Cannabis, commonly known as marijuana[4] and by numerous other names,a[›] is apreparation of the cannabis plant intended for use as a psychoactive drug and asmedicine.[5][6] Pharmacologically, the principal psychoactive constituent of cannabis istetrahydrocannabinol (THC); it is one of 483 known compounds in the plant,[7] including at least 84 other cannabinoids, such as cannabidiol (CBD), cannabinol (CBN),tetrahydrocannabivarin (THCV),[8][9] and cannabigerol (CBG).
Cannabis is often consumed for its psychoactive and physiological effects, which can include heightened mood or euphoria, relaxation,[10] and an increase in appetite.[11]Unwanted side-effects can sometimes include a decrease in short-term memory, dry mouth, impaired motor skills, reddening of the eyes,[10] and feelings of paranoia or anxiety.[12]
Contemporary uses of cannabis are as a recreational or medicinal drug, and as part ofreligious or spiritual rites; the earliest recorded uses date from the 3rd millennium BC.[13]Since the early 20th century cannabis has been subject to legal restrictions with thepossession, use, and sale of cannabis preparations containing psychoactive cannabinoids currently illegal in most countries of the world; the United Nations has said that cannabis is the most-used illicit drug in the world.[14][15] In 2004, the United Nations estimated that global consumption of cannabis indicated that approximately 4% of the adult world population (162 million people) used cannabis annually, and that approximately 0.6% (22.5 million) of people used cannabis daily.[16]
Effects Cannabis has psychoactive and physiological effects when consumed.[17] The immediate desired effects from consuming cannabis include relaxation and mild euphoria (the "high" or "stoned" feeling), while some immediate undesired side-effects include a decrease in short-term memory, dry mouth, impaired motor skills and reddening of the eyes.[18] Aside from a subjective change in perception and mood, the most common short-term physical and neurological effects include increased heart rate, increased appetite and consumption of food, lowered blood pressure, impairment of short-term and working memory,[19][20] psychomotor coordination, and concentration.
A 2013 literature review said that exposure to marijuana had biologically-based physical, mental, behavioral and social health consequences and was "associated with diseases of the liver (particularly with co-existing hepatitis C), lungs, heart, and vasculature".[21]
Cannabis has been used to reduce nausea and vomiting in chemotherapy and people with AIDS, and to treat pain and muscle spasticity.[22] According to a 2013 review, "Safety concerns regarding cannabis include the increased risk of developing schizophrenia with adolescent use, impairments in memory and cognition, accidental pediatric ingestions, and lack of safety packaging for medical cannabis formulations."[22]
The medicinal value of cannabis is disputed. The American Society of Addiction Medicinedismisses the concept of medical cannabis because the plant fails to meet its standard requirements for approved medicines. The US Food and Drug Administration (FDA) maintains that the herb cannabis is associated with numerous harmful health effects, and that significant aspects such as content, production, and supply are unregulated. The FDA approve of the prescription of two products (not for smoking) that have pure THC in a small controlled dose as the active substance.[23][24]
Neurological
A 2013 review comparing different structural and functional imaging studies showed morphological brain alterations in long-term cannabis users which were found to possibly correlate to cannabis exposure.[25] A 2010 review found resting blood flow to be lower globally and in prefrontal areas of the brain in cannabis users, when compared to non-users. It was also shown that giving THC or cannabis correlated with increased bloodflow in these areas, and facilitated activation of the anterior cingulate cortex and frontal cortex when participants were presented with assignments demanding use of cognitive capacity.[26] Both reviews noted that some of the studies that they examined had methodological limitations, for example small sample sizes or not distinguishing adequately between cannabis and alcohol consumption.[25][26]
Gateway drug
Further information: Gateway drug theory
Since the 1950s, United States drug policy has been guided by the assertion that cannabis use increases the probability of trying "harder" drugs.[27] The hypothesis has endured as one of the central pillars of anti-cannabis drug policy in the United States,[28] and as such the validity and implications of the hypothesis are hotly debated.[27] Almost two-thirds of the poly drug users in the "2009/10 Scottish Crime and Justice Survey" used cannabis.[29]
Some studies state that while there is no proof for the gateway hypothesis,[30] young cannabis users should still be considered as a risk group for intervention programs,[31] while other findings indicate that hard drug users are likely to be poly-drug users, and that interventions must address the use of multiple drugs instead of a single hard drug.[32]
Another gateway hypothesis covers that a gateway effect may be caused by the "common factors" involved in using any illegal drug. Through the illegal status of cannabis, users are more likely to be subjected to situations allowing them to acquaint with individuals using or selling various illegal drugs.[33][34] Utilizing this argument some studies have shown that alcohol and tobacco may additionally be regarded as gateway drugs;[35] however, a more parsimonious explanation could be that cannabis is simply more readily available (and at an earlier age) than illegal hard drugs. In turn alcohol and tobacco are easier to obtain at an earlier point than is cannabis (though the reverse may be true in some areas), thus leading to the "gateway sequence" in those individuals since they are most likely to experiment with any drug offered.[27]
Jacob Sullum analyzed the "gateway" theory in a 2003 Reason magazine article, noting that the theory's "...durability is largely due to its ambiguity: Because it's rarely clear what people mean when they say that pot smoking leads to the use of "harder" drugs, the claim is difficult to disprove.":
- "Notice that none of these interpretations involves a specific pharmacological effect of the sort drug warriors seem to have in mind when they suggest that pot smoking primes the brain for cocaine or heroin. As a National Academy of Sciences panel observed in a 1999 report, 'There is no evidence that marijuana serves as a stepping stone on the basis of its particular drug effect.' Last year the Canadian Senate's Special Committee on Illegal Drugs likewise concluded that 'cannabis itself is not a cause of other drug use. In this sense, we reject the gateway theory.'"[36]
Safety
Further information: Cannabis in pregnancy
Fatal overdoses associated with cannabis use have not been reported as of 2008.[37] There has been too little research to determine whether cannabis users die at a higher rate as compared to the general population, though some studies suggest that fatal motor vehicle accidents and death from respiratory and brain cancers may be more frequent among heavy cannabis users. It is not clear whether cannabis use affects the rate of suicide.[37]
THC, the principal psychoactive constituent of the cannabis plant, has low toxicity, the dose of THC needed to kill 50% of tested rodents is very high,[38] and human deaths from overdose are extremely rare.[39]
Evaluations of safety and tolerability of Sativex, a pharmacological preparation made from cannabinoids, have concluded that it is indeed well-tolerated and, in one class of patients, useful.[40]
Many studies have looked at the effects of smoking cannabis on the respiratory system. Cannabis smoke contains thousands of organic and inorganic chemical compounds. This tar is chemically similar to that found in tobacco smoke,[41] and over fifty known carcinogens have been identified in cannabis smoke,[42] including; nitrosamines, reactive aldehydes, and polycylic hydrocarbons, including benz[a]pyrene.[43]
There is serious suspicion among cardiologists, spurring research but falling short of definitive proof, that cannabis use has the potential to contribute to cardiovascular disease. Cannabis is believed to be an aggravating factor in rare cases of arteritis, a serious condition that in some cases leads to amputation. Because 97% of case-reports also smoked tobacco, a formal association with cannabis could not be made. If cannabis arteritis turns out to be a distinct clinical entity, it might be the consequence of vasoconstrictor activity observed from delta-8-THCand delta-9-THC.[44] Other serious cardiovascular events including myocardial infarction, stroke, sudden cardiac death, and cardiomyopathyhave been reported to be temporally associated with cannabis use. Research in these events is complicated because cannabis is often used in conjunction with tobacco, and drugs such as alcohol and cocaine.[45] These putative effects can be taken in context of a wide range of cardiovascular phenomena regulated by the endocannabinoid system and an overall role of cannabis in causing decreased peripheral resistance and increased cardiac output, which potentially could pose a threat to those with cardiovascular disease.[46]
Varieties and strains
Cannabis indica may have a CBD:THC ratio four to five times that of Cannabis sativa. Cannabis strains with relatively high CBD:THC ratios are less likely to induce anxiety than those with a lower ratio. This may be due to CBD's antagonistic effects at the cannabinoid receptors, compared to THC'spartial agonist effect. CBD is also a 5-HT1A receptor agonist, which may also contribute to an anxiolytic effect.[47] This likely means the high concentrations of CBD found in Cannabis indicamitigate the anxiogenic effect of THC significantly.[47] The effects of sativa are well known for their cerebral high, hence its daytime use as medical cannabis, while indica is well known for its sedative effects and preferred night time use as medical cannabis.[47]
Concentration of psychoactive ingredients
According to the United Nations Office on Drugs and Crime (UNODC), "the amount of THC present in a cannabis sample is generally used as a measure of cannabis potency."[48] The three main forms of cannabis products are the flower, resin (hashish), and oil (hash oil). The UNODC states that cannabis often contains 5% THC content, resin "can contain up to 20% THC content", and that "Cannabis oil may contain more than 60% THC content."[48]
A scientific study published in 2000 in the Journal of Forensic Sciences (JFS) found that the potency (THC content) of confiscated cannabis in the United States (US) rose from "approximately 3.3% in 1983 and 1984", to "4.47% in 1997". The study also concluded that "other major cannabinoids (i.e., CBD, CBN, and CBC)" (other chemicals in cannabis) "showed no significant change in their concentration over the years".[49] More recent research undertaken at the University of Mississippi's Potency Monitoring Project found that average THC levels in cannabis samples between 1975 and 2007 steadily increased,[50] for example THC levels in 1985 averaged 3.48% by 2006 this had increased to an average of 8.77%.[50]
Australia's National Cannabis Prevention and Information Centre (NCPIC) states that the buds (flowers) of the female cannabis plant contain the highest concentration of THC, followed by the leaves. The stalks and seeds have "much lower THC levels".[51] The UN states that leaves can contain ten times less THC than the buds, and the stalks one hundred times less THC.[48]
After revisions to cannabis rescheduling in the UK, the government moved cannabis back from a class C to a class B drug. A purported reason was the appearance of high potency cannabis. They believe skunk accounts for between 70 and 80% of samples seized by police[52] (despite the fact that skunk can sometimes be incorrectly mistaken for all types of herbal cannabis).[53][54] Extracts such as hashish and hash oiltypically contain more THC than high potency cannabis flowers.
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