The development of a drug abuse problem is caused by a combination of biological and environmental factors. In each case, the contributors are unique in causing the problem, and no single factor can be isolated as the trigger for drug abuse.
A study provides evidence that demonstrates the strong influence that environmental factors have on the development of a drug abuse problem. The researchers refer to it as a “potent influence” within families.
The study—led by Kenneth S. Kendler, MD, of the Virginia Institute for Psychiatric and Behavioral Genetics in Richmond—is a nationwide study of Swedish families. The researchers found that even after controlling for genetic variables, the risk for abusing drugs was higher for individuals who had a spouse or a sibling who also abused drugs.
The findings add support to research conducted by the same team that demonstrated the strength of environmental factors within families on the development of drug abuse among adopted children in Sweden.
The study is published in the online version of the journal Archives of General Psychiatry. Its analysis included in the study was based on the findings among 137,199 sibling pairs and 7,561 spouse pairs derived from nine databases dating from 1961-2009.
The researchers used conditional logistic regression analysis to determine that the siblings of case subjects were at a significantly higher risk for developing a drug abuse problem when compared with controls. This association was substantially higher for same-sex sibling pairs.
The study also showed that the influence of sibling drug abuse strengthened by age difference, with siblings closer in age having a stronger influence over drug use. A sibling born in the same year as an addict was twice as likely to develop a drug abuse problem as a sibling born ten years apart.
The researchers explain in the findings that the results served to isolate environmental effects because only full siblings were considered in their analysis, ensuring that each pair shared the same level of genetic influence.
Overall, the study showed that there was a 42% increased risk for drug abuse if an older sibling had a history of drug abuse.
In their findings, the researchers also presented their analysis for the influence a drug-abusing spouse has on their partner. Once a spouse was registered in a drug abuse database, his or her partner’s risk of also being registered in a database in the same year increased by 25 times. After several years, this risk decreased to six times the increased likelihood of being entered in a drug abuse database.
The researchers note that the findings provide important information about the influence of environmental factors on drug abuse. The study’s findings provide a foundation for understanding how biological and environmental factors work together to contribute to the development of a substance use disorder.