Gambling on marijuana use makes for bad decisions

I just can’t seem to stay away from the marijuana debate, even given the recent defeat of Proposition 19 that aimed to legalize marijuana in California. This article is a short one, but speaks to some of the cognitive issues associated with marijuana use.

A study (see here) conducted by a Wake Forest University team (Including Doctor Linda Porrino) found that habitual marijuana smokers (those who smoked an average of twice a day for seven years) may be bad at detecting negative outcomes.

The experiment used fMRI scanning technology to examine the brain activity of smokers and controls during the Iowa Gambling Task, which uses four decks of cards. Two of the decks yield large, infrequent, rewards as well as losses. The other two decks yield small, more frequent rewards, and less losses. The first two are considered the “bad” decks, and the latter two the “good” decks, because selecting from the small-gain, small-loss, decks will result in more gain overall. The task is considered a pretty good, if complex, measure of risk-taking, decision making, and loss-discounting.

Marijuana users lose money while controls gainThe take-home result from the study: Not only did marijuana smokers take longer to learn how to maximize their rewards, but their decision-making brain regions seemed to show lower overall responding during the task, meaning they were less active while performing the decisions. And as you can see from the graph on the left, while the controls were able to achieve overall gains, the same was not true for the long-term marijuana users even after 100 repetitions. It seems that marijuana smokers’ brains were not as efficient at detecting losses and responding to them. Maybe that’s why marijuana users are the first to claim that marijuana use has no negative outcomes associated with it…

As usual, it is important to note that since the participants in the study were not randomly assigned to long-term marijuana smoking, it’s impossible to know if these deficits are specifically caused by marijuana use or if they were pre-existing. Nevertheless, these results strongly suggest that individuals who engage in long-term use of marijuana are cognitively distinct from those who don’t. I think that plays into the argument that marijuana legalization would not increase use, because if that’s actually true, then there’s something different about individuals who choose to smoke weed and it is not the legal status that matters. I suspect that in actuality, people who currently choose to smoke marijuana long-term are in fact distinct, in some ways, from some of the people who would take up smoking the stuff if it became legal.


Christopher T. Whitlowa, Anthony Liguoria, L. Brooke Livengooda, Stephanie L. Harta, Becky J. Mussat-Whitlowb, Corey M. Lamborna, Paul J. Laurientic and Linda J. Porrino (2004). Long-term heavy marijuana users make costly decisions on a gambling task. Drug and Alcohol Dependence, 76, 107-111.

6 responses to “Gambling on marijuana use makes for bad decisions”

  1. So the study is a bit more complicated then is being presented here. It’s not simply that the users made bad decisions, but “users made more decisions that led to larger immediate gains despite more costly losses than controls”.

    Sounds like classic risk taking behavior to me. Who would of thought illegal drug users would be more likely to take risks?

  2. I think that you’re right and that my first sentence (… may be bad at detecting negative outcomes), as well as my later explanation of the study detailed exactly that.

    This is indeed pretty much classic risk-taking behavior that is likely related to differences in brain function. Obviously, determining if those differences were the reason for the drug use, or if they were caused by it, is impossible given this study’s design.

    My point wasn’t to make a judgment, but rather report a recent finding on the topic.

  3. I’m sorry if I sounded rude, I’ve been compulsively debating about rush limbaugh on conservative forums tonight (some one should do a study on rush and dopamine release… hey his name is rush after all… we already know shock releases dopamine somewhere in the brain, right?)

  4. I always weigh in on the subject of long term weed use, because I have a lifetime of personal experience, and have had the opportunity to observe communities of long term smokers.
    I am the oldest of a family of 7 kids and two parents. My parents raised me in a way as to promote good family life with many kids, including lots of outside enrichment. (sports, the arts, and freedom that was earned with responsibility) My Dad and his family suffered many emotional traumas, and a serious brain injury, by the time I was 8 yrs old. He self-medicated, using weed (in those days it was very mild) and eventually everything started deteriorating. My parents soon found themselves in divorce mode, and my Dad’s personality was changing. He moved out, began getting high with my younger brothers and sisters, (they then found it difficult to attend school and very few even graduated hi-school), and I even began inappropriate gawking at me and cruising the hi-schools. Life was never going to be the same, and he thought it was all okay as long as he had pot to smoke. Later my brothers started smoking black tar, and using my Dad for money and housing. The entire family was ALWAYS fighting, and getting more and more manipulative as time went by. It’s just recently, that they have tried to recover. My Dad suffered another TBI, riding his Harley without a helmet, and has since passed as well as my Mom (who showed tremendous signs of just being worn out from all the damage done) Not saying, that’s everyone’s fate who chooses long term pot smoking…just sayin’ I’ve been around it all my life, and have yet to see a sustainable outcome. I don’t begrudge anyone’s usage, I just feel that our society needs to experience a few years of “Medical MJ” and see some real results, and evidence that pot doesn’t need to remain under at least minimum control, for the better of us all. IMHO

  5. Prohibition did not stop alcohol use it simply enriched those who sold it illegally. Those who want to use marijuana will whether it is legal or not. Some who would not otherwise break the law may be inhibited if it remains illegal.

    The real issue will be how people who use will become unproductive and end up with significant impact of their physical health. These losses in my opinion are not worth making it legal.

  6. Great information. Marijuana feels like one of those drugs where dependency can go on for decades. You are functioning, but at a much lower level than if you were not using. Your expectations for your life go down hill as well. As a parent, very difficult to watch, and to convince your child to go to rehab where people are addicted to the harder drugs. They don’t feel they belong there.

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