MARIJUANA SPECIAL REPORT: CLAIM FOUR:

"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.