GENES MAY INFLUENCE MARIJUANA USE

NEW YORK, - A study of female twins suggests that in women, genes may play a
role in heavy marijuana use.

"Genetic risk factors have a moderate impact on the probability of ever
using cannabis and a strong impact on the liability to heavy use, abuse,
and, probably, dependence,'' conclude researchers Dr. Kenneth Kendler of
Virginia Commonwealth University and Dr. Carol Prescott of the Virginia
Institute for Psychiatric and Behavioral Genetics, both located in Richmond,
Virginia.

Their study, published in the August issue of the American Journal of
Psychiatry, evaluated interviews conducted with over 1,900 female twins
(both identical and fraternal).

The authors report that nearly half of the women (47.9%) said they had used
marijuana at some point in their lives. About 7% reported going through a
period of either heavy use (more than 10 uses per month) or actual cannabis
abuse. The authors say 2.2% of the women reported being marijuana dependent.

A detailed comparison of cannabis use among twins revealed that nongenetic
factors like family environment do "play an important...role'' in the
likelihood that a woman would at least experiment with marijuana at some
point in her life, according to the investigators.

However, "given initiation (into marijuana use),'' they say ''the risk for
progression to heavy use, abuse and dependence appears to be largely
independent of the family environment and heavily determined by (genetics).
"In fact, the authors speculate "that genetic factors are responsible for
60% - 80% of the variance in liability'' towards marijuana dependence among
women.

The behavior patterns of identical twins suggest that genetic makeup
increases the risk for marijuana use through a phenomenon the authors call
"genetic control of exposure to the environment.'' This theory holds that
individuals with certain genes are drawn to certain types of stimuli (such
as social gatherings) that might encourage drug use.

Genes might also influence the likelihood of marijuana use through their
ability to render 'pot' intoxication more or less pleasurable. Kendler and
Prescott say the genes of some users may simply encourage a greater 'high'
from cannabis use, raising the likelihood for continued use or abuse.

But the authors also caution that the number of cannabis abusing twins
included in their study was small, and that twin studies cannot match the
accuracy of laboratory studies. "We cannot rule out the possibility that our
results are influenced by hidden biases,'' they say.

SOURCE: American Journal of Psychiatry 1998;155:1016-1022.

1998, News America Digital Publishing, Inc. All rights reserved.
Reuters Ltd. All rights reserved

Checked-by: Melodi Cornett