The markets have been the main sources of the violence on the West Side, with some of the shootings linked to turf battles among gangs. Authorities announced the connection between overdoses and gun violence as they revealed the arrest of more than 50 people in a joint investigation by the police and the U.S. Drug Enforcement Administration. Guns, heroin, cocaine and methamphetamine were seized during the arrests. Chicago Fire Department calls for opioid overdoses on the West Side. They looked at cases in which paramedics administered a heroin-treatment drug called NARCAN.