'MARIJUANA AS ADDICTING AS COCAINE AND HEROIN'

NIDA Researchers Find That Animals Exposed to Marijuana's Active Component
Will Self-Administer the Drug

Scientists at the National Institute on Drug Abuse (NIDA) have demonstrated
that laboratory animals will self-administer marijuana's psychoactive
component, THC (delta-9-tetrahydrocannabinol), in doses equivalent to those
used by humans who smoke the drug. Self-administration of drugs by animals,
long considered a model of human drug-seeking behavior, is characteristic
of virtually all addictive and abused drugs.

"This study is simple and its findings are clear," says NIDA Director Dr.
Alan I. Leshner. "Animals will work to get THC. This emphasizes further the
similarity between marijuana and other abusable, addicting substances. Both
animals and humans will work to acquire access to marijuana in the same way
that both animals and humans change their behavior to get other drugs of
abuse, like cocaine and heroin."

Dr. Steven Goldberg and colleagues at NIDA's Intramural Research Program in
Baltimore, Maryland, report in the current issue of Nature Neuroscience
that squirrel monkeys will self-administer intravenous injections of THC.

"This is the first study in which it has been possible to show that monkeys
or other research animals will self-administer THC. There are many factors
which may explain this behavior, including the fact that in our study we
used doses of THC that are directly comparable to doses in marijuana smoke
inhaled by humans," Dr. Goldberg says.

Before the study began, the scientists first established
self-administration behavior in squirrel monkeys that received repeated
intravenous injections of cocaine after pressing a lever 10 times for each
injection. At the start of the study, the researchers replaced cocaine with
saline solution and the animals' self-administration stopped. When saline
was replaced with THC in a solution that would rapidly pass from blood to
the brain, the animals resumed self-administration, rapidly pressing the
lever to obtain on average 30 injections of THC during each of a series of
1-hour sessions. Treatment with a compound that prevented THC from binding
to cannabinoid receptors on brain cells almost completely eliminated
self-administration of THC, but had no effect in another group of monkeys
self-administering cocaine under identical conditions, according to Dr.
Goldberg.

"The drug-seeking behavior in these animals was comparable in intensity to
that maintained by cocaine under identical conditions, and was obtained
from a range of doses comparable to those self-administered by humans
smoking a single marijuana cigarette," Dr. Goldberg says. "This finding
suggests that marijuana has as much potential for abuse as other drugs of
abuse, such as cocaine and heroin."

Note to reporters: The full text of the brief communication about this
study is available in Nature Neuroscience 2000, volume 3, pgs 1073-74 or at
http://www.neurosci.nature.com/

The National Institute on Drug Abuse is a component of the National
Institutes of Health, U.S. Department of Health and Human Services. NIDA
supports more than 85 percent of the world's research on the health aspects
of drug abuse and addiction.