Good question, and well stated.
I am the first to admit being a terminology geek.
I say "pharma" of any kind today implies overwhelming benefit compared to risk in making a disorder measurably better, and I expect doctors and pharmacists to know this better than me.
When it comes to solvents though, and materials much more toxic than appear in the pharmacopeia, I do have an unfair advantage in direct experience and decades of intense study for the most part.
Substance abuse or addiction is possible whether or not the substance is really a drug or even very toxic or responsible for physical dependence.
I guess my point is that people can use things, and develop a dependence of many different kinds, like they were a drug even if they are something as simple as a common solvent.
Availability may mean more than "drug seeking behavior" a lot of the time.
Sometimes it's straightforward toxicity-seeking.
Chemically, solvents are usually very simple industrial chemicals compared to the vast majority of true drugs, especially the drugs in the PDR which are mostly carefully crafted for particular patients, rather than general consuption (like beer or liquor) or non-consumption which is how I scientifically categorize the solvents overall.
When I see people treat drugs no differently than alcohol, or alcohol no differently than drugs, I just don't think that is the most realistic treatment.
Once again, I'm not the expert on metabolism but I do think the metabolic effects are far too dissimilar also.
Disclaimer: my first job was with a drug manufacturer, I got there after paying my way at the university giving chemistry lessons to pre-med students, but that's as far as I went in that field. Solvents OTOH, I've been handling and directly observing their effects for decades since.