The coronavirus pandemic is impacting the supply chain of illegal drugs, leading to new overdose risks, experts tell NPR.

Normal transit routes through South America or Asia have shut down, according to Uttam Dhillon, acting administrator of the U.S. Drug Enforcement Administration. There also has been a large drop in car and foot traffic to and from Mexico, the main source of heroin in America.

Addiction treatment specialist Joseph DeSanto of Orange County, California says many of his patients have found new sources of heroin and opioid pills. “When they had to use another dealer, they would be getting a different strength. So they weren’t really sure of how they should measure it and how much they should use. So we started seeing a lot of overdoses and a lot of overdose deaths in the first couple of weeks of the pandemic,” he said.