No. Regulate and offer known recreational drugs pure.
Very few people take fentanyl on its own or intentionally. Even tranq (which I hadn’t heard of but just looked up) is primarily harmful because it’s often tainted with fentanyl or other potent yet potentially fatal additives. Fentanyl does not need to be legally sold, because there is no real market for it.
Hell, even fucking weed is tainted, primarily with silica-based desccants, in countries where it’s still illegal (cough UK cough).
However if people could get pure, laboratory tested recreational drugs then these issues could disappear overnight. Heroin is bad when you fall deep into addiction, but most heroin users wouldn’t get into that state if they could take the drug legally without taboo or victimisation of illicit dealers. 100 years ago opium dens were a thing, and there were some people deep in the poppy - but there were also people just as deep in their alcohol suffering worse. Alcohol is less of a problem today, and back in the 90s there was a study funded by DARE (and subsequently unpublished because they didn’t like the results) that determined most heroin users were in fact business men and women earning large salaries with enough income to support their habit with high quality product.
Just like digital piracy is a service problem, drug addiction is a societal mental health problem, and criminalising it only allows the problem to fester to extremes.
Decriminalise possession, keep supply of the most fatally harmful drugs illegal, legitimise and tax known recreational drugs.