The New York Times has a fairly extensive article on deaths by fentanyl. The writer acknowledges that their data is not as good as he would like, but the article does include a section describing the data collection process. And it's reasonable.
The estimate is that 62,500 people overdosed on drugs in 2016, most of whom died from fentanyl and similar drugs. Death from drugs is thought to be the largest cause of death for those under 50 years old.
The article also estimates that "Over two million Americans are estimated to be dependent on opioids, and an additional 95 million used prescription painkillers in the past year — more than used tobacco".