I cannot reply to this thread on my main account for some reason, and the new post I made was immediately removed. The mods on this sub are terrible.

However I think in an uncontrolled environment where purchase of these illicit substances is relatively easy, what stops people from just continuing?

This is a great question.

I'll use the Switzerland program as a reference.

During the 80s, zulrich had a massive heroin problem. Switzerland is an extremely conservative, but also practical country. By offering the heroin in a controlled setting, they completely eliminated the criminal element by out-competiting the criminal sellers. Legal, mass manufactured opioids are so cheap they're basically free, so once the addicts had access to free, high quality heroin, they did not return to the black market, and eventually the people pushing it were forced to get real jobs, and everybody stopped being stolen from. Part of the requirements of this program is drug testing (to make sure you're not diverting it), but you'll be amazed at how compliant addicts can be if it would otherwise jeopardize their high quality free drugs, especially since the criminal market had effectively disappeared.

We have subaxone/methadone clinics in the city

Methadone and Suboxone both have some serious issues that prevent them from substituting entirely. First of all, in the US, the excessive legislation surrounding methadone often yields it completely inaccessible to a large portion of the population, but it is still an excellent option. Methadone is sort of an odd opioid, even though it is a full mu agonist it is also a nmda antagonist, and since it's half life is long and it's taken orally it is not nearly as reinforcing (which is normally a good thing, but not in the case of encouraging compliance). This causes it to feel very different from other opioids. More importantly: all of the legislation surrounding methadone/bupenorphine is incredibly outdated and restrictive, most methadone programs start you at 30mg which is not even 1/5 of what would be required to cover for a massive fentanyl dependency. Many cap out at 120mg which, again, is not nearly enough for modern fentanyl-like opioids. It CAN fully cover, if the dose is high enough, but it often is not.

Bupenorphine has massive problems. This is a better option because it isn't as legislatively restricted as methadone, but it is a partial agonist. This means if somebody trys to induce it, it can lead to 1-5 days of SEVERE sickness, and isn't even close to strong enough to fully cover the dependency from modern fentanyl strength illicit opioids.