The Russian Sci-Fi novel guy strikes back! I think it's relative hard to find a class difference in getting a treatment (as a Euro guy). But emerging side effects might be your thing.
There was an old story about an (illegal) drug (called
slegh, a fictional word) that was an unfortunate combination of perfectly legal components. In the original text it was like:
- if you plug a module for your aroma generator into your radio
- while lying in a bathtube
- and best if you chew on an anti mosquito aroma pill while doing so,
you'd get hallucinations that are so powerful, they are addictive. Folks keep lying in baths, at some point they stress their body too much and die. And no one tells outsiders what's happening, because, like, everyone does it.
(By the way, the story features some unconditional basic income, the philosophy of hedonism and consumerism, "let's destory this" demonstrations – hello red hot press from youtube, some kind of harsh immigration laws, gambling machines and what not. And it was written in the 60s!)
What can we learn from this? Mix your (legal) drug in, but make the undesirable side-effect of it a combination of several factors. Some of these factors would need to filter the target group.
- you need a radio to enjoy the genuine recipe of
slegh, but also that fictional smell adaption thingy (which I would guess was originally a radio lamp or a heterogyne);
- mixing antibiotics with alcohol, or, as mentioned in another answer, smoking;
- the plastic fumes of cheaper cars emits some smell ("of the car"), but also some more dangerous molecules, where the danger was not found earlier, as it persists only in combination with something else;
- one thing that might segregate the classes well is the availability and habbit of more exotic foods. Your drug might help to accumulate the fugu fish toxine, harmless elsewise;
- exposure to faster and more expensive ways of travel might be also a good separator. Let your drug induce the accumulation of radioactivity from full body scanners and flying;
- somewhat similar to bourgeois foods: Burgundy wine (for example) carries some endemic danger, that is exposed in combination with whatever (again, your drug, Rolls Royce leather seats, you name it), endangered are people who can afford such wines and locals. But most locals don't drive luxury cars.
I think you get the idea by now.