Doctor giving woman a prescription for her child

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TRONDHEIM, Norway — A child’s birthday may reveal how likely they are to take ADHD medication. A new study finds the youngest children in school — meaning that they’re born later in the calendar year — are significantly more likely to receive an ADHD diagnosis and start taking prescription drugs.

Researcher Christine Strand Bachmann from the Norwegian University of Science and Technology led a team that examined all Norwegian children born between 1989 and 1998. That’s a population sample of 488,000 people. They reviewed all prescriptions these children received starting at the age of 10 through their 23rd birthday.

Specifically, the team looked at children born between January and February and those born between November and December.

“We found major differences in the prescription of ADHD medication. Children born in November-December had an 80 percent higher risk of being prescribed ADHD medication, compared to those born in January-February. This finding applies to children who were born at term,” says Bachmann in a university release.

“I think the increased ADHD medication for the youngest children in the cohort has to do with the way we organize our education system. Put simply, it looks like we’re medicating the most immature children because we’re comparing them to their oldest classmates, who are a whole year older,” Bachmann continues.

“This shouldn’t be the basis for receiving an ADHD diagnosis. We have to expect that a child born in November is going to be less mature than a February child born the same year. Of course we can’t stop diagnosing ADHD and giving medicine to those who need it. But what we see here is something else.”

Premature birth can also increase ADHD medication usage

The team also discovered that ADHD drug usage was higher among children born prematurely — meaning before the 37th week of pregnancy — in comparison to their peers born at term.

“In that sense, the youngest premature children carry a double burden. The disadvantage of being born late in the year comes on top of the disadvantages of being a preemie,” explains Bachmann, a pediatrician at St. Olavs Hospital.

Overall, however, the tendency to need these medications was the same among premature and full-term children. A child’s birthday turned out to be the greater factor in determining ADHD medication use.

As children get older, premature children do experience another negative effect. The study finds ADHD prescriptions decreased with age among full-term children but stayed the same among preterm patients prescribed ADHD medications during childhood.

“It would appear that children who were born prematurely are extra susceptible to the persistent negative effects of being the youngest in the school environment. Perhaps they experience falling short in the classroom, in gym and in social contexts, compared to their peers. And perhaps the negative experiences settle in the body in a different way and to a greater extent in those born prematurely,” the researcher says.

Should younger children start school a year later?

ADHD patients typically deal with concentration difficulties, hyperactivity, and impulsivity issue which are beyond what is normal for a person (or child) of that age.

As for what causes some children to develop this condition while others don’t, the researchers say their findings point to an issue when younger children enter the school system — not a problem in their own homes.

“We have little reason to believe that the upbringing is different in families with children born late in the year, or that families with better childrearing conditions consciously plan to have children early in the year,” Bachmann says. “The findings indicate that the school situation is the cause of excess ADHD diagnoses. One solution could be for the children in question to wait to start school until the following year.”

So, should children with a later birthdate start school a year later than their friends born in the spring and summer? In some countries, like Denmark, this is already a common practice. In fact, 40 percent of school students born between October and December enter school the following year.

“In Denmark, parents and kindergartens are involved in assessing a child’s school readiness. I believe we could do something similar for our youngest children in Norway. Premature babies born late in the year could especially benefit from this approach. Some of them would actually have started a year later if they had been full-term,” Bachmann explains.

The researcher adds that children in Denmark born later in the year did not show the same levels of ADHD diagnosis and medication use.

The same trend emerged among other drugs

Study authors note their findings also appear to apply to medications for depression, anxiety, psychoses, and even sleeping pills.

“We found the same age effect for several of these drugs as well. Clearly more children born late in the year are receiving this kind of medication, compared to the oldest ones in the class. This was the case for both full-term and preterm babies,” Bachmann reports.

“But later in adolescence, from ages 15-23, this inequality disappeared. Children who were born late in the year in this age group didn’t use more of these medicines than those who were born early in the same year. This also applied to the preemies.”

The data comes from the Medical birth registry of Norway, the Norwegian Prescription Database, and Statistics Norway.

The study is published in the journal Pediatrics.

About Chris Melore

Chris Melore has been a writer, researcher, editor, and producer in the New York-area since 2006. He won a local Emmy award for his work in sports television in 2011.

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