Illicit drug use and abuse may be genetic…Findings replicated in twin study based in Norway – a country with lower prevalence of drug use than the United States and Australia

RICHMOND, Va. (July 5, 2006) – Researchers have found that genetic factors may play an important role in a person’s use, misuse or dependence of illicit drugs like marijuana, stimulants, opiates, cocaine and psychedelics.

In the July issue of the journal Psychological Medicine, Virginia Commonwealth University researchers, in collaboration with researchers from Norwegian Institute of Public Health and University of Oslo in Norway, reported the results of a population-based study of twin pairs that showed that genetic factors influence the illicit drug use in Norway, a country with significantly low levels of psychoactive substance use disorder.

“Prior twin studies of illicit drug use and abuse have all been conducted in Anglophonic countries, specifically the United States and Australia, with high levels of such use. This is the first study of a non-English speaking country with much lower rates of drug use - yet results are similar - drug use and abuse or dependence is quite heritable,” said lead author Kenneth S. Kendler, M.D., a professor of psychiatry and human genetics in VCU’s School of Medicine.

The team examined the role of genetic and environmental factors in the progression of psychoactive substance use and abuse.

Approximately 1,400 young adult twin pairs from the Norwegian Institute of Public Health Twin Panel were interviewed and assessed for their lifetime use of illicit drugs, including marijuana, stimulants, opiates, cocaine and psychedelics. Researchers defined the significant lifetime use of illicit substances as use 10 or more times.  

Previous theories have suggested that genetic factors might be of less importance in influencing drug use in societies where drugs were not widely available. According to Kendler, the results of this study are inconsistent with this theory.  

“In addition to prior findings, the results of this investigation indicate that genetic factors are likely to be important risk factors for psychoactive drug use and misuse in many parts of the world,” he said. 

This work was supported in part by grants from the National Institutes of Health, the Norwegian Research Council, the Norwegian Foundation for Health and Rehabilitation, The Norwegian Council for Mental Health and the European Commission.  

Kendler collaborated with Steven H. Aggen, Ph.D., in the department of psychiatry at VCU; and Kristian Tambs, Ph.D., and Ted Reichborn-Kjennerud, M.D., who are affiliated with the Division of Mental Health and Institute of Psychiatry, Norwegian Institute of Public Health; and University of Oslo Norway.