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Реферат: Marijuana In Detail Essay Research Paper

Название: Marijuana In Detail Essay Research Paper
Раздел: Топики по английскому языку
Тип: реферат Добавлен 03:56:51 04 ноября 2010 Похожие работы
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Marijuana In Detail Essay, Research Paper

"Marijuana causes long-term changes in the brain similar to those seen with

other drugs of abuse . . ." Back in the 1970s, animal experiments led to

groundless fears that marijuana blew holes in brain tissue. The experiments

organisations like NIDA now fund are more sophisticated but the controversy

still rages. George Koob, an addiction researcher from The Scripps Research

Institute in La Jolla, California, claims the new message from the animals is

simple: "The more we discover about the neurobiology of addiction the more

common elements we’re seeing between THC (tetrahydrocannabinol, the main active

ingredient in cannabis) and other drugs of abuse." And for Koob, one of

these newly discovered "common elements" is marijauna’s ability to

trigger chemical changes in the brain that lead to strong withdrawal symptoms.

In humans, some researchers claim to see clear evidence of insomnia, anxiety and

even flu-like symptoms in heavy cannabis users who abstain. But if there’s a

consensus, it’s that symptoms are mild and variable. By contrast, Koob’s rats

are shivering wrecks. Does this mean marijuana is more addictive than we think?

Not a bit of it, says Roger Pertwee, a university pharmacologist and president

of the Cannabinoid Research Society. That’s because those symptoms aren’t so

much observed as manufactured. The animals are injected with high doses of THC,

then injected with a second chemical to block cannabis receptors in the brain.

Without the block, the sharp withdrawal symptoms can’t be seen because cannabis

clears so slowly that even heavily doped rats are likely to experience a gentle

wind down. Another debate rages over animal studies into the short-term effects

of marijuana on brain chemistry. Heroin, cocaine, alcohol and nicotine all

trigger a surge in the chemical dopamine in a small midbrain structure called

the nucleus accumbens. Many researchers regard this as a hallmark of an

addictive substance. Last year, experiments showed that cannabis presses the

same dopamine button in rats, leading to claims that the drug must be more

addictive than previously thought. To critics, it is just another example of

those old exaggerated fears. What nobody tells you, says John Morgan, a

pharmacologist at City University of New York Medical School, is that rats don’t

like cannabis. It’s easy for them to get hooked on heroin or cocaine — but not

marijuana. Nor, Morgan claims, are researchers exactly open about awkward

observations, such as the fact that there are plenty of nonaddictive drugs that

stimulate dopamine in the brain. It’s easy to understand why biologists want to

find simple chemical traits that are shared by all addictive drugs.

Unfortunately, the differences are as important as the similarities when it

comes to weighing the relative risks and pleasures involved in taking drugs. And

subjectively at least, the intense rush of cocaine and orgasm-like high of

heroin have little in common with dope’s subtler effects. A compound related to

the active ingredient in marijuana may be accumulating in the spinal fluid of

people with schizophrenia. This might explain why many sufferers smoke pot. Many

researchers blame schizophrenia on an overactive dopamine system in the brain.

Daniele Piomelli and colleagues at the University of California at Irvine

already knew that making rats? dopamine receptors hyperactive caused a surge in

anandamide, a lipid that binds to the same receptors in the brain as marijuana.

Now Piomelli?s group has examined cerebrospinal fluid from 10 schizophrenic

patients, taken for diagnostic purposes at the Medical College of Hannover in

Germany. They found that fluid from schizophrenic patients had on average twice

as much anandamide as fluid from people who didn?t have schizophrenia (NeuroReport,

vol 10, p 1665). One explanation for the higher levels in schizophrenics is that

the brain is attempting to compensate for a hyperactive dopamine system. ?It?s

the brain?s response to bring this dopamine activity down,? says Piomelli. But

the brain cannot keep the amount of anandamide high enough to lower dopamine

levels, he says. This might also explain why schizophrenics often smoke

marijuana. The drug?s active agent, THC, and anandamide both bind to the same

receptor, so patients might be treating themselves, he says. But because pot

does not act selectively in the brain, Piomelli does not consider it a useful

treatment for schizophrenia. ?I don?t think the patient wants to be high,? he

says. ?I think the patient wants to feel better.? One weakness in the data so

far is that five of the patients were taking medication for their symptoms and

three others were using marijuana daily. The effects of these drugs on

endogenous cannabinoid levels is not known. ?It is imperative to continue with

a larger sample,? says Piomelli. The researchers are now testing fluid from

more patients to see if the correlation still holds true. Health officials in

Geneva have suppressed the publication of a politically sensitive analysis that

confirms what ageing hippies have known for decades: cannabis is safer than

alcohol or tobacco. According to a document leaked to New Scientist, the

analysis concludes not only that the amount of dope smoked worldwide does less

harm to public health than drink and cigarettes, but that the same is likely to

hold true even if people consumed dope on the same scale as these legal

substances. The comparison was due to appear in a report on the harmful effects

of cannabis published last December by the WHO. But it was ditched at the last

minute following a long and intense dispute between WHO officials, the cannabis

experts who drafted the report and a group of external advisers. As the WHO’s

first report on cannabis for 15 years, the document had been eagerly awaited by

doctors and specialists in drug abuse. The official explanation for excluding

the comparison of dope with legal substances is that "the reliability and

public health significance of such comparisons are doubtful". However,

insiders say the comparison was scientifically sound and that the WHO caved in

to political pressure. It is understood that advisers from the US National

Institute on Drug Abuse and the UN International Drug Control Programme warned

the WHO that it would play into the hands of groups campaigning to legalise

marijuana. One member of the expert panel which drafted the report, says:

"In the eyes of some, any such comparison is tantamount to an argument for

marijuana legalisation." Another member, Billy Martin of the Medical

College of Virginia in Richmond, says that some WHO officials "went

nuts" when they saw the draft report. The leaked version of the excluded

section states that the reason for making the comparisons was "not to

promote one drug over another but rather to minimise the double standards that

have operated in appraising the health effects of cannabis". Nevertheless,

in most of the comparisons it makes between cannabis and alcohol, the illegal

drug comes out better–or at least on a par–with the legal one. The report

concludes, for example, that "in developed societies cannabis appears to

play little role in injuries caused by violence, as does alcohol". It also

says that while the evidence for fetal alcohol syndrome is "good", the

evidence that cannabis can harm fetal development is "far from

conclusive". Cannabis also fared better in five out of seven comparisons of

long-term damage to health. For example, the report says that while heavy

consumption of either drug can lead to dependence, only alcohol produces a

"well defined withdrawal syndrome". And while heavy drinking leads to

cirrhosis, severe brain injury and a much increased risk of accidents and

suicide, the report concludes that there is only "suggestive evidence that

chronic cannabis use may produce subtle defects in cognitive functioning".

Two comparisons were more equivocal. The report says that both heavy drinking

and marijuana smoking can produce symptoms of psychosis in susceptible people.

And, it says, there is evidence that chronic cannabis smoking "may be a

contributory cause of cancers of the aerodigestive tract". HEAVYusers of

marijuana who suddenly go cold turkey have aggressive impulses as powerful as

those felt by Frank Spooner The reaction is far less intense than the withdrawal

symptoms of alcoholics or people addicted to cocaine or heroin, and may reflect

a psychological dependence on the drug, rather than a genuine physiological

addiction. But it still might be enough to keep some marijuana users from

kicking their habit, says Elena Kouri, a psychologist at Harvard Medical School

in Boston. Kouri and her colleagues recruited 17 volunteers who had smoked

marijuana on at least 5000 occasions, and who continued to be heavy users of the

drug. They also studied 20 people who either took marijuana occasionally, or who

had already given it up. None of the volunteers had a history of violence or any

other psychiatric disturbance. The researchers used a computer game to measure

the volunteers’ aggressive behaviour during a 28-day period of abstinence from

marijuana, which was monitored by daily, supervised urine tests. The volunteers

sat alone at a computer screen with two buttons. The first added money to an

account in their name, but they were told that a second would subtract money

from the account of their opponent, sitting at a similar screen in the next

room. On the day they gave up marijuana, and one, three, seven and 28 days

later, the two players were given 20 minutes to take it in turns to push one or

other button, after which they could keep the money left in their account. In

reality, there was no opponent. The researchers had instead arranged for the

computer to provoke the volunteers by frequently subtracting money from their

account. When tested on the third and seventh days of abstinence, this ersatz

"nasty opponent" managed to get the heavy users noticeably hot under

the collar. Says Kouri: "Subjects that on day zero hadn’t cared at all that

they were losing points started swearing and punching the keyboard, yelling ‘I’m

going to get you back!’" The heavy users hit the "punishment

button" more than twice as often as the control group on days three and

seven– an increase in aggression that compares roughly with that produced by a

three-week course of testosterone supplements in another study by Kouri. The

increased aggression had subsided completely by the time the volunteers were

tested again at the end of the abstinence period, however (Psychopharmacology,

vol 143, p 302). The study is the first to measure aggression during withdrawal

from a long period of heavy marijuana use. But Margaret Haney, a psychologist at

Columbia University in New York, says that people who show aggressive tendencies

in the laboratory do not necessarily become violent in the real world. "I

would hesitate to say that it would translate to physical violence," she


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