However, trouble or substance abuse in the adoptive family is also a risk factor, according to a study of more than 18,000 adopted children in Sweden.
This suggests that both environment and biological family history can influence a child's likelihood of future drug use.
"For someone at low genetic risk, being in a bad environment conveys only a modestly increased risk of drug abuse," says lead study author Dr. Kenneth S. Kendler, professor of psychiatry and human genetics at Virginia Commonwealth University in Richmond. "But if you are at high genetic risk, this can put your risk for drug abuse much higher."
The findings should be reassuring to adoptive parents, and to people who are thinking about adopting, because they show the importance of a positive environment, experts say.
"A child who is adopted, just like a child who is biological, does carry a certain genetic risk, but this shows that the environment they're being raised in and how their genetic risk interacts with that is probably much more important for the potential development of any disease, including substance abuse and dependence," says Dr. Lukshmi Puttanniah, director of child and adolescent psychiatry at Lenox Hill Hospital in New York, who was not involved with the study.
The study, published this week in the Archives of General Psychiatry, included 18,115 children born in Sweden between 1950 and 1993 and later adopted. Overall, 4.5% of adopted individuals had drug-abuse problems as identified by Swedish medical, legal and pharmacy records, versus 2.9% of people in the general population.
But 8.6% of those who had at least one biological parent who abused drugs had their own abuse problems versus 4.2% of adoptees whose biological parents did not have a history of drug abuse.
Adopted children had roughly double the risk of drug abuse if their biological full- or half-sibling had similar issues. But the risk was about the same if their adoptive siblings -- those who had no biological connection to them -- had abused drugs.
In general, trouble in the adoptive family, such as parental divorce, death, criminal activity, and alcohol problems was linked to a higher risk of drug abuse in the adopted child.
There are a number of things adoptive parents -- and biological parents for that matter -- can do to minimize the risk of their children experimenting with drugs