January 14, 2013
Long-Term Marijuana Use Could Have Zero Effect on IQ
Last summer, a study found that long-term cannabis use reduced cognitive skills. A new study seems to say the opposite. Image via Wikimedia Commons/Bokske
Last summer, a study published in the Proceedings of the National Academy of Sciences sparked a new round of worries about the dangers of smoking pot—especially for those who start smoking at younger ages. The study found that consistent marijuana use gradually eroded cognitive functioning and IQ, and with the legalization of recreational marijuana in Colorado and Washington, it’s made an appearance in a number of articles arguing that legalized pot poses a serious health hazard. Today, though, a new study published in the very same journal—and using the very same data set—suggests that the case against marijuana is a little less cut-and-dry.
Ole Røgeberg, a researcher at the Frisch Centre for Economic Research in Norway, analyzed the same survey results and found that the declines in cognitive abilities could be entirely attributed to socioeconomic factors. As a result, “the true effect” of marijuana use, he argues, “could be zero.”
Røgeberg is careful to note that his reinterpretation of the data doesn’t entirely discredit the original study, but he does write that its “methodology is flawed and the causal inference drawn from the results premature.”
Both the new and old studies draw upon a data set of 1,037 individuals from Dunedin, New Zealand, who were followed from their birth (either in 1972 or 1973) until they turned 38. At the ages of 18, 21, 26, 32 and 38, each of them were interviewed and scored for marijuana use. The original study found that IQ decline increased proportionately with cannabis dependence—especially for those who started smoking earlier on—and the authors concluded that using the drug was the cause of the decline.
Røgeberg, though, dug a little deeper into the data. He found those who started using marijuana during adolescence were disproportionately likely to have poor self-control and conduct problems in school—both factors that are themselves correlated with low socioeconomic status. In particular, members of the study with these traits were more likely to come from a Maori background, a group indigenous to New Zealand that has much higher unemployment, poverty and incarceration rates than the country’s population as a whole.
Numerous other studies have shown that low socioeconomic status adolescents are more likely to experience steeper IQ declines during adulthood. (Researchers hypothesize this is a result of being exposed to less intellectually stimulating environments.) As a result, Røgeberg wondered, could socioeconomic factors explain the IQ declines originally attributed to marijuana?
In his simulation, he tested whether socioeconomic environmental factors (dropping out of school, being exposed to less stimulating environments, and so on) could conceivably drive the same IQ declines reported in the group without turning to marijuana as an explanation. His statistical analysis found that these other factors could indeed completely account for the cognitive declines observed.
For support, he also points to a 2002 Canadian study that also asked whether long-term marijuana use impacted IQ, but with data entirely from middle-class survey participants. That paper found that IQ only decreased for current cannabis users, and when even heavy users stopped smoking, their IQ rebounded. Since that study largely excluded socioeconomic factors and did not find a permanent trend, he feels that it supports his argument that such factors play a major role.
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I started when I was 13, I am cosidered an over achiever, after hearing Lady Ga Ga in an interview when asked how do you write your songs, her reply was “I smoke a lot of pot” I knew that pot is still cool, on the “Golden Globes”, I`d say Terrentino was 420 happy……just sayin..=)
So all politicians that are so “concerned” about my health that they want to destroy my life (criminal persecution and criminal records) for my personal choice of what I want to ingest…
If they are really so concerned, they should be more concerned about my socio-economic status.
Especially all conservative politicians should, on the grounds of this research, conclude that it is not pot that is dangerous to public health, but income inequality. That should be prohibited, and the “war on income inequality” is what we need, instead of the war on drugs.
Our nation was founded upon freedom of the individual. Each of our citizens was guaranteed the right to the pursuit of happiness…so long as he brings no harm to his fellow citizens or their property.
When did this change?
I spent 5 years in Federal Prison for a marijuana offense.
And I am as harmless as a Beagle puppy.
I wrote about the escapades that led to my ‘extended vacation’…my book:
Shoulda Robbed a Bank
I would be honored by your review.
Please explain how low socioeconomic standing correlates to lowered IQ. Also: if the control group was this bad, how did the initial study even pass peer review and not get dismissed outright?
Harper already knows this. He had 2 company’s do study’s of the effects of pot, when they both came back saying a single joint was less harmful then a can of cola he threw it all out and destroyed what he could. but not before CBC reported it. (He he he) They know it’s harmless but don’t want to make it legal cause then they won’t make any money on them “MAKING” you sick. When i say they i mean the oil tycoons and pharma company’s. You know Harper’s bosses.
#4 asks how low socioeconomic status correlates to low IQ. One mechanism that’s hypothesized as leading to low IQ is that those that are quite poor experience a lot of stress (as they don’t have the means to meet their basic needs, etc.), this leads the body to release a lot of cortisol. This cortisol has a negative impact on the developing brain, leading to a lower IQ. Also, growing up as a member of a higher socioeconomic group means there are more opportunities for enriching experiences, which leads to enhanced brain development.
“The original study found that IQ decline increased proportionately with cannabis dependence—especially for those who started smoking earlier on—and the authors concluded that using the drug was the cause of the decline.”
Correlation does not equal causation. Jeeze, isn’t that the first, most basic thing researchers learn?
EVERY one of the children I know whose mothers smoked marijuana while they were pregnant are absolutely BRILLIANT!!!!!!! This FACT includes families from all walks of life – many living below the poverty line -
I am a grandmother who never enjoyed smoking marijuana myself – my own children were none too bright and one grandchild whose mother did not smoke marijuana is also none too bright……… but, the grandchildren of the marijuana smoking mother and many, many other children who I know personally born of marijuana smokers are OFF THE CHART, INTELLIGENT BEYOND MEASURE!
Whoever is doing this testing needs to figure out what they are doing wrong………
“how low socioeconomic standing correlates to lowered IQ?” As the poet says, “let me count the ways,” and they are nearly countless. Lead-based paint, for one thing; knowing how to take a machine-scored test, for another. Three million, the # of hits to google search on “socio economic correlates of IQ”. So, presuming you have the smarts to do, go do.
Social studies found that the greater the number of churches in a city the higher the crime rate. Therefore religion causes crime.
Right?
Right?
Wrong. The greater the number of churches, the denser the population, the higher the crime rate.
They have an observable fact, not a cause and effect relationship.
*Note that ‘IQ’ is largely a measurement of processes that are ‘learned’ & can easily be incorrect, eg try doing an IQ test in German one day & see how you score.
It’s like doing one of those ‘psychometric’ employment tests on a computer, If you’ve never used a computer before..
Having said that, I firmly believe that a certain level of mental ‘robustness’ is necessary to stop any drug altering intellectual capacity & rationality..
For whom are these types of questionable, incredible study results written? They are written for the already cognitively impaired who have no seeming ability to sift through barnyard materials and decide for themselves whether they are free men and women, or pawns for easy governmental control.
The millions of pages of good vs bad vs neutral cannabis studies help no one, except for the researchers who are vying for study funding. And who, and which study are we to believe? Already dubious at the outset, various studies’ results have a notorious history of wide, wild, and speculative outcomes for the individual, and for society. For example, the researchers of the study referenced above put forth two, TWO, competing outcomes, and other studies’ published results are at least as confusing and unbelievable as this alleged study. As a result of differing agendas, none of the results are credible.
Cannabis devotees use cannabis regardless of studies and don’t seem too concerned about long term use. Science and researchers have no credible evidence regarding effects of long term use, so their opinions are just like this article; so much hot air.
Whether this study’s first or second “result” is the correct one is moot. Cannabis smoke is gauged to be roughly twice as harmful as cigarette smoke. It carries toxins and is inhaled more deeply, and is kept in the lungs longer, than cigarette smoke. So lung cancer, among other things, is a distinct possibility for pot smokers. Bottom line, pot is not by any stretch of the imagination healthy for any individual. My personal opinion is that the laws legalizing pot were colossal mistakes. Now that the laws are passed, they may set a precedent for legalizing more dangerous drugs, which is yet another aspect of harm that voters in Colorado and my home state of Washington seem to have failed to consider.
Marijuana smoker’s IQ definitely reduces, and/or the accessing of cranial information is apparently decreased. Therefor, we hear the, “uh’s, duh’s, um’s” almost as often than a 4-year-old toddler stumbling on their words while learning how to communicate.
The comparisons of heavy users do not end with such speech patterns, however, as judgement is impaired and seemingly reduced because of the euphoric effect of cannabis smokers as well. Common Sense is reduced, when heavy smokers enter into a “silly phase” which is embraced and shared among “the party” group. Absurdities are far more embraced and often exhausted in conversation, especially in younger people. These parties often lead themselves, as a group, into bad judgement and bad attitudes, since that connection was previously made within a party group. Thus we have the rebellions and law breakers.
I read your article very interesting post. Good work. Keep it up.
I live in California. I do not smoke pot, but most of my friends smoke every day. Some of those friends are highly intelligent, and others are less educated and/or not quite as sharp. The pot smoking seems to have very little relevance compared to life experience.
Also, #13 and #14 are complete rubbish.