The research that is the subject of this article[1] made the rounds a few months ago in the anti-cannabis movement. Here are some excerpts worth repeating:

"Marijuana participants were not excluded if they had used other illegal drugs in the past"

Also, in the 2nd to last paragraph (emphasis mine):

"This preliminary study has several caveats. First, the sample size does not provide power to examine complex interactions such as sex differences. Because this is a cross-sectional study, causation cannot be determined, although marijuana exposure parametrically correlated with structural differences, which suggests the possibility of causation. Longitudinal studies are needed to determine whether marijuana exposure explicitly leads to the differences observed in this study."

Checking out some of the players where the research money came from (National Institute on Drug Abuse, the Office of National Drug Control Policy, Counterdrug Technology Assessment Center), it is no wonder the various news articles and the paper itself tried so hard to illustrate some causation. They ended up with a handful of people and some correlative results.

[1] - http://jn.sfn.org/press/April-16-2014-Issue/zns01614005529.p...

One of the problems with the illegality of cannabis is that research is terrible because of the laws.

I strongly favour legalisation of all drugs. This would allow much better research.

Having said that the knee-jerk denialism that cannabis could possibly cause any harm at all is weird to see on HN.

Playing Super Mario is also associated with brain changes [1]. Perhaps the answer is simply that as humans, our brains change quite a lot in response to our habits, and that such changes are unremarkable.

1. http://www.nature.com/mp/journal/v19/n2/full/mp2013120a.html

I'm naive here, but won't some brain changes have to happen when becoming addicted to nicotine when smoking cigarettes?

Would it be safe to say that, any drug that alters your state of mind will cause a brain change? (Legal or illegal)

It's amazing to me that medical journals print results based on 20 control and 20 test subjects.

I remember sitting at a table with some neuroscientists in Berlin, and it turned out that they all smoked from time to time. They were really casual about it. Sure, marijuana is bad but alcohol is worse and we all do that.

This study presents an extraordinary claim but, if the comments mentioning of 20 subjects are correct, does not present extraordinary evidence.

|In the current study, Jodi Gilman, PhD, Anne Blood, PhD, and Hans Breiter, MD, of Northwestern University and Massachusetts General Hospital/Harvard Medical School used magnetic resonance imaging (MRI) to compare the brains of 18- to 25-year olds who reported smoking marijuana at least once per week with those with little to no history of marijuana use.

Most people who consume marijuana regularly would not admit that information. This is not and cannot be a representative sample. Also correlation causation problems and tiny (20 people) sample size.

The biggest problem with this study is a huge selection effect. The users of marijuana are very different then non users, and heavy users are very different from light light users. This by itself would show large correlations across a large swath of measurements.

Anybody over 50 here that uses marijuana regularly and is still sharp?

That's an honest question, my own connections do not include programmers over 50 that smoke marijuana regularly so I'm curious how many people would bill themselves as such.

Are brain changes an inherently bad thing?

btw, didn't the US pass a law to defund research on marijuana?

tl;dr: "The scientists found that the more the marijuana users reported consuming, the greater the abnormalities in the nucleus accumbens and amygdala. The shape and density of both of these regions also differed between marijuana users and non-users."

Nucleus accumbens: responsible for pleasure & reinforcement, maternal behavior. Direct stimulation has been shown to successfully decrease the effects of depression.

Amygdala: Responsible for emotional learning, memories of emotional experiences, memory consolidation, and emotional regulation.

All sources Wikipedia. I am not a neuroscientist, just trying to get a better understanding.

"was larger and altered in its shape" that makes sense because when i'm high i can feel much more emotion... with small animals.