Heroin withdrawal or intoxication doesn't appear different than any other intoxication with opiates from the outside looking in. Also one can be strung out on heroin (or oxy, or hydrocodone or tramadol) and never inject it.

https://www.scientificamerican.com/a...s-are-soaring/

To be fair there's a bit of interpretation and speculation, but if you look at the massive amount of potential years of life lost with kids ODing in their teens and 20s, it's a pretty clear link that opioids are at least one of the factors driving a decreased life expectancy, and a big risk factor for developing an addiction to opioids is getting prescribed them in the first place... if you wanted to disagree with that statement you could probably find a good rationale, a lot of "does association equal causation" arguments would be valid.