Pubdate: Fri, 07 Aug 1998 Source: Fox News Online Contact: comments@foxnews.com Author: Reuters

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.