On marginal utility of heroin street prices

| Pharma
Mark Kleiman points to this article about the enormous drop in the street price of heroin. Largely due to the ready availability of high quality Afghan product, the price is down to $90/g. Ordinarily, when the price of a product drops, that's good news for consumers of the product, but Kleiman claims otherwise:
The price of having a heroin habit, by contrast, doesn't go down much. Opiate tolerance is virtually complete, so in the medium term an addict's consumption is limited only by his ability to find cash; the cheaper the stuff gets, the more he uses, without getting any more pleasure out of it once his receptors have adapted.

I didn't know that opiate tolerance was that extreme, but I'm willing to take Kleiman's word for it. That said, I'm not convinced that what he says about the cost to users is right. At any given time, the amount of heroin you can take is limited by your tolerance (lest you overdose). This represents the upper bound. The lower bound is what it takes for you to get high all. Between these two points, there's presumably some pleasure/dosage curve with decreasing marginal pleasure per dose. Thus, if heroin is a lot cheaper, you'll tend to be somewhat more aggressive in terms of how much heroin you use, but it's still limited by the overdose point.

So, if heroin is a lot cheaper, you'll tend to develop tolerance somewhat faster, but there's still a maximum rate at which you can develop it, even if you have unlimited access to the drugs. So, cheap drugs extend the time during which you can afford to maintain your habit (before it exceeds your resources). In the limiting case, if drugs were free then you would never exceed your resources. As I understand it, users develop techniques for managing tolerance—detoxing in order to let their receptors recover, for instance—cheaper drugs would seem to reduce the frequency at which you had to do this, which, if you're a user, sounds like a win.