60,000+ people are overdosing in the US. The Fentanyl China is dumping into the US killed 20,000 people in 2016, up from 3,000 just a few years prior. By comparison, Cocaine killed 10,000, Heroin killed 15,000, and prescription opiods killed 14,000.

The reason it disproportionately impacts life expectancy, is because a lot of the people overdosing are young.

If you suddenly have 250,000 people under 40 years of age overdosing over five years, you're going to see it in the life expectancy numbers even if your population is 320m. The small increases you'd expect to see in life expectancy year by year otherwise, will evaporate.

To get a picture of the overall health impact (non overdose deaths), one would need to look at how many additional addicts the opioid explosion has caused (eg in the last 10-15 years), study the health impact over time on those people, and so on.