Hey.
I actually typed one hell of a long post yesterday morning in response to your previous post but decided to delete most of it (it wasn't flowing nicely and I kept getting interrupted for shit). If you have email notifications turned on you may have received a copy. If not: then just in case lemme try again.
As for being clean. Cocaine and Crack, ten year career, ended 1995 or thereabouts. Alprazolam, four year career (in fairness not totally to blame and can honestly say not mostly used for recreation i.e. overzealous prescription by my GP until we got to 12mg daily), ended 2010. Alcohol, always been around since like 1980, for recreational purposes obviously but not alcoholic i.e. mainly too many long business lunches and dinners and parties and a lot of binge drinking sessions, gave it up for fun (being facetious) beginning of last year. That's it really. Never been into anything else. Started 1mg - 2mg Alprazolam again most days (mainly at night) in April of this year (to date) in a crass attempt to keep my head together because of the havoc this fucking COVID caused in my life (but thinking it's time now to maybe give it up as a bad job as it's served its purpose). And the occasional Zopiclone at night. So I guess it depends on how broad your definition of the word "clean" is.

I guess my definition of "clean" would lead me to say "clean" for ten years. In those ten years: scored 1g of powder which was a waste of time and money. Scored 1 rock. Same thing. And about a six week stint on Tramadol ER last year (100mg per day) (due to sad circumstances).
The thread got me to thinking about something though (and mostly what my disjointed post of yesterday morning was about). As you noted: addiction is a complex issue. But this thread and my posting on it made me think of something. What's the difference between habit and addiction and dependence? At first I thought it was a dumb question. But if I look at my history of abuse as detailed: I've never craved anything ever. Crack obviously led to drug seeking behavior (chasing) during a binge session. But once a session was over: nothing. Other than of course looking forward to the next session (psychological). Same with powder. Same with alcohol. Benzodiazepine dependence was another story of course but not something I realized was happening until it was already a problem. And the most difficult part, after having tapered off after discovering that there was a problem, was giving up that last little sliver (was cutting pills to taper and toward the end was taking mere crumbs really i.e. at that point psychological only). Which by the way is the reason that whenever asked about this in the last few months I always tell people that if you're serious about getting off of them then calculate what you need to taper and toss the rest (because as long as they're in the house you'll never stop taking them). Dunno. Just got to wondering about all of this. But then again: fortunately I've never been attracted to opioids. And from what I gather: therein lies the difference.
Also found myself wondering if there's also not additional personality traits that all those that have the propensity to get addicted to things (and as we know: addiction isn't limited to substance abuse) e.g. depression, anxiety, being OCD about some things, you know what I'm saying. Now how much of the aforementioned can ALSO be attributed to genes: I know not. Would be an interesting study (if some have not already been done).
But the above really is why I was saying in my previous post that it's a monkey that'll always be on my shoulder and it is what it is. I mean I know I'm not capable of having a beer or two for the fun of it. Once I start: it's a bottle (or two or three) of spirits or nothing. Same during my Cocaine and Crack career. Either piles of the shit in a session or nothing. After all these years: cannot say I'm even remotely interested in going down a Cocaine route again i.e. too old and too many things have changed and a different mindset. Never used alone though and never just for the sake of it either. Only thing I do know is that it took a long time and a lot of changes to keep away from the shit. Had to eventually cut a few people out of my life because they were less than supportive of my resolve and it caused a lot of shit (they continued to use and use me because I was getting deliveries so used my spot to score and carry on in spite of knowing I'd had enough and was done). Had to avoid certain places too for a long while. And had to watch myself very carefully for a good long while when drinking so as to not start my shit again. Having said all of that: on the one hand I'm confident that if somebody used in front of me now and after all of this time I now wouldn't bat an eyelid. But on the other hand: knowing who I am it may just be a question of being in the wrong place at the wrong time and in the wrong mood and who knows. Hence my "monkey on my shoulder" comment in my previous post. Must admit: I always wondered, even felt bad maybe, for the longest while throughout all of this i.e. couldn't understand how come everyone else could go out to lunch (as an example) and have a glass of wine or two and that was that. My answer eventually came from the most unlikely of sources i.e. an interview with Ozzy Osbourne in a documentary made about him some many years ago. Not quoting him directly but the gist of it was that he said he was born an addict, never drank to be social, never shot Demerol to be social, he did it to get fucked up. Was a kind of light bulb moment for me really. No longer disliked myself after that. And oddly enough years later science took an interest in this and examined his genes and, well, the rest is history (I know I've posted this before but just in case it was missed here it is again and for sure backs up the genetic theory) (and this was a while ago so with advances in genetics pretty sure they'd discover even more):
Our genes might play a role in influencing who falls prey to addiction.
www.discovermagazine.com
Some interesting stuff in the article (and I've verified it using other sources i.e. it's not some fake news shit that didn't happen) if you read the whole article.
Of course there's an inherent danger in all of this (and in what I've posted). Without enough resolve: it could all be twisted and used as an excuse and as a justification to continue using (whatever your drug or substance abuse preference). That's the proverbial elephant in the room with all of this. Just something to be aware of I reckon.
As for designer drugs of the future:
I have a theory and which I posted about somewhere else around here some time ago and which oddly enough didn't receive the negative responses that I was expecting. With the current usual suspects (drugs) and what's being done to them, so far as I can tell from these forums, and based on personal experience even back in my day, would it be that far of a stretch to believe that at some point in time users will become so sick and tired of being ripped off and using unknown and harmful substances that all will revert back to natural substances? As I noted previously: this phenomenon saved my bacon anyway. And for the longest time, and in spite of not being a user, I've been a firm proponent of legalization of all substances. But I have to admit that after being a member here for a few months and thinking about things: I'm not so sure that it's such a good idea anymore. In theory it's a wonderful idea i.e. legalize, supply pure product under licence, use profits for rehab. centers and counselling, housing, and whatever else. But how is that going to stop the same thing happening as is happening now? As an example: what's to stop some lowlife dealer buying legit Cocaine, cutting it with fuck knows what, and reselling? Back to square one not? What about somebody like me? Am I sure that I wouldn't pop down to the local pharmacy knowing I could score an uncut gram? Just because I can? What about when it comes to drugs where the propensity to become physically dependent is high (I don't consider Cocaine as being such but that's just me)? Dunno. Just throwing out random thoughts here (and this from somebody that not too long ago was crowing from the treetops about legalization e.g. in the UK). I hear that it's working out nice in Portugal and Spain? But cannot help but wonder how many people in those countries are using now who would otherwise never have used or become addicts? Questioning my original stance on this type of thing now. Probably solves a lot of problems especially for those who are (were) addicts. But has it caused new problems? I don't know. Would it be fair to say that if somebody was going to use they'd use anyway and in the absence of legalization they'd make their own plan anyway? Are we not just talking about the lesser of two evils here? Dunno. Just thinking and/or typing out aloud I guess. And which I think I've done more than enough of in this post!
Anyway. There's my thesis for the day! Pretty sure none of the above is on topic nor of any help to the OP. Apologies.