Monday, December 16, 2013

New Study Out on Marijuana Use & Memory

This is a press release that describes a paper to be published in the December 16, 2013 Schizophrenia Bulletin, so one should not attach too much significance until we see the paper.  It comes from Northwestern's School of Medicine:
Teens who were heavy marijuana users -- smoking it daily for about three years -- had abnormal changes in their brain structures related to working memory and performed poorly on memory tasks, reports a new Northwestern Medicine® study.

A poor working memory predicts poor academic performance and everyday functioning.

The brain abnormalities and memory problems were observed during the individuals' early twenties, two years after they stopped smoking marijuana, which could indicate the long-term effects of chronic use. Memory-related structures in their brains appeared to shrink and collapse inward, possibly reflecting a decrease in neurons.

The study also shows the marijuana-related brain abnormalities are correlated with a poor working memory performance and look similar to schizophrenia-related brain abnormalities. Over the past decade, Northwestern scientists, along with scientists at other institutions, have shown that changes in brain structure may lead to changes in the way the brain functions.
The press release also addresses the existing published evidence of a causal connection between early marijuana use and later development of schizophrenia:
The groups in the study started using marijuana daily between 16 to 17 years of age for about three years. At the time of the study, they had been marijuana free for about two years. A total of 97 subjects participated, including matched groups of healthy controls, subjects with a marijuana use disorder, schizophrenia subjects with no history of substance use disorders, and schizophrenia subjects with a marijuana use disorder. The subjects who used marijuana did not abuse any other drugs....

Of the 15 marijuana smokers who had schizophrenia in the study, 90 percent started heavily using the drug before they developed the mental disorder. Marijuana abuse has been linked to developing schizophrenia in prior research.

"The abuse of popular street drugs, such as marijuana, may have dangerous implications for young people who are developing or have developed mental disorders," said co-senior study author John Csernansky, M.D., chair of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine and Northwestern Memorial Hospital. "This paper is among the first to reveal that the use of marijuana may contribute to the changes in brain structure that have been associated with having schizophrenia."

Chronic marijuana use could augment the underlying disease process associated with schizophrenia, Smith noted. "If someone has a family history of schizophrenia, they are increasing their risk of developing schizophrenia if they abuse marijuana," he said.
 A sample group of 97 isn't huge, and the even smaller sample group of 15 marijuana users with schizophrenia is even more of a "suggestive rather than persuasive" connection, but 90% smoking pot before developing schizophrenia should make Americans a bit less enthused about the "marijuana isn't really bad for you" stuff that is now the dominant sentiment of the mass media.

On the other hand, if you don't mind that voters don't remember how badly the people they voted for last election screwed, then memory loss is a feature, not a bug.


  1. I don't see where it compares the . That 90% just compares heavy marijuana-using schizophrenics to all marijuana-using schizophrenics in the trial, which... isn't very surprising, since tending to extremes of consumption is a common pre-schizophrenic trait. This news report on the paper says that the total afflicted group involved 10 marijuana-using non-schizophrenics, 15 marijuana-using schizophrenics, and 28 non-marijuana-using schizophrenics. If those individuals were randomly selected, that might even tell us about the relationship between marijuana and schizophrenia --although it's weaker than your numbers suggest, with only 34% of the schizophrenics reported marijuana use (compare 10% of populace reporting marijuana use). But since the trial subjects pretty clearly weren't randomly selected, that may have a large number of confounding factors.

    The difference in brain structures and working memory tests are somewhat more meaningful, but without having the actual magnitude of difference, it's hard to tell whether they're trustworthy or meaningful.

  2. You raise a good point. Of course, if schizophrenics are 3.4x more likely to be marijuana users than the general populace, that would tie with other studies that suggest that while not the only cause of schizophrenia (nor has anyone claimed it), it is likely a contributing factor.

  3. Perhaps, but again, were they randomly selected from the populace of schizophrenics or of marijuana users, or even the general populace, or did the study's creator go out asking specifically for marijuana-using schizophrenics? The effects of the volunteer bias are non-trivial, and this is exactly the sort of situation where it'd be very serious.

    ((I wouldn't be surprised if there /is/ a link, but I'm skeptical it's this one drug that is so highly significant.))

  4. It appears that the study was concerned about a control group, which does not suggest that they were looking specifically for marijuana-using schizophrenics. Some of the longitudinal studies have concluded that regular marijuana use (several times a week) by young approximately doubled the risk of schizophrenia; others found that it increased risk by 1.4x. Obviously, if you are not a risk of schizophrenia because of genetics, marijuana is problem not terribly dangerous from the standpoint of schizophrenia. How confident are you that you aren't at risk?

  5. I work with this population in my second career as a corrections counselor. While I am firmly opposed to the use of illicit drugs such as marijuana & believe that it has deleterious effects, this particular study, with its small sample, brings me to question its conclusion & how it is framed. Early-onset schizophrenia (one doesn't just wake up one day & there it is) can drive some to seek to self-medicate, even though they can't exactly articulate their problem, with drugs such as marijuana.

    While I agree that marijuana can be a cause of such physical & psychological problems, the manner in which this study is laid out is questionable.

  6. Small sample is a serious problem, however, of the 15 schizophrenics who had smoked mariuana, 90% had started smoking before developing the illness. The longitudinal studies that have been done also have compared people with no prodromal symptoms of mental illness and found that marijuana appears to increase the risk of developing schizophrenia. (Of course, many people develop schizophrenia without marijuana use.)