Drug Abuse Can Be Contagious

Drug abuse in a sibling or spouse increases the risk that an individual will abuse drugs

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) If Sally's brother John has a drug abuse problem, Sally is at risk for drug abuse too. But why? Is it more about the genes they share? Or is it about living in the same house?

A recent study attempted to understand this question a little better. It found that the family environment plays a significant role in the risk for a person developing a drug abuse problem.

An individual whose sibling or spouse has a drug abuse problem is at a higher risk for drug abuse, regardless of genetics.

"Seek treatment for drug abuse."

The study, led by Kenneth S. Kendler, MD, of the Virginia Institute for Psychiatry and Behavioral Genetics at the School of Medicine, Commonwealth University in Richmond, aimed to understand more about the environmental versus genetic contributions to drug abuse patterns in families.

The researchers used nine public databases to study 137,199 pairs of siblings and 7,561 pairs of spouses, in which one of the individuals of the pair had drug abuse problems. Drug abuse was determined based on a person's medical, legal or pharmacy records.

The researchers chose these groups so they could compare pairs who have a genetic connection (siblings) with pairs who are very close but not genetically related (spouses).

Overall, a healthy individual was found to be at a higher risk for developing drug abuse problems if a sibling or spouse abused drugs.

An individual who is born within two years of a sibling who abuses drugs is six times more likely to abuse drugs than someone without drug abuse in their immediate family.

However, if born ten years apart from a sibling with a drug abuse problem, the individual is only 4.5 times more likely to abuse drugs.

A similar pattern was seen with regards to drug abuse between spouses. Within the first year after a husband or wife's drug abuse problems was noted on official records, the spouse was more than 25 times more likely to abuse drugs than those not married to a drug abuser.

But five years after the first record of a person's drug abuse, a spouse's risk of developing drug abuse problems dropped dramatically to six times the risk of someone not married to a person who has drug abuse problems.

In other words, for both spouses and siblings, the more time there is between them or the more time there is since the drug abuse problem, the less likely it is that the healthy person will develop a drug abuse problem.

However, the closer siblings are in age or the less time that has passed since a spouse developed a drug problem, the more likely it is that the healthy sibling or spouse will also develop a drug problem.

These findings led the researchers to conclude that the family environment plays a large part in the risk of drug abuse regardless of any possible genetic factors.

Since there is evidence for genetic influences on drug abuse, the researchers said more research is necessary to understand what role genetics and environment each play and how they interact.

The study was published December 10 in the Archives of General Psychiatry. The research was funded by the National Institute of Drug Abuse, the Swedish Research Council, The Swedish Council for Information on Alcohol and Other Drugs and an ALF project grant from Lund, Sweden. The authors declared no conflicts of interest.

Reviewed by: 
Review Date: 
December 10, 2012
Last Updated:
April 11, 2013