It's probably a very complex thing and both sides of the discussion can pick something to attribute for. For example, you can say that it's because of the opioid crisis in the USA and pretend that it's happening in isolation - just some bad actors doing bad things that don't have anything to do with anything else.
Hong Kong has one of the highest life expectancy of the world and a major contributing factor is high population density. Paramedics are able (and must) arrive within 12 minutes of an emergency call, which is probably the most important time to keep people alive. Doesn't mean Hong Kong is a decent place to live though.