Study finds no long-term negative cognitive effects from marijuana

From Raw Story By Eric W. Dolan
Wednesday, July 11, 2012

While cognitive performance is negatively affected by cannabis use, the negative effects appear to completely wear off within a month, according to research published in the Experimental and Clinical Psychopharmacology in late June.

“With the number of cannabis users both illicitly and licitly increasing, the question of any potential lasting impact from cannabis use is increasingly important,” Amy M. Schreiner and Michael E. Dunn of the University of Central Florida wrote in their study.

Numerous studies have found that cannabis use affects memory, attention, perceptual-motor tasks, and other cognitive processes, but studies on how long these effects last has been inconsistent. The studies were complicated by the fact that psychoactive compounds in marijuana can linger in the body for days.

In hopes of better understanding the long-term, lasting effects of cannabis use, the researchers used a meta-analysis, a statistical procedure that allows researchers to mathematically summarize the results of a number of different studies.

Schreiner and Dunn’s study included two of these meta-analyses. The first was comprised of 33 studies that examined the cognitive effects of cannabis use after intoxication had worn off. The second was comprised of 13 studies that also examined the cognitive effects of cannabis use after intoxication had worn off, but this group of studies tested users after at least 25 days of abstinence.

The study found that cannabis use caused small impairments in attention, learning, and other cognitive processes that persisted after intoxication. However, the researchers said it was unclear if these minor impairments “translate[d] into practical impairments in functioning.” But the second meta-analysis suggested that these minor impairments don’t last longer than a month.

“While the first meta-analysis revealed a small significant negative effect for general performance and a number of cognitive domains, the clinical significance remains unclear,” Schreiner and Dunn explained. “A second meta-analysis focusing on studies with longer abstention periods was conducted and indicated no lasting residual effects on neurocognitive performance as a result of cannabis use… Whether differences seen in the initial days or weeks of abstinence are due to drug residue effects or withdrawal effects, after approximately 1 month these effects do not persist for the moderate to heavy user.”

2 thoughts on “Study finds no long-term negative cognitive effects from marijuana

  1. I’m a schizophrenic.
    I use cannabis to treat it even though this is not recognized as a reason for medicinal.
    Since my last appointment
    I am now in the recovery phase and am being weened off of my anti-psychotics. I’m living proof that marijuana has absolutely no negative side-effects on schizophrenia and that in fact it is probably one of the best treatments for it or at least for the depression that goes along with it. All arguments about that aside, prohibition is extremely dangerous to us. Most drug users are mentally ill and self-medicating statistically. When you are busted and put in jail/almost put in jail it can cause someone to have a psychotic episode and attempt suicide. I’ve been there when I was at my worst. One time the police even left a noose in my car even while knowing I have a history of suicide attempts. One of the biggest reasons prohibition needs to end is because it makes martyrs out of people who are either mentally ill or who just have addictions. I hope in time we can move forward as a society and see why it is wrong to criminalize the people you claim to want to protect and I just hope that nobody does end up taking their own life in this situation. I’m lucky to have survived and recovered throughout this. They’ve made my life a living hell up until this point.


    • God bless you Michael. Excellent points you have made, we seldom hear about the risks of suicide and worsening mental illness as a result of prohibition. Thank you for sharing this testimonial. Of you ever feel like writing a short (?) piece for this blog about how cannabis has helped you, we would love to print it! You could leave it here as a comment.


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