New US research has found a link between taking certain medications for Attention Deficit Hyperactivity Disorder (ADHD) during pregnancy and an increased risk of birth defects in children.

Carried out by investigators from Brigham and Women's Hospital (BWH) in collaboration with investigators in five Nordic countries, the team used data taken from multiple large cohorts to see if taking the most commonly used ADHD medications during pregnancy could have an impact on the risk of birth defects.

Prescribing medications to treat ADHD is becoming increasingly common, but there is little evidence available on whether exposure to these drugs during early pregnancy may increase the risk of birth defects. However, animal studies have previously found that very high doses of amphetamines could potentially increase the risk of heart defects and other birth defects.

To look into the safety of these drugs for humans, the team used data taken from 1.8 million pregnancies in the US, with more than 2,700 of the women filling a prescription for methylphenidate during their first trimester of pregnancy, and more than 5,500 filling one for amphetamines.

The findings were then validated using data from a cohort of 2.5 million pregnancies from Nordic registries.

Based on both the populations, the team found that overall, exposure to methylphenidate during the first trimester resulted in a a 28 percent increased risk of heart malformations, corresponding to three additional infants born with congenital heart defects for every 1,000 women.

However, no association was found between methylphenidate and congenital birth defects overall, or for amphetamines and any congenital or heart defect.

"This information may be important to patients and their physicians as they weigh the risks and benefits of alternative treatment strategies for attention deficit hyperactivity disorder," commented corresponding author Krista Huybrechts, PhD, of the BWH Division of Pharmacoepidemiology and Pharmacoeconomics. "Our study markedly expands the evidence base regarding the safety of methylphenidate use in pregnancy," said Huybrechts. "Although the absolute risk is small, it is nevertheless important evidence to consider when treating young women of reproductive age and pregnant women."

Their findings can be found published online in JAMA Psychiatry.