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المستخلص
In the course of its long but fragmented history, the public debate on cannabis during 1980s appears to be entering a dormant phase. In the 1990s the interest in cannabis has grown due its wide spread use in different forms.
The most common route of administration is in a water pipe followed by smoking in cigarettes. Nearly 93% smoke the flowering heads of the plant. Also, others use cannabis by means of chewing or sometimes mixed with other psychoactive drugs. Another method is a beverage, which is made from an infusion of cannabis leaves and flowering tops combined with milk and nuts and is consumed through drinking.
Herbal cannabis contains over 400 compounds including over 60 cannabinoids. The pharmacology of most of the cannabinoids is largely unknown but the most potent psychoactive agent, 9-tetrahydrocannabinol ( 9-THC, or THC), has been isolated, synthesized and much studied. Other plant cannabinoids include 8-THC, cannabinol and cannabidiol. These and other cannabinoids have additive, synergistic or antagonistic effects with THC and may modify its actions when herbal cannabis is smoked. Synthetic cannabinoids such as nabilone and others are also available for therapeutic and research purposes.
The latter half of the twentieth century witnessed a dramatic increase in the availability and use of cannabis throughout world. In 1991, it was declared that cannabis is the most widely used substance all over the world.
By most estimates, cannabis remains the world’s most commonly used illicit drug, with approximately 200 to 300 million regular users. It occupies the 4th place in worldwide popularity among psychoactive drugs, after caffeine, nicotine & alcohol. About one third (31%) of the population were reported to have used cannabis once or more times in their lifetime, 8% had used it in the past year and 5% had used it in the past month. In Egypt, cannabis resin is the favorite drug of Egyptian addicts and the one most widely abused. The prevalence of cannabis in Egypt nowadays is very difficult to assess because of unavailability of regular reports and epidemiological surveys.
Studies showed that there was an 8-fold increased risk of drug disorders among the relatives of probands. Common factors that correlate to cannabis use were peer influence, self-reported poor mental health, availability of cannabis, ignorance of cannabis harm and lack of parental/guardian supervision due to absence of one of the parents, their travel or their loose supervision. There was also a significant positive relationship between cannabis use and a polygamous family background and when the parents belonged to an older age group.
Cannabinoids derived from herbal cannabis interact with endogenous cannabinoid systems in the body. Actions on specific brain receptors cause dose-related impairments of psychomotor performance with implications for car and train driving, aeroplane piloting and academic performance. Other constituents of cannabis smoke carry respiratory and cardiovascular health risks similar to those of tobacco smoke.
Many studies show that cannabis use decreases blood levels of male hormone testosterone, which is necessary for the development and maintenance of the male sexual system. Mice exposed to cannabinoids experience a decrease in sperm count. Cannabis use has also been linked to a decrease in the amount of Luteinizing hormone releasing hormone (LHRH) in the blood. In a frequent cannabis user, THC and other cannabinoids are stored in body fat and released slowly over time. This slow release could lead to a long term effect on fertility and sexual functions due to decrease sperm cell contents and motility.
Heavy cannabis use can precipitate financial problems in two ways. First, drugs themselves cost money. A second source of financial problems is unemployment or job loss. Eventually, continued drug use undermines the person’s energy, ambition, concentration, problem-solving abilities, performance, productivity and social skills in dealing with co-workers and supervisors. Theft from other family members (to obtain drugs) and lying (to hide drug use) undermine the trust necessary for coexistence within the family. Angry outbursts, property destruction and interfamily violence can ensue. Alienation of the drug user from the family once present, is difficult to repair.
Studies examining the relationship between cannabis use and homicide found that in terms of lifetime use, cannabis was the most commonly used illicit drug. About one-third of cannabis users used the drug in the 24-hour period before the homicide; and almost three-quarters of those respondents were experiencing some type of effect from the drug when the homicide occurred. Seven percent of the total sample said that the homicide was related to their cannabis use.
Cannabis withdrawal should be considered a true withdrawal syndrome. Cannabis abstinence effects occur reliably, are not rare, have a well defined time course, abate with readministration of cannabis or THC, and are due to deprivation of a specific substance (THC). A recent study reported that the core symptoms of cannabis withdrawal were anxiety/nervousness, decreased appetite/weight loss, restlessness, sleep difficulties including strange dreams, chills, depressed mood, stomach pains/physical discomfort, shakiness, and sweating.
The one remaining important attribute is clinical importance, which until lately has been unclear. In fact, lack of evidence of clinical importance is cited as the reason for the omission of cannabis withdrawal from the DSM-IV. Recent data support the clinical importance of the syndrome.
Various lines of evidence suggest an association between cannabis and psychosis. These include case reports of cannabis use preceding onset of schizophrenia, psychosis in community surveys of cannabis users, and observational studies of psychosis in cannabis users. The nature of this association is widely debated. Some authors contend that it may be due to socioeconomic and demographic factors common to both substance use and schizophrenia. Other studies suggest that there may be a shared aetiology for substance abuse and schizophrenia, such as common genetic factors or dysregulation of neural circuitry mediating drug reward and reinforcement.
The vulnerability hypothesis postulates that the use of cannabis actually increases the risk of schizophrenia. Support for this vulnerability hypothesis comes from a variety of sources. There is good evidence that cannabis intoxication may lead to brief psychotic episodes or recurrence of psychotic symptoms in individuals with a history of psychosis.
Cannabis use during adolescence or early adult life may be one of a number of environmental stressors that interact with genetic factors to predispose an individual to later psychotic illness. Studies showed that early exposure to cannabis may increase the risk of developing psychiatric problems.
The finding of elevated endogenous cannabinoids (anandamide and palmitylethanolamide) in the cerebrospinal fluid of patients with schizophrenia, independent of gender, age or current medication raises the possibility that the endocannabinoid system may indeed have an aetiological role in schizophrenia. On the other hand, a higher consumption of cannabis by psychotic patients is observed as an attempt to relieve distressing symptoms of their illness or the adverse side-effects of antipsychotic medications.
Cannabis abuse, particularly if heavy, was associated with worsening of psychosis; indeed, many of the abusers reported an increase in their psychotic symptoms soon after taking cannabis. Studies found changed perception, thought insertion, nonverbal auditory hallucinations, delusions of control and delusions of grandiose ability significantly more frequently in cannabis-positive patients with psychotic symptoms than in drug-free psychotic controls.
Cannabis and psychoactive cannabinoids can cause psychotic symptoms of short duration (i.e. a transient psychotic reaction), trigger schizophrenic psychosis (by functioning as an additional or even essential stress factor within the vulnerability/stress coping model), intensify psychotic symptoms and influence the course of schizophrenic disorders, the role of the endogenous cannabinoid system in the pathogenesis of schizophrenic and schizophrenia-like psychoses is not fully understood.
Tetrahydrocannabinol and nabilone are effective anti-emetics but there are no comparisons with 5-HT3 antagonists, so a role in modern anti-emetic regimes remains to be determined. Currently, only nabilone is licensed in the UK and available for prescription and research. THC has recently been rescheduled to permit prescription but remains unlicensed and must be specially imported on a named-patient basis. Delta-8-THC looks worthy of further investigation, particularly in children, and is much simpler to synthesise than THC.
Many individuals with MS have claimed a benefit from cannabis and small controlled trials support this, although effect upon posture and balance requires clarification. THC is an effective analgesic at the expense of sedation with larger doses and may have special merit in neuropathic pain.
No conclusions are possible as yet about anticonvulsant potential. Some cannabinoids reduce IOP, though side-effects of products currently available limit application and effects of tolerance are uncertain. The mechanism for bronchodilation probably differs from that of ß2-stimulants, so synergistic combinations may be possible.
Cannabis and THC are effective appetite stimulants. Alongside anti-emetic, analgesic, anxiolytic, hypnotic and anti-pyretic properties this suggests a unique role in alleviating symptoms in selected patients with cancer or AIDS. This is a compelling area for future research, although possible effects upon immune function require careful monitoring.
Optimal doses and routes of delivery have not been established. Absorption by the oral route is unreliable. Smoking the drug is generally not a viable option since advantages such as rapid onset, accurate titration of effects and reliability in patients who are vomiting have to be set against the likelihood of lung irritation or damage, and it would in any case be unacceptable to most patients. Sublingual sprays or tablets, nebulisers and aerosols look promising for the future, and THC is effective by the rectal route. Many potentially active cannabinoids have yet to be investigated and the recent identification of a peripheral receptor may lead to new drugs devoid of central nervous system effects. Yet the known adverse effects of oral cannabinoids are rarely intolerable or life-threatening, in contrast to those associated with some standard therapies. A British Medical Association survey indicated that many UK doctors believe that cannabis should once again be available on prescription.