"To see the proportion of overdose deaths increasing to over 50 percent in 2016 is very alarming", said Brandon Marshall, assistant professor of epidemiology at Brown University and one of the study's authors.
The synthetic opioid is typically prescribed to help cancer patients manage pain, but in recent years, illegally manufactured versions have been sold as counterfeit pills and as a filler in heroin and cocaine to boost the drugs' potency.
New Hampshire trailed West Virginia with 34.3 deaths per 100,000 population, but saw the biggest increase from the prior year, when the rate was 26.2.
The study, published Wednesday in the International Journal of Drug Policy, provides another sign of fentanyl's dramatic rise in overdose deaths.
Many believe providing more access to the drug will help stabilize the rate of deaths related to overdoses, including Dr. Thomas Frieden, M.D., CDC director, who penned an opinion piece in Fox News late a year ago about ending the epidemic.
State health officials say they plan to develop guidelines about responsible opioid prescription practices, expand access to treatment and increase distribution of naloxone, a drug used to reverse overdoses. "We need to focus our overdose prevention efforts in younger people now", he said. Opioid addiction is one of the most hard to kick, and the most unsafe to have.
"Drug abuse is crippling families and communities throughout our country", Rosenstein said at a joint news conference with Drug Enforcement Agency officials. Opioid painkillers can slow and stop breathing, which is why they carry a high risk compared to other drugs - and fentanyl is a particularly potent opioid.