Addled? Could Be the Marijuana
Heavy Use Might Prime the Brain for Other Addictions
By Sandra Blakeslee
New York Times Service

NEW YORK People who regularly smoke large amounts of
marijuana may experience changes in their brain chemistry that are
identical to changes seen in the brains of people who abuse heroin,
cocaine, amphetamines, nicotine and alcohol scientists have found.
The findings, based on studies of rats, were published Friday in
the journal Science. They provide strong support for the emerging idea
that all addictive drugs corrupt the same brain circuits, although to
varying degrees, and suggest that chronic marijuana use may literally
prime the brain for other drugs of abuse, a notion known as "the
gateway effect."
While the studies were conducted on rats, researchers are
confident that the find ings will apply to humans virtually all of the
biological mechanisms known to cause drug addiction were discovered
in animal models before being established in humans.
People who oppose the legalization of marijuana will be happy
about these findings, while those who feel that marijuana is a benign
drug will probably be upset, said Dr. Alan Leshner, director of the
National Institute on Drug Abuse in Rockville Maryland, which financed
the research.
According to this new hypothesis, addictive drugs like nicotine
heroin and cocaine all work through common pathways in the brain.
One pathway is responsible for feelings of reward, and a second
pathway underlies feelings of anxiety brought on by stress. In street
drug parlance, one system produces the "high" while the other
produces withdrawal.
But many people thought marijuana was different because
overt feelings of withdrawal are uncommon, said Dr. George Koob, a
pharmacologist at the Scripps Research Institute in San Diego.
The reason is that marijuana's active ingredient THC has a long
halflifemeaning it lingers in the bloodstreamwhich in turn prevents
the abrupt withdrawal symptoms seen in fastacting drugs like nicotine,
he said.