I only see two practical answers to the fentanyl crisis. Legalize it, or total war against the suppliers.

Which one you pick will largely come down to personal morals or ethics.

The addictive properties of the drug and profits seem to make the responses of more mellow legal incentives -- inelastic. The addict does not give a shit he may go to jail. The high-level supplier does not care he might be risking life, when he is making a gazillion dollars and plans to go out shooting anyway. The low level suppliers, well they fall under the same problem as the 'addict' bucket because you can get as many as you need from that one, no matter the consequences.