The debate over marijuana continues apace, with two new New York Times articles (here and here) discussing the increased potency of contemporary cannabis and its implications for addiction and speculative legalization. (Tellingly, these articles were in the "Fashion and Style" and "Opinion" sections, not "Health" or "Science").
I express no clinical or other opinion here about the issue, but merely report what I've observed about patient reports of marijuana in 15 years of general psychiatric practice, both inpatient and outpatient (I do not subspecialize in substance abuse issues, but the matter of substances comes up frequently in general practice).
In working with addicts one expects to encounter denial or, at best, ambivalence about the impact of substance use, but nonetheless I have met numerous patients over the years who fully acknowledge, whether spontaneously or when pressed, that their use of alcohol, cocaine, opioids, or amphetamine is problematic or destructive. However, I can probably count on the fingers of one hand the number of people I've worked with in 15 years who could be brought to see their marijuana use as dysfunctional (I mean, to really and painfully see it, not to vaguely humor me in considering the notion). To be sure, many patients suffer consequences from the drug's illegality, but that doesn't really count in assessing its dangerousness. Tobacco smokers on average are far more alarmed about their habit than pot smokers.
Again, I mention this not to condone its use, whether personally or professionally, but to wonder at what a strange drug it is. Its detrimental effects, such as they are, must therefore be insidious in the extreme, and not such as to disrupt life on a day-to-day basis. Indeed, more than with any other drug (even alcohol and tobacco), marijuana users tend to justify their habit as being calming and therapeutic (although some report that it makes them, if anything, more anxious). Many see it as a kind of alternative medicine, not so much different from taking St. John's Wort or other herbal preparations. If marijuana deprives its users of what would otherwise be a better pot-free life, it does so in such a way that they are unable to see what they're missing. To be sure, all addictive substances do this to a degree, but pot seems to do it more than most.
Laura Miller at Salon reviews a book by Ryan Grim called This is Your Country on Drugs: A Secret History of Getting High in America. I haven't read the book, but the article suggests that a central theme is the ubiquity of mind-altering substances throughout history and various cultures. This suggests that a central characteristic of consciousness is a desperate need to be other than it is; many accomplish this by means of other human beings, the arts, or God, but for many, directly biological self-management is too tempting to avoid altogether. Substances can and should be managed and regulated, but any attempt to suppress their use altogether may have unintended consequences, as the review suggests.