Rather than solving this issue with technology, I think policy is the way to go here. If drug use was less stigmatized and not criminally punished, people who feel they are using too much drugs don't feel afraid of seeking help, allow us to reach them quicker and earlier.
I would just note that there are very few deaths related to drugs in Japan. It's possible to control. Though I suppose that doesn't include the issue with alcoholism. Still, I feel like it makes sense to stigmatized something that is dangerous and quite unhealthy.
In Japan, you go to prison, years, for having cannabis traces in your piss. Then you get deported for good. And say goodbye to your Japanese family cause you will not get a visa anymore.
The technology already exists: as other people have pointed out you can get test kits for fentanyl pretty cheap. And that applies to almost every drug too, you can buy Marquis reagent which covers most commonly used recreational drugs. But people really are not used to the idea of testing their drugs: when was the last time you bought a shot at a bar and tested it to see if it contains methanol, or checked if aspirin from your pharmacy is actually aspirin?
We don't really need to change an entire society, all we need to do is legalise and regulate recreational drugs. That immediately solved the problem of missold drugs. The societal stigma which prevents people seeking help for addiction might not vanish overnight but it's impossible to do anything about it while drugs like opioids are illegal.
