Sunday, October 3, 2010

Marijuana and Memory


Do certain strains make you more forgetful?

Cannabis snobs have been known to argue endlessly about the quality of the highs produced by their favorite varietals: Northern Lights, Hawaiian Haze, White Widow, etc. Among dedicated potheads, debates about the effects of specific cannabis strains are often overheated, and, ultimately, kind of boring. It's a bit like listening to a discussion of whether the wine in question evinces a woody aftertaste or is, instead, redolent of elderberries. For most people, the true essence of wine drinking is pretty straightforward: a drug buzz, produced by a 12 to 15 % concentration of ethyl alcohol derived from grapes, which can be had in a spectrum of varietal flavors.

However, there is no doubting that, unlike the case of wine, different strains of marijuana can have markedly different psychoactive effects. With weed, it's not just a matter of taste.

Over the past couple of years, the cannabis debate has taken a nasty turn, after British scientists published several controversial studies suggesting that high-THC "skunk" cannabis was responsible for increased mental problems among young people--including an increased risk of developing the symptoms of schizophrenia. British drug policy makers have continued to lead the charge on this, with mixed results. See my earlier post.

Recently, a study published in the British Journal Of Psychiatry concluded that marijuanaThis post was chosen as an Editor's Selection for ResearchBlogging.org
high in THC--including so-called "skunk" cannabis--caused markedly more memory impairment than varieties of marijuana containing less THC.

In an article at Nature News, Arran Frood spelled out the details of the study:

"Curran and her colleagues traveled to the homes of 134 volunteers, where the subjects got high on their own supply before completing a battery of psychological tests designed to measure anxiety, memory recall and other factors such as verbal fluency when both sober and stoned. The researchers then took a portion of the stash back to the laboratory to test how much THC and cannabidiol it contained....  Analysis showed that participants who had smoked cannabis low in cannabidiol were significantly worse at recalling text than they were when not intoxicated. Those who smoked cannabis high in cannabidiol showed no such impairment."

The two main ingredients in cannabis are THC and cannabidiol (CBD). CBD shows less affinity for the two main types of cannabis receptors, CB1 and CB2, meaning that it attaches to receptors more weakly, and activates them less robustly, than THC.  The euphoric effects of marijuana are generally attributed to THC content, not CBD content. In fact, there appears to be an inverse ratio at work. According to a paper in Neuropsychopharmacology, "Delta-9-THC and CBD can have opposite effects on regional brain function, which may underlie their different symptomatic and behavioral effects, and CBD's ability to block the psychotogenic effects of delta-9-THC."

So, CBD specifically does not produce the usual marijuana high with accompanying euphoria and forgetfulness and munchies. What the researchers found was that pot smokers suffering memory impairment and those showing normal memory "did not differ in the THC content of the cannabis they smoked. Unlike the marked impairment in prose recall of individuals who smoked cannabis low in cannabidiol, participants smoking cannabis high in cannabidiol showed no memory impairment."

As far as memory goes, THC content didn't seem to matter. It was the percentage of CBD that controlled the degree of memory impairment, the authors concluded. "The antagonistic effects of cannabidiol at the CB1 receptor are probably responsible for its profile in smoked cannabis, attenuating the memory-impairing effects of THC. In terms of harm reduction, users should be made aware of the higher risk of memory impairment associated with smoking low-cannabidiol strains of cannabis like 'skunk' and encouraged to use strains containing higher levels of cannabidiol."

The idea that cannabidiol may protect against THC-induced memory loss is still quite speculative.  Other research has suggested that a paucity of CB1 receptors may be protective against memory impairment. Marijuana growers select for high-THC strains, not high-CBD strains, and thus there is little data available about the CBD levels of most marijuana.

An earlier study in Behavioural Pharmacology by Aaron Ilan and others at the San Francisco Brain Research Institute did not find any connection between memory and CBD content. However, Ilan speculated in the Nature News article that the difference might have been due to methodology: In Britain, the subjects were studied using marijuana of their own choosing.  In the U.S., National Institute of Health research policy has decreed that marijuana for official research must be supplied by the National Institute on Drug Abuse (NIDA). And if there is one thing many researchers seem to agree on, it is that NIDA weed "is notorious for being low in THC and poor quality."

But CBD still does something, and that something just might be pain relief.  Lester Grinspoon, a long-time marijuana researcher at Harvard Medical School, thinks that if the study proves out, it could have an important impact on the medical use of marijuana. Also quoted in Nature News, Grinspoon said: "Cannabis with high cannabidiol levels will make a more appealing option for anti-pain, anti-anxiety and anti-spasm treatments, because they can be delivered without causing disconcerting euphoria."


Morgan, C., Schafer, G., Freeman, T., & Curran, H. (2010). Impact of cannabidiol on the acute memory and psychotomimetic effects of smoked cannabis: naturalistic study The British Journal of Psychiatry, 197 (4), 285-290 DOI: 10.1192/bjp.bp.110.077503

Graphics Credit: http://sites.google.com

16 comments:

Adi Jaffe said...

I have to say I LOVE the researchers' suggestion that individuals specifically select marijuana strains low in THC - they've obviously NEVER talked to a weed smoker...
I'm almost laughing out loud in my office (yes I'm in my office on sunday, so what?!)

Dirk Hanson said...

Yes, best of luck selling the weed with the crummy buzz. Good for your hippocampal health probably not a viable sales strategy.

Anonymous said...

Sounds like the researchers could be smoking as much as the people they studied. Memory can be very selective.

Neuroskeptic said...

"Marijuana growers select for high-THC strains, not high-CBD strains"

It would be interesting to check this, though. Maybe people do select for CBD content, not chemically, but on the basis that the subjective effects are different.

Steve Clay said...

Then it makes sense that Sativex chose a nearly a 1 to 1 ratio of CBD to THC.

If (in an alternate universe) weed were regulated to have nearly the same amount of CBD, couldn't the user simply increase dosage to get a desired intoxication? I.e. as I understood it CBD mitigates, but does not eliminate, the euphoria.

Dirk Hanson said...

Quite possibly pot smokers do (unconsciously) select for their preferred ratio of THC/CBD. That would make an interesting study.

Lee @ AddictionBlog.org said...

NIDA grows weed? Where? And in terms of tweaking ratio ... I would think most pot smokers actually have no idea what THC or CBD are. As a former consumer myself, I gave little attention to the chemistry of the whole operation. And darn it, my memory HAS been affected. I think...

Neuroskeptic said...

True, but smokers are always comparing strains - this one is mellow, this one is sleepy, this one is hallucinogenic, etc.

This might just refer to the THC content (or even to other drugs unscrupulously added to the stuff), but it might also refer to the other cannabinoids.

Anonymous said...

"Adi Jaffe said...

I have to say I LOVE the researchers' suggestion that individuals specifically select marijuana strains low in THC - they've obviously NEVER talked to a weed smoker..."

No they said GROWERS select for high THC, which they do, especially in the black market as opposed what you could call the green market for pot. Just look at the average stuff on the street, it's mostly high THC, it's a very important point!

It's a great reason for legalization because we could ensure we know what we are smoking etc...

lisafurr said...

That is why cannabis is medicinal. Different strains for different ailments. I have had MS for 20 years. A joint might not help a newt, but it does wonders in my bed ;-)

MAT said...

The central problem with this study is that the CBD enriched strains are rare. Vanishingly so in the US (going by seizure data, we sorely need an update in the era of boutique medical MJ) and a minority of their sample in this paper.

Question is, who is getting these strains? Are they self-selecting in any way? If so, that blows random assignment...and therefore any confidence whatsoever about pre-existing differences in cognitive performance.

MageYouLook said...

personally i find that sativa in small amounts increases my ability to concentrate and remember.

i developed both sativa and indica pills. the sativas are good for the day. being edible and having made them very low doses they act like a light stimulant. i would describe the effects of being in love and super motivated.

experimenting with indica pills even in very light doses i have noticed has more of an effect on memory deficits. (indica has a higher CBD as medical grade is meant for pain relief and such over euphoria)

as reported it sounds like CBD is a big factor in memory issues.

So i would say strain only matters as far as they have described in terms of the ratio and strength of the THC to CBD.

Anonymous said...

This is quite deceptive. The original study was on people who smoked pot HIGH in CBD, not LOW in THC!

Anonymous said...

One large factor not mentioned here is that there are 66 Cannabinoids in cannabis, THC & CBD are only 2 of those.
As more and more studies are looking into more of the Cannabinoids and finding out more on them, varying effects etc it seems obvious to me that they are major contributors to how they make you feel (THC & CBD aside).

Anonymous said...

They said high in thc low in cbd. Quit smokin soo much. Nobody picks high cbd because the consumers want to get "fucked up" instead of properly medicated. I have yet to find a grower who grows a high cbd strain which is shown to have the best medical benefits. Not sure where the logic is there considering they are growing for patients..

Anonymous said...

This i would believe! Some people naturally like a northern lights more than a skunk (just an example) and it could easily be due to cbd content

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