The recent fax (yes, they still call it this despite it arriving via email attachment) from CESAR (Vol 21, Issue 40; October 09, 2012) puts us back on an occasional theme of this blog.
They have adapted data from the latest update from SAMHSA’s National Household Survey on Drug Abuse. This figure shows the number of past year users of selected illicit/recreational drugs.
Interestingly, marijuana use continues to trend up from the approximate plateau of 2002-2007, while use of cocaine is trending downward. Even the nonmedical use of prescription drugs (which has been a big problem overdose-wise) is relatively flat. Rounding slightly, we’re looking at some 30 million past year users of marijuana compared with 4 million past year users of cocaine.

So why is this interesting? Well, as we’ve covered in the past the notion of conditional probability of dependence is a key issue for parents and policy makers and yet we have really poor estimates on that. Direct studies are usually limited in scope and the big-scale epidemiological stuff is too imprecise- i.e., rarely are there good diagnostics of dependence. So we sometimes have to infer things based on, e.g., daily use rates versus annual rates. Something like that. Fortunately the more precise studies and the broader interpretive efforts tend to agree.

Roughly speaking the conditional probability of alcohol dependence is on the order of 4%, for cannabis on the order of 8-10% and for stimulants, including cocaine, on the order of 15%.

So, applying these rough estimates to the past-year data above, we end up with something on the order of 600,000 dependent on cocaine and 2,400,000 dependent on marijuana. If you dropped the estimate of conditional probability for marijuana to the 4% of alcohol, you still end up with 1.2M people dependent on marijuana.

My point, as always, is that the definition and scope of a “drug dependence problem” is going to depend on frame of reference. One important frame of reference in my view is the number of people who are affected. This, btw, is why we think of alcohol dependence as such a huge problem even though just about every estimate suggests the conditional probability of dependence is one of the lowest. Because the percentage of the entire population exposed to alcohol on a regular basis is so large, the number of people who are dependent is relatively large.

New Scientopians!

October 8, 2012


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