A new study suggests opioids may blunt natural parenting instincts. The findings may help explain why some parents who are addicted to opioids put their children at risk, The New York Times reports.

The researchers scanned the brains of 47 adults before and after they underwent treatment for opioid dependence. While their brains were being scanned, participants looked at pictures of babies. Their brain scans were compared with those of 25 healthy people who looked at baby photos.

Some of the photos were manipulated to make the babies seem more appealing, with round faces and big eyes, while others were made to look less appealing, with smaller cheeks and eyes. The brains of people with opioid dependence did not produce as strong a response to the cute baby pictures as the brains of healthy people. When the people dependent on opioids were given naltrexone—a drug that blocks the effects of opioids—their brains produced a response similar to those of the healthy study subjects.