Studies of identical twins separated at or near birth show that if one sibling is affected, there is a better-than-average chance the other will be as well.
And research published last month found that youngsters exposed to very high levels of organophosphate pesticide, used on many commercially grown US fruits and vegetables, were also at greater risk.
But to date few large-scale studies have tried to isolate the potential impact of social and family influences on ADHD.
To help fill that gap, researchers in Sweden sifted through data on 1.16 million school children and examined the health histories of nearly 8,000 Swedish-born kids, aged six to 19, who had taken ADHD medication.
"We tracked their record through other registers ... to determine a number of other factors," said lead author Anders Hjern, a researcher at the Karolinska Institute in Stockholm.
The study, published this week in Acta Paediatrica, found that women who had only received very basic education were 130 percent more likely to have a child on ADHD medication than women with university degrees.
Living with a single parent increased the chances of being on medication by more than 50 percent, while coming from a family on welfare upped the odds by 135 percent.
Boys were three times more likely to be on medication, but these social elements affected both sexes equally.
"Almost half of the cases could be explained by the socioeconomic factors included in our analysis, clearly demonstrating that these are potent predictors of ADHD-medication in Swedish school children," Hjern said.
Lack of time and money are more common in single-parent families, as are family conflict and a lack of social support, he said.
Further research is needed to explore the intersection of genetic and environmental factors to devise better prevention strategies, he added.
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