A new study suggests that women’s use of marijuana in pregnancy may predispose their children to an increased risk of anxiety, aggression and hyperactivity.

Researchers followed more than 300 mothers and their children. When the children were about 6 years old, the researchers measured heart function and hormones levels during stress. They also surveyed parents about their children’s behavioral and emotional functioning.

Children of mothers who used marijuana during pregnancy were more anxious, aggressive and hyperactive, HealthDay reports. They also had higher levels of the stress hormone cortisol compared with children who were not exposed to marijuana during pregnancy.

“Pregnant women are being bombarded with misinformation that cannabis is of no risk, while the reality is that cannabis is more potent today than it was even a few years ago. Our findings indicate that using it during pregnancy can have long-term impact on children,” researcher Yasmin Hurd, Ph.D., director of the Addiction Institute at Mount Sinai in New York, said in a news release.