Children whose mothers smoked while pregnant were more likely to end up on medications such as antidepressants, stimulants and drugs for addiction, according to a study from Finland that hints at smoking's affect on a baby's developing brain.

While the findings don't prove that cigarette smoking during pregnancy causes changes in children's brains or behavior, they offer one more piece of evidence that should encourage women not to smoke while pregnant, the researchers wrote in the American Journal of Epidemiology.

"The exposure was significantly associated with the risk for all medication use and for both single- and multiple-drug consumption even after adjustment (e.g. mothers' severe psychiatric illnesses," wrote lead researcher Mikael Ekblad, at the Department of Pediatrics at Turku University Hospital.

"These findings show that exposure to smoking during pregnancy is linked to both mild and severe psychiatric morbidity."

Ekblad and his colleagues used Finnish data for 175,000 children born in the country between 1987 and 1989. At that time, midwives had asked all new mothers if they smoked during pregnancy.

The researchers then matched those birth records to a nationwide database of prescription drugs covered by insurance between 1994 and 2007 -- when the children were between five and 20 years old.

One in 11 children was prescribed a psychiatric medication at some point during that period, including anti-anxiety drugs, antipsychotics, antidepressants, stimulants and drugs for addiction.

Of children and teens whose mothers didn't smoke during pregnancy, 8 per cent were on at least one of those drugs during the study period. That compared to 11 per cent of those whose mothers smoked fewer than 10 cigarettes per day, and close to 14 per cent whose mothers had lit up more than 10 times a day.

The link remained when researchers left out babies who were born early or very small, which are other factors that could affect future mental health.

It also stuck when they looked at each class of drugs on its own, and was strongest for stimulant drugs that target attention problems and hyperactivity, and drugs for addiction.

The study is "entirely consistent with a large and still-growing research literature on the effects of prenatal and secondhand smoke exposure on the mental ealth of children," said Michael Weitzman, who studies that topic at New York University Medical Center and was not involved in the study.

"I find it very interesting and very important."

Exactly how smoking may change a growing baby or child's brain is unclear. It's possible that nicotine could affect brain development, or that access to oxygen during pregnancy might be reduced when the mothers smoke, the researchers said.

Weitzman, who said he thought the research was the first he knew of that looked specifically at the use of psychiatric medications in children whose mothers smoked, added that he thought it was "new and intriguing" that depression medications were also linked to smoking.

But the study had its limitations. Ekblad and his colleagues couldn't take into account whether the mothers had been on psychotropic medications themselves, or if they used alcohol or illicit drugs during pregnancy.

They also didn't know which fathers smoked while the children were in the womb, or if either parent smoked after the babies were born, when their brains would still have been developing.

Weitzman added that it can be hard to disentangle the effects of parental smoking during pregnancy from smoking when children are growing up.

"Very few women smoke just during pregnancy," he added.