"These findings bring home the reality that abuse of any illicit drug threatens an individual's well-being and may have serious, unexpected ramifications," said NIDA Director Dr. Alan I. Leshner. "In the critical search for improved treatments for drug addiction, this study documents the importance of continuing research on the different social, psychological, genetic, and environmental factors that can influence a person's vulnerability to drug abuse."
Previous research has shown that genetic and environmental factors can influence the risk of drug abuse, but evidence from this study indicates that such factors not only influence the risk of drug abuse but also increase one's vulnerability to abusing every other illicit drug. Furthermore, researchers found that genetic and environmental factors do not have the same level of influence with each drug. For example, while family environment influenced use of all illicit drugs to some extent, marijuana use appeared to be so influenced to a greater extent than did other drug use. Also, while vulnerability to abuse of most drugs includes genetic influences that relate specifically to a particular drug, heroin had more unique genetic influences than any other drug studied.
"We investigated the extent to which the abuse of different categories of drugs occurs together within an individual," said the study's principal investigator, Dr. Ming T. Tsuang, of Harvard University. "At the same time, we examined the possibility that genetic and environmental factors, including family environment, are responsible for such co-occurrences," he said.
Researchers interviewed 3,372 pairs of male twins (6,744 men), ages 36 to 55. Both twins had served in the Vietnam War and, based on the America Psychiatric Association's objective DSM-III-R diagnostic criteria, both reported abusing an illicit drug at some point in their lives. Analyzing the extent of co-occurring drug abuse among twins helped researchers to estimate the potential influence of genetic and environmental factors on drug abuse.
Because the pattern and prevalence of drug abuse in the study sample of Vietnam era veterans is similar to drug abuse in the general male population, the investigators believe that the study's results may apply to men of approximately the same age group who are nonveterans. However, because no women participated in the study, it is not known whether these results are applicable to women.
NIDA supports more than 85 percent of the world's research on the health aspects of drug abuse and addiction. The Institute carries out a large variety of programs to ensure the rapid dissemination of research information and its implementation in policy and practice.
Further information on NIDA research and other activities can be found on the NIDA home page at http://www.nida.nih.gov. Fact sheets on health effects of drugs of abuse and other topics can be ordered free of charge, in English and Spanish, from NIDA Infofax at 1-888-NIH-NIDA (-644-6432) or 1-888-TTY-NIDA (-889-6432) for the deaf.