Addictive is the argument in favor of making it over the counter. Addicts will do whatever it takes to get their fix, so if there isn't a legal path, they buy on the street, creating a funding source for organized crime and spurring gang violence.
Then, because the black market is already in violation of the law, there are no purity standards. The customer who thinks they're getting Adderall or codeine is actually getting fentanyl because fentanyl's much higher potency makes it easier to smuggle, but for the same reason makes it much more prone to addiction and overdose, especially when careless street dealers get their proportions wrong. All of which is avoided if you just let them buy it from the pharmacy.
Notice that there is no thriving black market for antibiotics propping up international drug cartels, because they're not addictive.
> Addictive is the argument in favor of making it over the counter
You want to control the general population’s access to physically-addictive substances to control addiction. Managing addicts is not a pharmaceutical matter.
Strongly agreed, with one correction: black markets are driven by shortage. The role of addiction is in creating demand, and at the same time making authorities restrict access.
There is no thriving black market for antibiotics, because they are accessible when you need them (and most people need them very infrequently for a short duration). In contrast, I believe there is a black market for insulin in the US, and that's because of how ridiculously expensive it is. Exuberant pricing is a form of restricting access, too.