A new study found drug use among teens increased their chances of carrying a firearm at school.

The study, compiled by Dr. Sonali Rajan of Columbia University and Dr. Kelly Ruggles of the New York University Langone Medical Center’s Department of Population Health, dissected data from 84,000 students from 2001 to 2011.

The students filled out surveys asking if they had carried a gun within the last 30 days, and the researchers analyzed various behaviors to determine if there was a connection. They discovered that while mental health certainly plays a role in gun possession among youth, fighting at school, and drug use were also powerful determining factors.

The researchers determined heroin to be the drug most associated with teens carrying a gun, but found cocaine, steroids, cigars, marijuana, alcohol, snuff, methamphetamines and other injected drugs to also be high on the list. They also discovered certain school behaviors, like getting in a fight or being threatened, increase the chances of a teen carrying a gun, but not as significantly as drug use.

According to Rajan, the best way to prevent gun violence is to place a stronger emphasis on a positive school environment.

“Our work takes [the recommendations] one step further and says we need to place an emphasis on the school environment, it’s not just about addressing mental health," Rajan said. "But from a public health and prevention standpoint...cultivating from a young age school environments where students feel respected by their peers and teachers and vice versa.”