WEDNESDAY, March 7, 2012 (HealthDay News) -- Adopted kids are at greater risk for drug abuse if their biological parents or siblings had a history of drug abuse, a new study finds.
Adopted children whose biological parents were alcoholics, had a major psychiatric illness or had criminal records were also at greater risk of drug abuse, the researchers reported.
However, biology and genetics don't tell the whole story, according to study author Dr. Kenneth Kendler, of Virginia Commonwealth University, and his colleagues.
The children's environment also played a role in their risk for drug abuse, Kendler's team found. Adopted children who had difficulties in their adoptive families because of death, divorce or other problems were at increased risk of turning to drugs, while the genetic risk wasn't as strong among adopted kids in safe, stable, loving homes.
"Adopted children at high genetic risk were more sensitive to the pathogenic effects of adverse family environments than those at low genetic risk," the researchers concluded. "In other words, genetic effects on [drug abuse] were less potent in low-risk than high-risk environments."
For the study, published online March 5 in the Archives of General Psychiatry, researchers examined information on more than 18,000 Swedish people with an average age of 46 who had been adopted.
The investigators also analyzed information on the participants' biological parents and siblings, and their adoptive parents to assess what role genetics and environmental factors played in their risk for drug abuse.
About 4.5 percent of people who were adopted abused drugs compared with 2.9 percent for all people born in Sweden during the same time period, the study authors noted in a journal news release.
The risk for drug abuse among adopted children with at least one biological parent that abused drugs was 8.6 percent compared to 4.2 percent among adopted kids whose biological parents did not abuse drugs. The researchers noted this was a "substantially and significantly" increased risk.
The U.S. National Institute on Drug Abuse has more about the genetics of addiction.