syndrome on quit attempts is of obvious importance. Cannabis, however, has long been considered a ‘soft’ drug, and many continue to question whether one can truly become dependent on cannabis. Skepticism is typically focused on whether cannabis use can result in ‘physiological’ dependence or withdrawal, and whether withdrawal is of clinical importance.

RECENT FINDINGS:

The neurobiological basis for cannabis withdrawal has been established via discovery of an endogenous cannabinoid system, identification of cannabinoid receptors, and demonstrations of precipitated withdrawal with cannabinoid receptor antagonists. Laboratory studies have established the reliability, validity, and time course of a cannabis withdrawal syndrome and have begun to explore the effect of various medications on such withdrawal. Reports from clinical samples indicate that the syndrome is common among treatment seekers.

SUMMARY:

A clinically important withdrawal syndrome associated with cannabis dependence has been established. Additional research must determine how cannabis withdrawal affects cessation attempts and the best way to treat its symptoms.”

http://www.ncbi.nlm.nih.gov/pubmed/16612207

Adverse effects of cannabis. (2011)

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Abstract

“Cannabis, Cannabis sativa L., is used to produce a resin that contains high levels of cannabinoids, particularly delta9-tetrahydrocannabinol (THC), which are psychoactive substances. Although cannabis use is illegal in France and in many other countries, it is widely used for its relaxing or euphoric effects, especially by adolescents and young adults. What are the adverse effects of cannabis on health? During consumption? And in the long term? Does cannabis predispose users to the development of psychotic disorders? To answer these questions, we reviewed the available evidence using the standard Prescrire methodology. The long-term adverse effects of cannabis are difficult to evaluate. Since and associated substances, with or without the user’s knowledge. Tobacco and alcohol consumption, and particular lifestyles and behaviours are often associated with cannabis use. Some traits predispose individuals to the use of psychoactive substances in general. The effects of cannabis are dosedependent.The most frequently report-ed adverse effects are mental slowness, impaired reaction times, and sometimes accentuation of anxiety. Serious psychological disorders have been reported with high levels of intoxication. The relationship between poor school performance and early, regular, and frequent cannabis use seems to be a vicious circle, in which each sustains the other. Many studies have focused on the long-term effects of cannabis on memory, but their results have been inconclusive. There do not * About fifteen longitudinal cohort studies that examined the influence of cannabis on depressive thoughts or suicidal ideation have yielded conflicting results and are inconclusive. Several longitudinal cohort studies have shown a statistical association between psychotic illness and self-reported cannabis use. However, the results are difficult to interpret due to methodological problems, particularly the unknown reliability of self-reported data. It has not been possible to establish a causal relationship in either direction, because of these methodological limitations. In Australia, the marked increase in cannabis use has not been accompanied by an increased incidence of schizophrenia. On the basis of the available data, we cannot reach firm conclusions on whether or not cannabis use causes psychosis. It seems prudent to inform apparently vulnerable individuals that cannabis may cause acute psychotic decompensation, especially at high doses. Users can feel dependent on cannabis, but this dependence is usually psychological. Withdrawal symptoms tend to occur within 48 hours following cessation of regular cannabis use, and include increased irritability, anxiety, nervousness, restlessness, sleep difficulties and aggression. Symptoms subside within 2 to 12 weeks. Driving under the influence of cannabis doubles the risk of causing a fatal road accident. Alcohol consumption plays an even greater role. A few studies and a number of isolated reports suggest that cannabis has a role in the occurrence of cardiovascular adverse effects, especially in patients with coronary heart disease. Numerous case-control studies have investigated the role of cannabis in the incidence of some types of cancer. Its role has not been ruled out, but it is not possible to determine whether the risk is distinct from that of the tobacco with which it is often smoked. Studies that have examined the influence of cannabis use on the clinical course of hepatitis C are inconclusive. Alcohol remains the main toxic agent that hepatitis C patients should avoid. In practice, the adverse effects of low-level, recreational cannabis use are generally minor, although they can apparently be serious in vulnerable individuals. The adverse effects of cannabis appear overall to be less serious than those of alcohol, in terms of neuropsychological and somatic effects, accidents and violence.”

http://www.ncbi.nlm.nih.gov/pubmed/21462790

Cannabis–1988.

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Abstract

“In this updating review of research on cannabis particular attention has been paid to the increasing number of studies of the disposition of the components of cannabis in man, as well as possible effects on health. Specific binding sites for cannaboids have not been demonstrated. Approximately 80 metabolites of tetrahydrocannabiol (THC) have been discovered, of which 11-OH-THC is the main metabolite, but it contributes little to the overall effect when the drug is smoked or given intravenously. The minimum plasma level of THC associated with the psychotropic effect is 25 ng/ml. Cannabis may produce directly an acute panic reaction, a toxic delirium, and acute paranoid state, or acute mania. Cannabis use may aggrevate schizophrenia, but it is much less certain whether it can lead to sociopathy or even to “amotivational syndrome”. Despite widespread use of cannabis in virtually all parts of the world, no catastrophic effects on health have been noted. Cannabis appears to be relatively safe as compared with current social drugs. It is, however, still too early in the history of the present episode of cannabis use to be sanguine about possible bad effects.”

http://www.ncbi.nlm.nih.gov/pubmed/2852450

Reinforcing properties of oral delta 9-tetrahydrocannabinol, smoked marijuana, and nabilone: influence of previous marijuana use.

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Abstract

“The reinforcing properties of delta 9THC (17.5 mg), a 1 g marijuana cigarette containing 1.83% delta 9-THC, a synthetic cannabis compound (Nabilone 2 mg orally), and their respective placebos were assessed with self-report and operant work-contingent choice procedures. Three groups of eight subjects were selected on the basis of a history of regular, intermittent, or occasional marijuana-smoking behavior. All subjects served as their own controls for each drug condition and studies were carried out under double-blind and “double-dummy” conditions in a controlled, residential research ward. Placebo responding did not vary as a function of history of marijuana use, but the past history of drug use had a significant influence on the reinforcing properties of cannabis compounds as well as the behavioral and physiological effects of these drugs. Regular marijuana users reported a significant increase in elation following marijuana smoking, but this was not associated with a significant increment in pulse rate. Intermittent and occasional marijuana smokers had significant increases in pulse rate, but no significant marijuana-induced elation. Nabilone and delta 9-THC produced a significant increase in pulse rate for all subject groups, but there was no significant increase in elation following ingestion of these compounds. Given a choice between the three drugs and three placebos, 18 of 23 subjects worked to obtain a marijuana cigarette in an operant work choice paradigm. These data indicate that smoked marijuana was significantly more reinforcing than all other cannabis compounds studied, regardless of past drug-use history.”

http://www.ncbi.nlm.nih.gov/pubmed/6149589

Reinforcing and subjective effects of oral delta 9-THC and smoked marijuana in humans.

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Abstract

“The reinforcing and subjective effects of oral delta-9-tetrahydrocannabinol (THC) and smoked marijuana were studied in two groups of regular marijuana users. One group (N = 10) was tested with smoked marijuana and the other (N = 11) with oral THC. Reinforcing effects were measured with a discrete-trial choice procedure which allowed subjects to choose between the self-administration of active drug or placebo on two independent occasions. Subjective effects and heart rate were measured before and after drug administration. Smoked active marijuana was chosen over placebo on both choice occasions by all subjects. Similarly, oral THC was chosen over placebo on both occasions by all but one subject. Both active drug treatments produced qualitatively and quantitatively similar subjective effects, and both significantly increased heart rate, although the time course of effects differed substantially between the two treatments. The results demonstrate that both smoked marijuana and oral THC can serve as positive reinforcers in human subjects under laboratory conditions. The experimental paradigm used here should prove useful for identifying factors that influence the self-administration of marijuana and other cannabinoids by humans.”

http://www.ncbi.nlm.nih.gov/pubmed/1319601