Health The Science of Health
May 31, 2013
As more states make recreational marijuana legal, researchers fret about short- and long-term health effects
Marijuana is more popular and accessible in the U.S. than any other
street drug. In national surveys, 48 percent of Americans say they have
tried it, and 6.5 percent of high school seniors admit to daily use. So
it was not too surprising when two states, Washington and Colorado,
became the first to legalize recreational marijuana in the November 2012
general election, albeit in limited quantity, for anyone over the age
of 21. Activists expect that similar measures will soon win approval in
other parts of the country.
Some success with medical marijuana helped to pave the road to wider
legalization of pot. Eighteen states and the District of Columbia permit
possession and consumption of the drug for medical purposes. Doctors in
those jurisdictions may prescribe cannabis to treat or manage ailments
ranging from glaucoma—an eye disease in which the optic nerve is
damaged—to menstrual cramps.
Cancer patients sometimes smoke pot to relieve the
pain
and nausea brought on by chemotherapy, and some people with the
inflammatory disease multiple sclerosis rely on marijuana to ease muscle
stiffness.
Although many physicians agree that marijuana is safe enough to
temporarily alleviate the symptoms of certain medical conditions, the
safety of recreational use is poorly understood. Researchers worry that
both the short- and long-term use of the drug may harm the body and
mind. Marijuana's continued popularity among teenagers raises particular
concern because the drug might hinder the ongoing maturation of the
adolescent brain. Making matters worse, new growing techniques for the
Cannabis sativa
plant—from which marijuana is prepared—have dramatically increased the
drug's potency. Some experts suggest that such high-octane weed is
fueling a rise in cannabis addiction. Finally, although investigators
still debate how the legalization of recreational marijuana will change
road safety overall, studies indicate that the drug slows reaction time
and impairs distance perception behind the wheel. Despite such evidence,
most new marijuana regulations, for medical or recreational use, fail
to account for these potential risks.
Weeded Out
Whether rolled into a joint or mixed into brownie batter, marijuana
profoundly changes behavior and awareness. The primary psychoactive
compound in marijuana, tetrahydrocannabinol (THC), mimics the structure
of molecules called endocannabinoids that the human body produces
naturally. Endocannabinoids act on a group of cell-surface molecules
called cannabinoid receptors that help to regulate appetite, mood and
memory. Because of its shape, THC fits into these receptors, too. After
all, jokes neuroscientist Giovanni Marsicano of the University of
Bordeaux in France, “We don't have a receptor in the body just to smoke
marijuana.”
When THC strikes specific cannabinoid receptors, it triggers domino
chains of interacting molecules in neurons that culminate in both
unusually elevated and abnormally low levels of various
neurotransmitters (the molecules that brain cells use to communicate
with one another). The result is the well-known “high” of marijuana.
Suddenly, the mundane seems hilarious, and ordinary foods taste
delicious. People generally feel merry, relaxed and introspective,
although undesirable effects—such as paranoia and irritability—are
common as well.
Marijuana also temporarily impairs an array of mental abilities,
especially memory and attention. Dozens of studies have shown, for
example, that people under the influence of marijuana perform worse on
tests of working memory, which is the ability to temporarily hold and
manipulate information in one's mind. Participants in these studies have
greater difficulty remembering and reciting short lists of numerals and
random words. Research has further revealed that cannabis blunts
concentration, weakens motor coordination and interferes with the
ability to quickly scan one's surroundings for obstacles.
Such mild cognitive deficits may not endanger anyone if a marijuana user
lazes on the couch, but it is a different story when someone takes that
high on the road. In driving-simulation and closed-course studies,
people on marijuana are slower to hit the brakes and worse at safely
changing lanes. Investigators still debate, however, at what point these
impairments translate to more traffic accidents. A 2009 study found an
increased risk of accidents for levels of THC higher than five nanograms
per milliliter of blood, which some evidence indicates is as impairing
as a blood alcohol concentration around the legal limit of 0.08 percent.
Typically one would have to take several puffs of a joint to reach such
a concentration. Consequently, voters in Washington State have adopted 5
ng/mL as the upper threshold for drivers.
Enforcing that limit presents a technical challenge, however. Unlike
alcohol, marijuana cannot be detected with a relatively unobtrusive
Breathalyzer test. Police officers would have to look for it in
blood—something that often requires a warrant. “There is currently no
practical method for law-enforcement officers at the scene to collect
blood samples from suspected DUI cannabis drivers in a timely manner,”
says Paul Armentano, deputy director of the Washington, D.C.–based
National Organization for the Reform of Marijuana Laws, which advocates
the legalization of marijuana. Instead of using a blood test, Armentano
says that police should look for poor maneuvering and the smell of pot
wafting from the vehicle.
Smoke Signals
Although marijuana's immediate effects are relatively easy to monitor in
the lab, the drug's long-term effects on body and mind are harder to
determine. So far the results—which admittedly are subject to multiple
interpretations—indicate the need for caution. In one recent study,
clinical psychologist Madeline Meier of Duke University and her
colleagues examined data from 1,037 New Zealanders. They found that
people who began using pot earlier in life and used it most frequently
over the years experienced an average decline of eight IQ points by the
time they turned 38. By comparison, those who never smoked pot had an
average increase of one IQ point by the same age.
A reanalysis of the New Zealand data by Ole Røgeberg of the Ragnar
Frisch Center for Economic Research in Oslo, however, suggested that the
IQ difference could be explained by socioeconomic factors. People who
start
smoking
marijuana at an earlier age are often less intelligent to begin with.
Even if this is true, Meier says, her study shows that the IQ drop is
greatest for those who started smoking pot as teenagers rather than in
adulthood, indicating a worrisome cumulative effect regardless of
intelligence. This finding, she thinks, makes it all the more important
to discourage the early use of marijuana among teens.
Increasingly potent marijuana of recent years may be driving a sharp
rise in cannabis addiction among adolescents, according to a report
released last year by the American Society of Addiction Medicine.
Between 1993 and 2008, the average concentration of THC in confiscated
marijuana jumped from 3.4 to 8.8 percent. Meanwhile hospital and
rehabilitation center admission rates for minors abusing marijuana
soared by 188 percent between 1992 and 2006. In contrast, admissions for
alcohol abuse for the same group over the same period declined by 64
percent.
In addition to tracking levels of THC itself, some researchers have
focused on the dangers of lingering contaminants in marijuana sold on
the street. Dealers typically sell cannabis by weight, so some use sand
or glass beads to make their products heavier. Breathing in these
particles over the years may inflame and eventually scar the lungs. An
analysis published last year of data on more than 5,000 Americans did
not find a decline in lung function among individuals who smoked joints
two or three times a month over two decades. The authors emphasize,
however, that they did not assess the effect of daily use on lung
health. “Somebody should do that study if marijuana is going to become
legalized and prescribed” more widely, says Mark Pletcher, an
epidemiologist at the University of California, San Francisco, who
co-wrote the paper.
Some opponents of legalization worry that lax regulation of medical
marijuana foretells even looser laws concerning recreational marijuana.
In states that have legalized medical pot, current laws do not guarantee
the safety or quality of cannabis products or standardize levels of
THC. In Oakland, Calif., people can fill a marijuana prescription at
Harborside Health Center, a massive dispensary with a strict
quality-control system. Elsewhere in the state, however, people get
their medical marijuana at mom-and-pop outfits or on the street. The
next big round of ballot initiatives to legalize cannabis in states
other than Washington and Colorado could happen as soon as three years
from now, in the 2016 presidential election. Until then, researchers
have plenty of marijuana health risks to weed through.
This article was originally published with the title Going to Pot.
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