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Do people really get addicted to marijuana?

Last week, the Los Angeles Times profiled a woman who was addicted to marijuana for 19 years, during which she used marijuana compulsively several times a day, experienced physical withdrawal symptoms, and spent as much as $5,000 a year to maintain her habit. A number of well-educated and successful people asked me in shock: "That story couldn't have been accurate could it? I mean, no one gets addicted to marijuana, right?" I have been asked similar questions over the years by top-flight journalists, respected scientists, Members of Congress and White House staffers.

This led me to contemplate an interesting mystery: How is it that over 4 million Americans meet medical criteria for marijuana abuse or dependence, yet many of the most educated and accomplished people in our society are not aware that marijuana can be addictive?

A cottage industry of bloggers and talking heads aggressively deny that anyone is ever harmed by marijuana, much as the Tobacco Institute used to deny any ill effects of smoking tobacco. But that's about ideology and not science: Among pharmacologists, the recognition that psychoactive drugs like marijuana can produce dependence is uncontroversial. And among treatment researchers and clinicians, it is a fact of life that many people seek treatment for marijuana addiction, including in countries such as the Netherlands where there is no legal pressure at all to do so.

In any event, I doubt pro-pot pundits affect the views of the well-educated professional class as much as does the "availability heuristic" a form of cognitive bias documented by the late, great Stanford psychologist Amos Tversky and his collaborator Daniel Kahneman. To reduce Nobel Prize-winning work to oversimplified form, we tend to think what we experience personally is more representative than it really is.

The normative experience of marijuana use for the educated middle and upper classes is to use it casually a bit in the late teen years and early adulthood. Many then stop using without significant effort or even thought, although some do remain occasional users throughout their lives. Most people in this well-tended segment of the population thus has used and seen other people use marijuana recreationally without apparent problems, and believes a la Tversky and Kahneman that this is the universal pattern.

But it's not. U.S. and International data tell us that about 10 percent of people who use cannabis will become dependent on it. The dependent population tends to use the drug every day, often several times a day. They have about three times the unemployment rate of the rest of the population and are disproportionately concentrated in lower income and minority communities (out of sight, effectively, to much of the middle class educated population).

Within the educated middle classes, some people do of course become marijuana dependent, and I will close by telling a story of this sort about a college friend whom I had forgotten about (I mentioned that advisedly) until I thought about writing this blog post. She began as a casual user and ramped up to once a day use and then all the time use. This is not a reefer madness story: She graduated and got a decent job and I heard later that she married a nice fellow. But for lack of a better term she slipped a bit. Her grades stayed okay, but not enough to keep her in the honors college. She did graduate, but it took her an extra 1.5 years, dropping her out of the circle of us who graduated on time. And we slowly forgot about her - leaving the availability bias to exercise its power and make us certain that lots of people at college were casual marijuana users and none of them suffered any ill effects.

In the race of striving middle class life, the alcohol or cocaine addict is the one who crosses into your lane and knock you painfully to the ground. You therefore can't fail to notice or remember them. The marijuana addict is the person who loses a few steps early on, finishes the race after you have showered and dressed and forgotten they were there standing next to you at the starting line.

Keith Humphreys, PhD, is a professor of psychiatry and behavioral sciences and addiction expert. He recently returned to Stanford after a one-year stint as a senior advisor in the Office of National Drug Control Policy in Washington.

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