MORGANTOWN, W.Va. (CBS Local) — Fentanyl-related deaths have skyrocketed in West Virginia even as prescription-related opioid deaths declined, according to a new study.

Researchers analyzed the number of fentanyl deaths from 2015 to 2017 and found that deaths rose by 122%. Prescription opioid-related deaths decreased by 75% in those same two years.

The increase is partly blamed on illegal fentanyl imports from China, according to Gordon Smith, an epidemiologist with the West Virginia University School of Public Health and a researcher on the study funded by the National Institutes of Health.

Up until 2015, “people who were shifting from legal prescription drugs to illegal drugs were shifting to heroin and opioids coming in from Mexico and other places,” Smith said. “But then people started manufacturing fentanyl in China, setting up clandestine labs, staying one step ahead of drug-enforcement agencies.”

Fentanyl is 50 times stronger than heroin, according to the Centers for Disease Control and Prevention.

“The big thing about fentanyl — and now carfentanil, a fentanyl analog that’s a thousand times stronger than morphine and heroin — is that it’s very easy to export,” Smith added. “Instead of having to smuggle truckloads of heroin in, someone can send small packages through the mail.”

While West Virginia’s increase in fentanyl-related deaths is part of a national trend, the state leads the nation in that category and has the highest per capita rate of overdose deaths.