Adolescent-onset Persistent Cannabis Users Show Permanent Neuropsychological Decline

[PC LOAD LETTER]

http://www.pnas.org/content/early/2012/08/22/1206820109.abstract


Recent reports show that fewer adolescents believe that regular cannabis use is harmful to health. Concomitantly, adolescents are initiating cannabis use at younger ages, and more adolescents are using cannabis on a daily basis. The purpose of the present study was to test the association between persistent cannabis use and neuropsychological decline and determine whether decline is concentrated among adolescent-onset cannabis users. Participants were members of the Dunedin Study, a prospective study of a birth cohort of 1,037 individuals followed from birth (1972/1973) to age 38 y. Cannabis use was ascertained in interviews at ages 18, 21, 26, 32, and 38 y. Neuropsychological testing was conducted at age 13 y, before initiation of cannabis use, and again at age 38 y, after a pattern of persistent cannabis use had developed. Persistent cannabis use was associated with neuropsychological decline broadly across domains of functioning, even after controlling for years of education. Informants also reported noticing more cognitive problems for persistent cannabis users. Impairment was concentrated among adolescent-onset cannabis users, with more persistent use associated with greater decline. Further, cessation of cannabis use did not fully restore neuropsychological functioning among adolescent-onset cannabis users. Findings are suggestive of a neurotoxic effect of cannabis on the adolescent brain and highlight the importance of prevention and policy efforts targeting adolescents. HOWEVER. Notice in the last few sentences of the abstract:

"Impairment was concentrated among adolescent-onset cannabis users ..."

To date, there has not been any observed neurotoxic effects on the adult brain. This simply means, developing brains should not use drugs. This should have already been "common sense", as there are similar effects with alcohol (albeit unlike cannabis, neurotoxicity with alcohol doesn't go away when your brain stops developing).

This is simply data that implies that there should be a minimum age before you can safely smoke weed. Say, 21 (or whenever the brain's done doing its thing).

Full PDF if anyone's interested: http://www.rjbf.com/PNAS_Meier.pdf

Also, remember this is just one study. Things will get really interesting when this study is duplicated, if the results are confirmed. To date, there has been no other study to my knowledge that has shown neurotoxic effects in relation to cannabis use. Only more research will tell.

[Silvr]

Nevermind, I misunderstood part of your comment.,.

[leftistman]

It's common sense that there are harmful effects of frequent drug use.

[PC LOAD LETTER]

It's common sense that there are harmful effects of frequent drug use.
Perhaps you shouldn't pay so much attention to DARE. You can't lump all psychoactive chemicals into one category of "harmful drugs". You're being intellectually dishonest.

I don't want this to turn into another debate thread Re: drugs, but up until now no legitimate study has ever shown cannabis to be neurotoxic. There is no brain damage and there are no permanent effects on the body. For an adult user, according to this study. This study has simply observed cognitive dysfunction in adolescents only. And what's more, this is a single study. The way science works, it will be duplicated and reviewed. Then we can draw a conclusion. There is a chance they did not control for another variable and further studies may reveal this study to be flawed.

So please, GTFO with your D.A.R.E. talking points.

[cynicles]

It's common sense that there are harmful effects of frequent drug use.
lol

"Socialism can't work because the government can't just keep spending other people's money, it's common sense!"

"Global warming shouldn't be causing cold winters, it's just common sense!"

[leftistman]

Perhaps you shouldn't pay so much attention to DARE. You can't lump all psychoactive chemicals into one category of "harmful drugs". You're being intellectually dishonest.

I don't want this to turn into another debate thread Re: drugs, but up until now no legitimate study has ever shown cannabis to be neurotoxic. There is no brain damage and there are no permanent effects on the body. For an adult user, according to this study. This study has simply observed cognitive dysfunction in adolescents only. And what's more, this is a single study. The way science works, it will be duplicated and reviewed. Then we can draw a conclusion. There is a chance they did not control for another variable and further studies may reveal this study to be flawed.

So please, GTFO with your D.A.R.E. talking points.
I didn't say that all drugs are completely harmful in even the most moderate dosage, what I meant is that even something like weed which is not particularly harmful can become very unhealthy if used frequently. You ignored my use of the word "frequent." I'm not a radically anti-marijuana legalization conservative, I'm someone who accepts that frequent use of the drug can cause respiratory problems, reproductive problems, and an increased risk of testicular cancer. I do realize that most users will not be permanently affected by weed.

[Positivist]

This is problematic because the brain never stops developing. That being said, there is a period of time when neural development proceeds to occur significantly slower. Though again at what age this occurs varies according to different genetic sequencings and different levels of education.

[L.A.P.]

I'm very skeptical of this, it comes off as just politically motivated anti-drug crap

[cynicles]

The thing is, these studies will always be viewed with extreme suspicion given the liberal use of deception and lying that was and has been prevalent around the issue of marijuana.

[Raúl Duke]

good thing I started at like 19, and I'm not a frequent user.

[Silvr]

I enjoy smoking and have been doing it since I was about thirteen. I think it is stupid though when people have this knee jerk urge to deny any evidence that weed can have any potential negative effects, just because they like doing it. I don't think there is anything fishy about this study.

[Skyhilist]

Doesn't even really mean that smoking marijuana as a minor is harmful in most instances. I mean once or twice I week is pretty much harmless, even for an adolescent. It basically just means that perhaps you shouldn't smoke weed "erryday" as a minor.

[Jazzratt]

Similar findings exist regarding alcohol and I'd be rather unsurprised to find that other recreational drugs cause similar problems in the same circumstances (that, in fact may be an interesting thing to look into). It seems that repeated excitement and/or inhibition of given receptors in a developing brain can inhibit normal brain development - which suggests worrying things about the effects of certain therapeutic drugs (especially those used in the treatment of psychiatric problems) which probably requires more investigation.

[ZvP]

Most kids who use marijuana *habitually* THAT early probably don't care about anything anyway and have let their brains rot away. There are so many factors that it's impossible to conclusively determine marijuana was the culprit.

[Silvr]

Most kids who use marijuana *habitually* THAT early probably don't care about anything anyway and have let their brains rot away.

That seems like a pretty baseless assumption.

[cynicles]

It would be nice to see some other factors accounted for, especially social ones.

[MarxSchmarx]

One slight of hand those defending cannabis often invoke is that they compare the effects of cannabis to alcohol/tobacco. Although I think the epidemiology of cannabis and alcohol (and maybe tobacco) are just too different to be able to draw many usefully conclusions, it is true that alcohol/tobacco are probably objectively among the worst drugs out there. Thus, it's not terribly surprising that alcohol/tobacco are far worse. True, the governments are hypocritical about controlling cannabis the way they do, but that doesn't mean it's harmless or that we should even remotely expect it to be so.

[Jazzratt]

Most kids who use marijuana *habitually* THAT early probably don't care about anything anyway and have let their brains rot away. I don't think that neuropsychological decline has ever been linked to apathy in the same way. Simply not caring doesn't have the same adverse physical effects ("rotting" the brain*).


There are so many factors that it's impossible to conclusively determine marijuana was the culprit.
I'm not so sure. Similar agents have been shown to have similar effects it would be incredibly odd if cannabis were that different. This is one study but it does seem to suggest that cannabis (the primary common factor in those studied) is at least partially responsible.

Incidentally I think that people who want to pretend that cannabis is completely harmless, especially as part of an argument that it should be legal, are doing themselves a disservice. I like smoking weed, I don't do it nearly enough for a whole bunch of reasons none of which concern my health, but I know that I'm doing it for fun not because it's a totally healthy thing to do.

*Incidentally I'm not a big fan of saying anything rots the brain. The phrase is unpleasant and largely an inaccurate assessment of what is occuring.

[ÑóẊîöʼn]

Looking in the study for specific confounding variables:

1) Tobacco mix or pure (if smoked). The study claims to rule out "persistent tobacco dependence" as an alternative explanation for impairment, but does not clarify whether that means that smoked cannabis was mixed with tobacco or not.

2) Smoked, vapourised, eaten or drank. No mention is made of how the subjects consumed their cannabis.

3) Indica or Sativa. No mention made.

4) Strain of cannabis and the various different cannabinoids in each strain. No mention made.

5) Quality and strength of cannabis. Mention is made on page 6 that "the potency of cannabis obtained from police seizures in New Zealand is similar to that of cannabis in the United States". However in the US, and therefore presumably therefore in NZ as well, cannabis is available in multiple qualities and strengths.

6) Possible contamination of cannabis e.g. gritweed, soap bar hash. No mention made.

7) On education:


Alternatively, persistent cannabis users may experience greater neuropsychological decline relative to nonusers because they receive less education. Our results suggest that cannabis-associated neuropsychological decline does not occur solely for this reason, because the association between persistent cannabis use and neuropsychological decline was still apparent after controlling for years of education. Notably, the aforementioned processes are not mutually exclusive and may, in fact, be interrelated. For example, the toxic effects of cannabis on the brain may result in impaired neuropsychological functioning, poor academic performance, and subsequent school dropout, which then results in further neuropsychological decline. In this case, our statistical control for education in the analysis of the association between persistent cannabis use and neuropsychological decline is likely an overcontrol (36).

8)The scope of the study is limited. On page 6: "...these findings are limited to a cohort of individuals born in Dunedin, New Zealand in the 1970s."

Of course, if cannabis was legal to possess then we could actually carry out proper studies of its human health impact.

[Jazzratt]

Looking in the study for specific confounding variables:

1) Tobacco mix or pure (if smoked). The study claims to rule out "persistent tobacco dependence" as an alternative explanation for impairment, but does not clarify whether that means that smoked cannabis was mixed with tobacco or not.

2) Smoked, vapourised, eaten or drank. No mention is made of how the subjects consumed their cannabis. If one were to redesign this study to truly rule out tobacco use then it would be necessary to be fairly sure that the cannabis was consumed by eating, vapourising or drinking it. I doubt this was done here, however I'm not sure there is any existing evidence of neuropsychological decline in tobacco users.


3) Indica or Sativa. No mention made.

4) Strain of cannabis and the various different cannabinoids in each strain. No mention made.

5) Quality and strength of cannabis. Mention is made on page 6 that "the potency of cannabis obtained from police seizures in New Zealand is similar to that of cannabis in the United States". However in the US, and therefore presumably therefore in NZ as well, cannabis is available in multiple qualities and strengths.

6) Possible contamination of cannabis e.g. gritweed, soap bar hash. No mention made.
I'm not sure how practical it would be for these variables to be controlled - this was a study of people who had smoked all their life since adolescence: the chance that any of them stuck to a single strain or quality is vanishingly small. Indeed since most people will smoke all sorts of shit throughout their life depending on things like financial circumstances or access then it seems more sensible to test people also subject to these conditions. It would be useful, though, to see if highly contaminated cannabis is more likely to cause these things as it is disproportionately the young and poor who smoke things like soap bar.


Of course, if cannabis was legal to possess then we could actually carry out proper studies of its human health impact.
Absolutely, of course there are some in the anti-cannabis camp that cite lack of research into possible harm as a reason to keep it illegal which is a complete fucking nonsense.

EDIT: In case it's unclear I do not take the results of this study to be absolute gospel: as has been pointed out the scope was too small and some of the confounding factors were inadequately ruled out or not considered at all. A larger number of similarly sized studies with appropriately corrected methodologies would be nice to see, though I'm not holding my breath.