Though some studies point to negative
consequences of pot use in adolescents, data on marijuana’s dangers are
mixed.
Flickr, PabloEvans
Marijuana is a tricky drug, alternately
demonized as a gateway drug and lionized for its medical
promise. And while the juries remain out on both sides of the coin, one
thing is clear: its use is on the rise. According to the US Department of Human
Health and Services, the number of people in the United States who admit to
smoking pot in the last month climbed from 14.4 million in 2007 to over 18
million in 2011.
This increase may in part be due to the lack of strong evidence supporting
the suspected risks of cannabis use. Indeed, though marijuana smoke carries
carcinogens and tar just as tobacco smoke does, definitive data linking
marijuana to lung damage is lacking. And a recent long-term study that seemed to
conclusively link chronic
marijuana initiated in adolescence to a lowered IQ in New Zealanders was
quickly challenged by a counter-analysis that
pointed to socioeconomic status as a confounding factor. According to survey
data from the Centers for Disease Control and Prevention, cannabis use increases
in teenagers as marijuana’s perceived risks decline, and researchers—and
undoubtedly some parents—are anxious to get to the bottom of the matter.
Take a deep breath
In 2012, a study at
the University of California, San Francisco (UCSF) calculated that even smoking
a single joint every day for 20 years might be benign, though most participants
only smoked two or three joints each month. “I was surprised we didn’t see
effects [of marijuana use],” said UCSF epidemiologist Mark
Pletcher, who led the study.
One assessment of
various epidemiological studies points to small sample size and poor study
design as reasons for scientists’ inability to nail down a link between cannabis
and cancer risk. But some suspect that such a link doesn’t exist, and that
marijuana may even have cancer-preventive effects. A 2008 study, for example,
suggested that smoking marijuana may reduce the risk of tobacco-associated lung
cancer, calculating that people who smoke both marijuana and tobacco have a
lower risk of cancer than those who smoke only tobacco (though still a higher
risk than non-smokers).
But even Pletcher isn’t sanguine about marijuana’s effects on the lungs, and
suspects that there may still be long-term lung damage that can be hard to
detect. “We really can’t reassure ourselves about heavy use,” he explained.
Your brain on drugs
There is some evidence to suggest that stoned subjects exhibit increased
risk-taking and impaired decision-making, and score worse on memory tasks—and
residual impairments have been detected days or even weeks after use. Some
studies also link years of regular marijuana use to deficits in memory,
learning, and concentration. A recent and widely discussed report on the IQs of New
Zealanders followed since birth found that cannabis users who’d started their
habit in adolescence had lower IQs than non-users.
In this study, led by researchers at Duke University, “you could clearly see
as a consequence of cannabis use, IQ goes down,” said Derik Hermann, a clinical
neuroscientist at the Central Institute of Mental Health in Germany who was not
involved in the research.
But not 4 months later, a re-analysis and computer
simulation at the Ragnar Frisch Center for Economic Research in Oslo
countered the Duke findings. Ole Rogeberg contended that socioeconomic factors,
not marijuana use, contributed to the lower IQs seen in cannabis users.
Rogeberg’s conclusion counters a sizeable literature, however, which supports
a link between pot use and neurophysiological decline. Studies in both humans
and animals suggest that people who acquiring a marijuana habit in adolescence
face long-term negative impacts on brain function, with some users finding it
difficult to concentrate and learn new tasks.
Notably, most studies on the subject suggest that while there may be negative
consequences of smoking as a teen, users who begin in adulthood are generally
unaffected. This may be due to endocannabinoid-directed reorganization of the
brain during puberty, Hermann explained. The intake of cannabinoids that comes
with pot use may cause irreversible “misleading of the neural growth,” he
said.
In addition to the consequences for intelligence, many studies suggest that
smoking marijuana raises the risk of schizophrenia, and may have similar effects
on the brain. Hermann’s group used MRI to detect cannabis-associated neuron
damage in the pre-frontal cortex and found that it was similar to brain
changes seen in schizophrenia patients. Other studies further suggest that
weed-smoking schizophrenics have greater disease-associated
brain changes and perform
worse on cognitive tests than their non-smoking counterparts.
But much of this research can’t distinguish between brain changes resulting
from marijuana use and symptoms associated with the disease. It’s possible that
cannabis-smoking schizophrenics “might have unpleasant symptoms [that precede
full-blown schizophrenia] and are self-medicating” with the psychotropic drug,
said Roland
Lamarine, a professor of community health at California State University,
Chico. “We haven’t seen an increase in schizophrenics, even with a lot more
marijuana use.”
In fact, other research suggests that cannabis-using
schizophrenics score better on cognitive tests than non-using
schizophrenics. Such conflicting reports may be due to the varying
concentrations—and varying effects—of cannabinoids in marijuana. In addition to
tetrahydrocannabinol (THC), a neurotoxic cannabinoid that is responsible for
marijuana’s mind-altering properties, the drug also contains a variety of
non-psychoactive cannabinoids, including cannabidiol (CBD), which can protect
against neuron damage. Hermann found that the volume of the hippocampus—a brain
area important for memory processing—is slightly smaller in cannabis users than
in non-users, but more CBD-rich marijuana countered this
effect.
A deadly cocktail?
While data supporting the harmful effects of marijuana on its own are weak,
some researchers are more worried about the drug in conjunction with other
substances, such as tobacco, alcohol, or cocaine. Some studies suggest, for
example, that marijuana may increase cravings for other
drugs, leading to its infamous tag as a “gateway drug.” A study published
earlier this month supported this theory when it found that, at least in rats,
THC exposure increases
tobacco’s addictive effects. Furthermore, marijuana may not mix well with
prescription drugs, as cannabis causes the liver to metabolize drugs more
slowly, raising the risk of drug toxicity.
Despite these concerns, however, Lamarine thinks it’s unlikely that the
consequences of cannabis use are dire, given the amount of research that has
focused on the subject. “We’re not going to wake up tomorrow to the big
discovery that marijuana causes major brain damage,” he said. “We would have
seen that by now.”
Source: TheScientist
http://www.the-scientist.com//?articles.view/articleNo/34110/title/Is-Cannabis-Really-That-Bad-/
http://www.the-scientist.com//?articles.view/articleNo/34110/title/Is-Cannabis-Really-That-Bad-/
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Robert Karl Stonjek
Robert Karl Stonjek
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