Which Strains of Marijuana Put the Least Strain on Memory?

By Andrew Moseman | October 5, 2010 1:11 pm

marijuanaCalifornia’s Proposition 19, a November ballot initiative to legalize marijuana, has fueled the ongoing fight over the drug’s health risks. While that battle has a month to go, a new study out in the British Journal of Psychiatry this backs up the idea that pot’s cognitive impairment is all about the makeup of the marijuana you’re smoking.

Valerie Curran and colleagues studied 134 volunteers as those volunteers smoked from their private stashes in their homes. The scientists had their subjects take a series of cognitive tests, both high and sober. They then took a small portion of the pot to the lab for analysis.

Curran found striking differences in the chemical compositions of different users’ marijuana, and those differences appeared to play a large role in how well the smokers performed on the tests while high.

The key difference between the types of cannabis is the ratio of two chemicals found in all strains. Tetrahydrocannabinol (THC) is the primary active ingredient, and is responsible for the effects associated with the classic ‘high’, including euphoria and giddiness but also anxiety and paranoia. The second chemical, cannabidiol, has more calming effects, and brain-imaging studies have shown that it can block the psychosis-inducing effects of THC. Skunk-type strains of cannabis contain a higher ratio of THC to cannabidiol than do hashish or herbal types. [Nature]

People who smoked marijuana with the highest cannabidiol levels—with concentrations as high as 0.75 percent—shared no impairment during the tests. But people who smoked marijuana with the lowest levels—down to 0.14 percent or less—performed worse and forgot more words while they were high. The type of pot known as skunk, which has been bred for THC potency, got the most demerits when it came to short-term memory and cognition effects.

A previous study had not found this difference — but the author of that research told Nature News that he thinks this is because his group studied only the marijuana supplied by the U.S. government, rather than the much more varied weed smoked by illegal users. [TIME]

That previous author, Aaron Ilan, says he didn’t have a choice: The government doesn’t allow U.S. researchers to study any other marijuana than what’s supplied by the National Institute on Drug Abuse. Ilan says that research weed is weak and low-quality, so the results it gives probably don’t reflect reality. The wide range of pot that the British researchers found certainly suggests the same.

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Image: Wikimedia Commons

CATEGORIZED UNDER: Health & Medicine, Mind & Brain
  • Dante The Canadian

    This is a very interesting study. The concept that certain pot may be better for us than other types, especially in terms of short term memory and speech is … ummmmm …. errrrr….

    What was I typing????

  • John Higgins

    So what they’re trying to say is indica strains of cannabis don’t give you memory loss but sativa strains do. Indicas are lower in thc and high in cbd while sativa strains are plain thc.

  • http://Untitledvanityproject.blogspot.com Rhacodactylus

    What about the long term effects? Many of the smokers I know seem to be a bit diminished overall, regardless of that days use, but this could be a case of confirmation bias on my part, or a self selection problem related to which groups choose to partake more regularly.

    Cognitive test are extremely sensitive to placebo effects, without blinding it’s tough to base too much on this study.


  • http://clubneko.net nick

    Kinda hard to double blind a pot smoking study, as anyone who smokes it will pretty immediately be able to tell the difference. Oral or intravenous administration would be needed.

    And thanks to John H above for making the point I was going to make. “Skunk” is a colloquialism to refer to potent strains, but really just means it’s pretty stinky when you smell it, which may or may not be related to potency. Sativa strains aren’t plain THC, but they do have higher concentrations of it. However, they are low-yield plants. Indica plants aren’t as “heady” (i.e. lower THC ) but are quite high yield. Most of what’s available on the street level these days are hybrids of hybrids of indica x sativa crosses, with the occasional chap experimenting with ruderalis hybrids (ruderalis provides no high in and of itself, but is an auto-florescent plant, i.e. it will flower and mature in a certain period of time irrelevant of the lighting and fertilizing conditions provided, which may be desirable qualities for headier plants).

    I mean, uhhhhh whut?

  • tom

    You were typing the munchies, Dante Dude. Dude. Dood. Doooooood.

  • JDubya

    wow. what a complete waste of 1’s and 0’s. so, what you are saying is that people are going to “vote” to have “access” to “medical” pot. fabulous. and most of these people have not a clue as to the political parties, who is the speaker of the house, or who the vp is for that matter.

    but, what is the key issue in california is…medical pot. and discover magazine puts this article out?

    how about “which video game series is more fun when you are stoned: atari 2600 or supernintendo super mario brothers?”
    “quisp or captain crunch?”

    yay, for this is the beginning of the end, america.

  • Jillian Galloway

    We must not legalize marijuana! Even if it would eliminate more than 60% of cartel revenue and end their incentive and ability to continue murdering countless innocent people. We MUST keep arresting 850,000 people a year for marijuana offenses even though, after FORTY YEARS of prohibition, marijuana use went *up* 8% last year and 6,000 people a day start smoking marijuana for the first time. We taxpayers WILL continue to pay $40 BILLION a year for the prohibition because it’s so good for us that we don’t care that it doesn’t stop people smoking marijuana and it draws drug dealers into our communities to meet the demand. The prohibition MUST last FOREVER!!!

  • Buzzby

    I knew there was a reason I prefer Sativas to Indicas! Sativas are the pure THC experience while Indicas have the CBD brakes on. Experienced users enjoy the short-term memory loss. It keeps them “in the moment”.

  • Mike

    I’d rather ask Carl Sagan his thoughts on this but…

    Most of the weed now is hybridized sativa/indica, even “skunk” types. Even some of the strongest, such as “kush” aso have varying degrees of hybridization, and are not stable genetically, as can be seen when some illegal growers grow out seeds of so-called “true breeding” strains.

    I have been to a rather famous-owned clinic where the difference in the names and prices of the weed were just buds of differing quality from the same plants and supplier. Despite the identical chemotype, some “experienced” users claimed to be able to tell a difference…

  • scott

    I am all in support of making it legal and people can smoke it all they want, I don’t care, smoke yourself into a coma if you like…but I know a lot of people who smoke it and they are all over weight, (some very obese) lethargic and all the guys have boobs* (isnt the pot estrogenic?? Can someone give me some biochem on it?). I would hold off on the stuff unless there was a medical need and find other ways to cope with stress and a needed escape from reality.
    * I just spent 5 weeks in south of France and as expected, there were many topless women on the beaches. Now, it is illegal in most of the US, yet I see obese men all over the beaches here (in LA where I live and on the Texas coast where I often go) sporting breasts often larger than most womens…so why is that not illegal? It’s a fatty, fleshy breast..with a nipple.. and usually covered in hair..so, one that makes milk is illegal and one that just sprouts hair is not? I am confused by our conservative laws banning women from going topless yet allowing an ever growing obese population of men to swing theirs around..

  • Brian Too

    To answer the article’s titular question, the strain of marijuana that puts the least strain on memory is the one made out of parsley.

    No pain no gain!

  • daniel carter

    Autoflowering Kush. Autoflower varieties tend to have more CBD; Kush also.

  • Angel420



  • http://www.coroflot.com/BlueRSX Jerry D. Elmore

    Additionally, the NIH (National Institute of Health), concedes that the cannabinoids present in marijuana have “remarkably low toxicity and that lethal doses in humans are not known” (see Potency of Tetrahydrocannabinol ):


    Yet, marijuana is illegal because according to the DEA it has a high potential for abuse, there is no medical accepted use for treatment, AND there is a lack of accepted use under medical supervision.


    Marinol, an exact chemical artificial copy of THC can be administered legally. In God We Trust does NOT apply to His marijuana.

    The threat of marijuana is not to society but to industries like paper, petroleum refineries, and drug companies.

    Consider that hemp and marijuana have renewable properties greater than trees, can be used to make plastic which make up 10% of most automobiles (http://www.ford.com/about-ford/news-announcements/press-releases/press-releases-detail/pr-ford-researchers-look-to-mother-31009), and yields twice as much ethanol as corn per acre (http://en.wikipedia.org/wiki/Table_of_biofuel_crop_yields)

    If people could grow their drugs for ailments treated by OTC drugs, the FDA would lose BILLIONS of dollars in revenue.

    It’s a wonder that it’s remained illegal for this long.

    Fortunately, or unfortunately for those industries affected, the truth shall set it free. The laws against hemp and marijuana have outlived the people who created it…but those same laws have not withstood the test of time and logic.

    Here’s hoping that legal marijuana will help us forget the pain and suffering the US government has caused millions of Americans over a non-lethal plant and lead us on the unbeaten path of renewable and sustainable practices.

  • Voice of Reason

    I think its important to point out what ‘short term memory’ really is. The layman interprets that to mean anything from minutes, to hours, to days, as fits their point of view.

    The duration of short-term memory in the order of seconds.


    The effect they’re talking about is exactly ‘…dude, what was I talking about?’, which only occurs while under the influence.

  • http://yeson19.com/index.php/pages/initiative/ EndtheDrugWar

    JDubya: Pay attention. This article has nothing to do with medical marijuana. It mentions Proposition 19, which is about legalizing cannabis in general for adults over 21. No need to consult with a doctor or anything ridiculous like that. Should Prop. 19 pass, if an adult wants to partake, they just need to show I.D. to prove they are 21+ and go to a licensed dispensary, like going to a liquor store. No more having to find a seedy dealer, risk imprisonment, fines, violence, etc. because of dealing with a black market. You care about kids? Good, then you’ll agree marijuana prohibition puts them in more danger than just regulating and taxing marijuana for adults in the same way tobacco and alcohol are.

    Don’t like marijuana? Don’t use it! Very simple. I don’t like alcohol, I have seen it destroy too many people’s lives, so I rarely ever use it (I have maybe 1-3 drinks/year, total, and could go the rest of my life without another drink and be totally o.k. with that). Tobacco killed my grandmother. I have no use for it either. Never for one second would I think it a good idea for either one of these dangerous, destructive substances to be illegal. Prohibition does not work. In case it wasn’t obvious, that is the whole point of Proposition 19, to help do away with the horrifically harmful prohibition that is far more dangerous to society than the substance known as cannabis.

    YES on Prop. 19.

  • SomethingToPonder

    My only problem with legalizing pot relates to testing for it under proper circumstances. Does anyone like the idea of abolishing a legal blood alcohol limit? Does anyone think that it’s a good idea to drive while stoned? Should you be able to operate heavy machinery, or work in high-risk areas while stoned? How do police administer a low-cost, NON-invasive test to see if you were stoned (above whatever legal limit is decided on) while driving?

    Unless we get a reasonably effective ‘stone-test’ that can be quickly administered, I have to weigh in on the side of keeping pot illegal, until the other issues of safety can be addressed.

  • d.dyke

    re; ” effective stone test ”

    Right on .Maybe all those advocates should work the streets for a while and do the cleanup and see the real effects or work in a factory where people are stoned all the time .Prohibition didn t work ,that was a long time ago and we are still trying to control the alcohol and we still haven’ t learnt how to do it .So lets compound it by adding pot and the rest of the drugs.
    Some countries have already tried this and all we have to do is look at some of the countries that produce and see their state of affairs .And what about the other chemicals in pot that stay in your system up to six months,are they okay ?

  • http://smokeweedeconomist.com smoked out economist

    what a bad test

    how do they control for one participant being just plain smarter than the other?

    maybe the guys with the strong weed were smarter…. thusly they got better scores (and bought the better weed lol!)


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