Using actual evidence to discuss cannabis


As more states and countries begin to engage in the issues associated with marijuana prohibition, it’s important that lawmakers and citizens alike have the best possible information to be able to make wise decisions in public policy and in our everyday lives.

We don’t know everything about cannabis yet. After decades of inactivity in the U.S., it needs serious, objective study. That said, it’s pretty frustrating to see some of the often-repeated crap being produced on the subject today. In too many cases, it appears that the difference between “causality” and “link between” aren’t part of the journalistic pallet anymore. If there’s a link, there is cause.

That’s why I’m encouraged by a recent series of reports released by the International Centre for Science in Drug Policy, and I urge everyone interested in the subject to read at least the summary if not the entire report. The group of scientists investigated the 13 most repeated claims on cannabis use and then tried to determine if there were evidence to back them up. What they indicate is that there is little verification to back up most of the declarations that have become almost rote fact by now from sheer repetition.

Number one on my own list is that cannabis can lower your IQ by up to eight points. I see this one constantly, especially when the discussion centers around youth and marijuana use. It’s a horrifying suggestion designed specifically to evoke the fear of god in a parent. But what the researchers found is that scientific evidence that suggests cannabis use is associated with declines in IQ is lacking.

As it turns out, almost all the headlines refer to one 2012 study that used an earlier study “to test the association between persistent cannabis use and neuropsychological decline and determine whether decline is concentrated among adolescent-onset cannabis users,” according to the abstract.

Now writing a news story or headline that states that anything lowers IQ based on one study is problematic, but in this case, it’s especially so. Even the study’s author urged caution in interpretation. A tiny sample (38 people, representing 3.7 percent of the total study) doesn’t really come up to the level of “Cannabis Destroys Brain Power and Lowers IQ” (Daily Mail) or “Study Shows Heavy Adolescent Pot Use Permanently Lowers IQ” (Forbes). (And what the hell is “brain power” and how is it quantified, anyway?) 

Researchers trying to duplicate the same experiment a year later found that the earlier study hadn’t taken other socio-economic factors into account. The researchers also found a recent, larger study that found that alcohol use was associated with declines in IQ.

“Our findings suggest cannabis may not have a detrimental effect on cognition, once we account for other related factors, particularly cigarette and alcohol use,” said researcher Claire Mokrysz of her 2013 attempt at duplication. “This may suggest that previous research findings showing poorer cognitive performance in cannabis users may have resulted from the lifestyle, behavior and personal history typically associated with cannabis use, rather than cannabis use itself.”

Another one I come across a lot is that cannabis use impairs cognitive function. On this one the results were inconclusive: The researchers found studies that offered moderate evidence that early onset and sustained use is associated with impairments and cognitive function but also found gaps in the evidence on the full range of effects.

“Given the current state of the scientific research, the simple assertion that cannabis leads to reduced cognitive function is misleading,” they write. “It’s also noteworthy that a systematic review of all longitudinal scientific studies on this topic found that the evidence did not support a causal relationship between cannabis use by young people and various psychosocial harms.”

Another big claim I read about a lot and is currently listed on the SAM (Smart Approaches to Marijuana) website is that cannabis use, according to founder Kevin Sabet, “can result in serious, long-term consequences, like schizophrenia.”

The researchers found some studies that point to a link between cannabis use and “the risk of symptoms associated with schizophrenia” and a more recent one that came to the opposite conclusion.

And, they note, if cannabis “caused” schizophrenia, we would be seeing those increases in the population as cannabis use rose, but that has not been the case. Research suggests that young people predisposed to schizophrenia may have their risk increased by using cannabis. That’s hardly the same as Sabet’s dire warning.

Lesson: If you’re interested, read all you can about cannabis, but be skeptical of everything, too.

You can hear Leland discuss his most recent column and Colorado cannabis issues each Thursday morning on KGNU.

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