A recent survey suggested that a majority of US respondents support the legalization of marijuana. The press release version from Angus-Reid Global Monitor is here. I've taken the liberty of graphing the data because something strikes me as funny.
It is very odd to me that the public view on drug harms seems to exist in a sort of good/bad binary state that does not appear to be graded with anything resembling a specific measure of "harmfulness" whatever that may be. If we may take the public willingness for legalization as a reflection of some global harm evaluation, that is. Some of the more philosophically defensible arguments, along the line of libertarian civil liberties and what not, would seem to be entirely independent of drug identity, right? So it must be something about the level of harm. The public appear to feel that there is a categorical distinction between marijuana and some other popular drugs but I just don't see where it is supported in terms of any given harmful outcome including risk of dependence, interference with ability to function when acutely intoxicated, acute risk of death, risk of toxicity to brain or other major organ with repeated use, etc.
Unfortunately, I was distracted by something shiny in my researches so we're going off on a bit of a tangent today...
These data come from the US National Survey on Drug Use and Health for 2008. They make the point that alcohol accounts for a very large swath of our abuse and dependence problem (defined by diagnostic criteria, as always, not necessarily reflective of what you consider a subjective drug problem). And as we all know, the majority of people who sample a given drug are never going to end up with drug dependence. Nevertheless data such as these illustrate a point I like to make about base rate. Namely that when considering the public health impact of legalization of recreational drugs we have to go beyond the rate of harm X and multiply that against the exposed population to end up with an estimate of eventual harm.
However, the much greater population prevalence of alcohol (91.5%) or cannabis (46.3%) in comparison with heroin (1.5%) means that the fraction of the entire population that is dependent on heroin (0.3%) is miniscule in comparison with the fraction dependent on cannabis (4%) or alcohol (14%).
To belabor my prior point, one of the reasons that a low harm rate drug like alcohol is such a big problem is that closing in on all of the population has sampled the drug in their lifetime. Some 96% of the US population have tried alcohol by age 27-28 and this reaches 98% by age 50 according to the current Volume II of the Monitoring the Future survey.
Shifting to more-proximal estimate of exposure, these data represent the fraction of the population (by age range) which claims to have had alcohol at least once in the past year, 30-days or daily over the past 30 days. Although not specifically shown here, the numbers for abuse and dependence are small enough to very likely be a small subset for most drugs. After this it gets tricky to evaluate from broad survey data like this. We'd want to know more about specific patterns of daily use and the history of those patterns if we were to attempt a finer grained prediction about risk for dependence. Nevertheless, I wanted to contrast these relationships for those for marijuana.
Note first the change in scale. (Normally I don't like to do that but for the sake of illustrating the point with low-res web graphics I caved in.) Many fewer people in the US population sample marijuana in a given 12-mo interval than sample alcohol. So the first point is that there is a lot of room for more people to sample marijuana under a change in access. Such as might be brought about by legalization such as was the subject of the survey I started the post with. This is the first untested (as yet) hypothesis. The second question is how the 12-mo / 30-day / daily and dependence rates scale up under such a scenario. If we compare to the legal substance alcohol, we might predict an under-predictive uptick in those who smoke cannabis on daily basis. OTOH, on face these data suggest a larger fraction of those who smoke cannabis on an annual or monthly basis smoke cannabis daily. Does this tell us cannabis is "more addictive" than alcohol given a particular rate of use? Or does it tell us that the untroubled user population represented clearly in the alcohol stats simply fails to smoke dope out of psychopharmacological preference or legal concerns?
I should point out that near daily cannabis smoking seems to be commonly associated with dependence, based on my chats with those who do research studies on human cannabis smokers. I also note that in at least one treatment seeking population of cannabis smokers, the mean was 25 days per month (Hathaway et al, 2009). I say this not because it rules in/out dependence for an individual but more to point out that there are people who smoke cannabis daily. This is news to some of my acquaintances who think cannabis is no big deal based on their college peer experiences.
I'll close with the lifetime stats for cannabis. As I said above, alcohol reaches about 98% of the middle adult population and the graph shows that about 65% have a drink at least once per month. The lifetime/monthly gradient for cannabis seems a bit steeper, does it not?
UPDATE 12/15/09: The first comment, from bsci, asked about cigarettes
Perhaps a better comparison would be nicotine, which doesn't have as long a cultural history as alcohol and currently has a great taboo regarding usage, even if it is legal.
so I'll graph those data as well. N.b., the survey includes an additional category for those that smoke a half a pack of cigarettes per day or more. Interestingly, it may be the case that only about 60% of those that smoke at least half a pack (or 10 cig) per day will meet dependence criteria (Donny and Dierker 2007). As you can see from these data some 83-89% of those who smoke cigarettes monthly, smoke daily. Similar numbers are 28-42% for marijuana and 8-17% for alcohol. The commenter bsci argues essentially that the casual use population is smaller for cigarettes because of social pressure, thus the prediction for marijuana should track these numbers. I'd argue that the difference between alcohol and cigarettes has more to do with perception of harm as it applies to self and accordingly, marijuana rates are not well predicted by the cigarette rates.
Johnston, L. D., O'Malley, P. M., Bachman, J. G., & Schulenberg, J. E. (2009). Monitoring the Future national survey results on drug use, 1975-2008. Volume II: College students and adults ages 19-50 (NIH Publication No. 09-7403). Bethesda, MD: National Institute on Drug Abuse, 305 pp. [pdf]
Substance Abuse and Mental Health Services Administration. (2009). Results from the 2008 National Survey on Drug Use and Health: National Findings (Office of Applied Studies, NSDUH Series H-36, HHS Publication No. SMA 09-4434). Rockville, MD. [pdf]
Cannabis dependence as a primary drug use-related problem: the case for harm reduction-oriented treatment options. Hathaway AD, Callaghan RC, Macdonald S, Erickson PG. Subst Use Misuse. 2009;44(7):990-1008.