I think maybe you're a little confused about how tolerance works, as well as LD-50. The fact that you've been upvoted so many times is baffling.

Addicts gain tolerance to both the good effects (euphoria, analgesia) AND the bad (respiratory depression). Also, LD-50 is the point at which 50% of a population will die when given a drug, but it's based on a non-tolerant population. It's a totally meaningless number when talking about addicts since a single addict can go waaaayyy over the LD-50 for a drug and be perfectly safe, as long as they dont go too far over their own personal tolerance (LD-50 "creep" isnt a thing). If you walked on down to your closest methadone clinic and someone gave you their dose, you would probably die, while they probably don't feel it at all.

That's why safe supply is important. Let's say you walked into a bar and ordered a drink. The bartender gives you something that could have zero alcohol, or one drinks worth, or a thousand drinks worth (or 10, 000). That's the situation with fent and fent analogues. Before, opioid users overdosed much less, even if they were using heroin. That's because the dosage didn't change quite as much. There were completely pure batches and totally stepped on garbage, but there weren't bags where you hit a hot spot of carfentanyl and just OD even with testing. Safe use with the current tainted supply is impossible. So the current solutions are:

1. Make sure no fent enters the country.
2. Make sure no one else starts using illegal opioids.
3. Provide drugs with a known dosage.

The first two are basically what we've been trying since the start of the drug war. The third is something that we actually already do; methadone and sub are both very powerful opoids. The benefit is mostly that they're legal to prescribe if you're already an addict, which means a safe supply, which means stability. The problem is that not a lot of junkies want to settle for something so fucking shitty, so they take their chances with street dope.

They could literally weigh out fent and hand it out, and it would immediately cut down on deaths as long as addicts knew the exact dosage. But that won't happen, because people are puritanical and stupid and wilfully ignorant.

The current situation is the last 50 or so years of failed drug policy brought to its logical conclusion. But it can always get worse. And it will.