Toddlers of women who used methamphetamine in pregnancy, who live in an unstable home environment, appear to have an abnormal response to stress, a new study suggests.

Methamphetamine stimulates the nervous system, and prenatal exposure to the drug could affect the development of a child’s stress-response system, HealthDay reports. If the child is repeatedly exposed to severe stress at an early age, it can further affect the stress-response system.

The study included 123 two-year-olds whose mothers used methamphetamine during pregnancy. The researchers evaluated the toddlers’ reactions when they were briefly separated from their mothers. Children who lived in stressful conditions at home—such as having a mother who drank heavily or suffered from depression or other mental health problems—did not experience normal increases in levels of the stress hormone cortisol.

“The lack of hormonal stress response that we observed in these children has serious implications, such as a greater risk for depression, anxiety and attention-deficit/hyperactivity disorder,” lead researcher Namik Kirlic of the University of Tulsa in Oklahoma said in a news release.

Children who had a more stable home environment had normal increases in cortisol levels when they were separated from their mothers. “It’s not the meth alone,” said researcher Barry Lester, Ph.D., Director of the Brown Center for Children at Risk at Women & Infants Hospital of Rhode Island and The Warren Alpert Medical School of Brown University. “It’s the combination of meth exposure and adversity after birth. We see other things coming into play—the mother’s psychological health, alcohol use, exposure to violence at home or in the community. The postnatal environment is hugely important.”

The study appears in the Journal of Studies on Alcohol and Drugs.