Pubdate: Tue, 08 Jan 2013
Source: New York Times (NY)
Copyright: 2013 The New York Times Company
Author: Roni Caryn Rabin


In the '60s, marijuana was a hallmark of the counterculture, along 
with free love, bell bottoms, long hair and bandannas. But marijuana 
has had the most staying power.

This month, in a remarkable first, the recreational use of marijuana 
became legal (depending on your definition) in Colorado and 
Washington. Over a dozen other states have decriminalized possession 
of small amounts, and Massachusetts recently became the 18th state to 
allow its use for medicinal purposes.

Though federal law still bans both the sale and possession of 
marijuana, President Obama has said the federal government has 
"bigger fish to fry" and won't aggressively prosecute tokers in 
states where its use is legal.

The rise of marijuana as an adult pastime is a victory for those 
who've always felt that its hazards were overblown. Proponents of 
legalization argue that marijuana is much safer to use than alcohol, 
pointing out that it is virtually impossible to overdose on marijuana.

While marijuana can be addictive, scientists generally agree that 
fewer than 10 percent of marijuana smokers become dependent on the 
drug, compared with 15 percent for alcohol, 23 percent for heroin and 
32 percent for tobacco. Marijuana does contain carcinogens, including 
tar and other toxins similar to those found in tobacco, but people 
generally do not smoke marijuana in the same amounts as cigarettes.

Still, legalization takes health consumers into murky territory. Even 
though marijuana is the most commonly used illegal drug in the United 
States, questions about its health effects remain.

For starters, this is not your parents' pot. Today's marijuana is 
much more potent: The mean concentration of THC, the psychoactive 
ingredient, in confiscated cannabis more than doubled between 1993 and 2008.

Increased potency may be having unforeseen consequences. The human 
brain's cannabinoid receptors are typically activated by naturally 
occurring chemicals in the body called endocannabinoids, which are 
similar to THC. There is a high density of cannabinoid receptors in 
parts of the brain that affect pleasure, memory and concentration. 
Some research suggests that these areas continue to be affected by 
marijuana use even after the "high" dissipates.

"It's much more potent marijuana, which may explain why we've seen a 
pretty dramatic increase in admission to emergency rooms and 
treatment programs for marijuana," said Dr. Nora D. Volkow, director 
of the National Institute on Drug Abuse. "When we hear, 'Well, I 
smoked and nothing happened to me,' we need to think about the 
context of when these people started to take it, how frequently they 
used and how active the marijuana was."

Those in favor of legalizing marijuana say the increase in potency 
has been exaggerated, and that when users have more powerful pot, 
they adjust their consumption and actually smoke less.

Teenagers may be more vulnerable to addiction, however, and those who 
start smoking pot at a younger age are at higher risk. Approximately 
one in six will become addicted, Dr. Volkow said. Young adults who 
start smoking marijuana at earlier ages also tend to smoke much more, 
and more often, than those who start in their later teens, researchers say.

In users who develop a dependence or addiction, quitting can cause 
intense withdrawal symptoms, like anxiety, trouble sleeping, lack of 
appetite, mood swings, irritability and depression, experts say.

Both Colorado and Washington restricted marijuana use to adults age 
21 and over when they legalized recreational use in November. But 
experts worry that the perception of marijuana is changing because 
its stigma as an outlawed drug has eroded.

"When people can go to a 'clinic' or 'cafe' and buy pot, that creates 
the perception that it's safe," said Dr. A. Eden Evins, director of 
the Center for Addiction Medicine at Massachusetts General Hospital 
in Boston. "Before we unleash the powers of the marketplace to woo 
people to use this addictive substance, we need to better understand 
who is at risk."

"Once moneyed interests are involved, this trend will be difficult to 
reverse," she added.

The most disturbing new studies about early teenage use of marijuana 
showed that young adults who started smoking pot regularly before 
they were 16 performed significantly worse on cognitive tests of 
brain function than those who had started smoking later in 
adolescence. They performed particularly poorly on tests assessing 
executive function, which is responsible for planning and abstract 
thinking, as well as understanding rules and inhibiting inappropriate 

Imaging scans also found detectable differences in how their brains 
worked, said Staci Gruber, the lead author of these studies and 
director of the cognitive and clinical neuroimaging core at the 
imaging center at McLean Hospital in Boston. Imaging scans found 
alterations in the frontal cortex white matter tracts of the brain in 
the early-starters, she said, that are associated with impulsiveness.

"The frontal cortex is the last part of the brain to come online, and 
the most important," Dr. Gruber said. "Early exposure perhaps changes 
the trajectory of brain development, such that ability to perform 
complex executive function tasks is compromised."

A recent study showing a drop in IQ scores among teenagers who are 
regular pot smokers is especially troubling, Dr. Evins said. A more 
recent study found that people who started smoking marijuana as 
teenagers and used it heavily for decades lost IQ points over time, 
while those who started smoking as adults did not, though some 
critics have said these differences may not be meaningful. Older 
survey studies had indicated that regular pot smokers were less 
likely to graduate from high school or pursue higher education, but 
it was never clear which came first, difficulty in school or the drug use.

"If parents who are spending thousands of dollars on SAT prep courses 
knew about the cognitive effects marijuana has on their kids' brains, 
they would be up in arms," Dr. Evins said. Other health concerns 
about marijuana are less well documented but may turn out to be 
significant. States that legalized marijuana prohibit driving under 
its influence, and studies have found marijuana smoking increases 
weaving between lanes and slows reaction times. And although 
marijuana is not as damaging to the lungs as tobacco, in part because 
people do not smoke a pack of joints a day, a regular habit can 
eventually take a toll on the lungs.

At the very least, the new studies suggest parents who recall their 
own pot parties may want to suggest greater moderation to their 
children. And teenagers who insist on trying marijuana are better off 
waiting until they're older.

"It's the same message as with alcohol," Dr. Gruber said. "Just hold 
on, it's worth it to wait."
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