If you look at heroin and meth addicts, I think it's pretty easy to see that it's not only dependent on price (which for meth is quite cheap in some countries). A lot of addicts will in the long run be unable to hold a job because of their drug use, and will only turn to crime when that happens.
On meth: remember in the US this is a legally prescribed medication, and effectively indistinguishable from other amphetamines such as the Adderall mixture. There are plenty of professionals using amphetamines. The difference is probably that they're not smoking it for a rush, but using it to gain a long mental advantage. They're certainly very functional.
On heroin: Opiates are far less harmful than smoking, as long as you don't overdose (which is often caused by improper labeling or mixing with other drugs). You'd be surprised how many professionals are using opiates (such as time-release oxycodone) daily. Again, the difference is in using it for the mental advantage, not IV'ing it to get a rush and high.
It's just that in general, you're not going to have such people confess their usage due to negative social stigma. Thus the only "addicts" you see, are the ones that couldn't hold a job, couldn't get a supply (it's generally easier to buy heroin than proper opiate pills), and so on.
Well, I think that a big part of those "functional" users are like functional alcoholics. They continue for many years to hold a job, but their daily usage causes problems for everyone around them.
At least that's the story you'll often hear at family group meetings. Not the usual homeless drug addict story, but people keeping up appearances while hiding some pretty big problems.
My brother was a functional meth user for many year before he lost his fiancée (mostly because of the anger outbreaks and lies, we didn't know he was using then), then his license and car, and finally his job. Of course then again there may be far more people that just continue using without ending up in the same situation.
Well, I'm just gonna say arguing anecdotally is pointless. However, functional opiate and amphetamine users are not "hiding a big problem". In many cases, this is enabling them to deal with high-stress situations, or think more clearly. One example is Paul Erdős, a brilliant mathematician that used amphetamines quite a bit and found no reason to not use them. No hiding, no problem, no "keeping up appearances".
Don't by into the "addiction is bad" story that DARE and the like sell.
While I've had a very liberal view regarding drugs and certainly not bought into any campaign stories, I've also become much more respectful about their potential consequences in the past years from firsthand experience. It would be interesting to see more about how prevalent drug use is. I do think you underestimate the negative consequences they can have. Drugs like meth and cocaine don't just cause the users to think more clearly, it can also cause some big behavioral changes. For instance, it's not far-fetched that the economic crisis has been at least partly been caused by overconfidence from drug use: http://www.theguardian.com/business/shortcuts/2013/apr/15/co...
