Illicit drug of choice is personal, VCU study finds

By Lorraine Cichowski and Kenneth Kendler

RICHMOND, Va. – Researchers have long documented that drug abuse runs in families, but genetics and the home environment appear to have little impact on a person’s illegal drug of choice, according to researchers at the Virginia Commonwealth University Medical Center.

The VCU researchers reviewed data from interviews with nearly 1,200 pairs of male adult twins about their history of use, abuse and/or dependence on marijuana, cocaine, hallucinogens, sedatives, stimulants and opiates. They concluded that genetic factors and family environment had an impact on a person’s predisposition to use and abuse a wide range of illicit substances.  But other environmental factors not shared by members of a twin pair, such as easy access to a specific drug, appeared to determine which specific illicit drug or drugs were used.

“One common genetic factor and the shared home environment were found to have a strong influence on the risk for illicit use, abuse and dependence for all six substances,” said behavioral geneticist Kenneth S. Kendler, M.D., professor of psychiatry and director of the Virginia Institute for Psychiatric and Behavioral Genetics at VCU. “But we could not find evidence for genetic or shared environmental factors that increased the risk for individuals to abuse substance A and not also to abuse substances B, C and D.

“Just because parents or friends smoke marijuana doesn’t mean that someone will necessarily choose marijuana and not other illicit psychoactive substances.”

Kendler noted that the twin study was not designed to pinpoint the genes on the human genome that would make someone susceptible to drug use.  He said this study, however, had implications for that research because it suggests that the search for genetic variations that affect human drug abuse should focus on factors that increase or decrease risk for the abuse of all types of illegal substances, not just a specific drug.

The twins included in the study, which was published in the April issue of the American Journal of Psychiatry, were born in Virginia between 1940 and 1974. They are part of VCU’s Mid-Atlantic Twin Registry, which contains information on more than 32,000 pre-school, school age and adult twins born or living in Virginia and North Carolina.