Social Question

deni's avatar

So does smoking weed kill your brain cells or not?

Asked by deni (22607points) February 29th, 2012

You hear it does in one study, then you hear it doesn’t in another. So is there an unbiased study we can look at? DOES IT OR DOESN’T IT? It seems simple enough. I’m sure it’s more complex but maybe someone could explain it to me a little better? Is it that smoking weed does kill brain cells, but we have SO MANY BRAIN CELLS and we use a small percentage of them that it usually isn’t killing off any crucial brain cells? Oh god I have no idea, anybody know? Anything? huhh? huh?

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22 Answers

Aethelflaed's avatar

From NORML (so, not in any way an unbiased source, but a good starting place?)

Myth: Pot Kills Brain Cells

Government experts now admit that pot doesn’t kill brain cells.1 This myth came from a handful of animal experiments in which structural changes (not actual cell death, as is often alleged) were observed in brain cells of animals exposed to high doses of pot. Many critics still cite the notorious monkey studies of Dr. Robert G. Heath, which purported to find brain damage in three monkeys that had been heavily dosed with cannabis.2 This work was never replicated and has since been discredited by a pair of better controlled, much larger monkey studies, one by Dr. William Slikker of the National Center for Toxicological Research3 and the other by Charles Rebert and Gordon Pryor of SRI International.4 Neither found any evidence of physical alteration in the brains of monkeys exposed to daily doses of pot for up to a year. Human studies of heavy users in Jamaica and Costa Rica found no evidence of abnormalities in brain physiology.5 Even though there is no evidence that pot causes permanent brain damage, users should be aware that persistent deficits in short-term memory have been noted in chronic, heavy marijuana smokers after 6 to 12 weeks of abstinence.6 It is worth noting that other drugs, including alcohol, are known to cause brain damage.


1. Dr. Christine Hartel, Acting Director of Research, National Institute of Drug Abuse, cited by the State of Hawaii Dept of Health, Alcohol and Drug Abuse Division in memo of Feb. 4, 1994.

2. For an overview, see NATIONAL ACADEMY OF SCIENCES Report, op. cit., pp. 81–2. R.G. Heath et al, “Cannabis sativa: effects on brain function and ultrastructure in Rhesus monkeys,” Biol. Psychiatry 15: 657–90 (1980).

3. William Slikker et al., “Chronic Marijuana Smoke Exposure in the Rhesus Monkey,” Fundamental and Applied Toxicology 17: 321–32 (1991).

4. Charles Rebert & Gordon Pryor – “Chronic Inhalation of Marijuana Smoke and Brain Electrophysiology of Rhesus Monkeys,” International Journal of Psychophysiology V 14, p.144, 1993.


6. “Cannabis and Memory Loss,” (editorial) British Journal of Addiction 86: 249–52 (1991)

Pandora's avatar

Good question. Interesting that alcohol is allowed and does long term physical damage and yet marijuana isn’t. I suppose the real concern is not being able to tell the coke users from the pot users.

Michael_Huntington's avatar

But listening to state sponsored propaganda does.
Anti-drug ads are fucking hilarious

JLeslie's avatar

Even if it doesn’t, which it seems it doesn’t, people I know who use pot regularly, daily, are users. Abusers. Addicted. They don’t believe they are addicted, but to me they are, they act like addicts, and I think any professional who treats addicts would agree. So, MJ does not have some sort of free pass in my opinion. I realize that is not exactly your question though. Looks like @Aethelflaed gave a great reference.

captainsmooth's avatar
I have smoked pretty much daily since 1991, have a graduate degree, work a full time job and a couple of part time jobs equaling about 55 hours a week. I have two children that I have half custody of, get them to school fed, dressed, homework done, attend all their school functions, conferences, etc. I coach their teams. I also mountain bike, exercises pretty regularly.

If I didn’t tell you I was high, you would never know.

So I am going with no, smoking weed does not kill your brain cells.

JLeslie's avatar

@captainsmooth Congratulations, you are a well functioning pot smoker. I also personally know two people who are like you. They also are not fun to be around when they don’t get their toke. One of them had a bad anger problem, but of course that can happen even without the smoking. I say gice stopping a try, and see how badly and fast you want to go back to it, and if your loved ones see a difference in your personality. Maybe you can smoke every day for the rest of your life, but I still say you are most likely addicted. But, hey, caffiene drinkers are addicted; addicts. They get withdrawal symptoms, the drug is mood altering for most, it causes physiological changes, but no one is outlawing caffeine.

deni's avatar

@JLeslie I just don’t think its extreme enough to need to be worried about for most people. I only know one person who is like you mentioned….angry when they don’t get their weed. But you know what, he is angry to begin with! Even when he’s high! I completely agree with you that it is an addiction. But I believe it’s psychological and I don’t really think usually it’s a big deal. Here’s how I get over it when I don’t have any pot: “Aw, dammit. Wish I had some.”....then I go on with my day.

@captainsmooth You’re one of the lucky ones! I am not a functioning high person. I’m great to talk to, but fumble-y if I’m trying to work or get something done.

And I asked this question because I know being a daily user for the past couple years has made me forgetful. I used to have the sharpest memory and now I run to the back at work and forget what I went for, almost every single time. And I’m wondering about why that is. I’ll admit I think its an issue, for me, but I still feel 99.9% this way regarding the fact that its still illegal while people can just gorge themselves on alcohol on a daily basis.

JLeslie's avatar

@deni Well, you can see by my answer that I compared it to caffeine, so it is not that I think pot is all evil. However, I do think it is more of an issue than most regular smokers think or want to believe. Just my opinion. I think this about people who drink every day also, even if it is just wine or beer.

nikipedia's avatar

Are you actually interested in whether it reduces the number of brain cells, or are you asking in general about whether it has negative effects on your cognitive functioning?

deni's avatar

I know that it has negative effects, I was also curious about the studies regarding it killing your brain cells or not, but I’m sure that’s only one aspect of it.

nikipedia's avatar

I ask because cell death isn’t necessarily associated with decreases in cognitive function. (Adult brains have far fewer neurons than infants, and you go through at least two stages of massive brain cell death in your life that are associated with normal development.)

That said, THC is associated with brain cell death: Here we report that Δ9-tetrahydrocannabinol (THC), the major psychoactive component of marijuana, is toxic for hippocampal neurons.

It is also associated with changes to the shape of brain cells: Electron micrographs revealed a striking ultrastructural appearance and statistically significant decreases in mean volume of neurons and their nuclei sampled from the hippocampal CA3 region of rats treated with the highest doses of THC. A 44% reduction in the number of synapses per unit volume was demonstrated in these same rats. Golgi impregnation studies of additional groups of rats treated with 10 or 20 mg/kg/day THC and sacrificed 2 months after their last treatment with THC revealed a reduction in the dendritic length of CA3 pyramidal neurons, despite normal appearing ultrastructure and no changes in synaptic density. (Electron micrographs are pictures of cells, hippocampal CA3 regions are brain regions that are critical for learning and memory, and Golgi impregnation is a way of staining cells so you can look at their shape.)

I have been in the brain business for a while now. I think to answer your question, it is less interesting to look at what happens to cells, and more interesting to look at what happens to behavior. I can get some studies on that for you too if you’re interested.

sadconfusion's avatar

It doesn’t kill brain cells, but it can cause chemical reactions in the brain if you smoke it regularly. And can lead to Mental health disorders such as Schizophrenia, which doesn’t happen to everyone.

deni's avatar

@nikipedia I would be interested in seeing those, thanks!

Earthgirl's avatar

I know this doesn’t answer your question, sorry, but I was going to say that it’s carcinogenic. It does have carcinogenic components but it seems that so far, they have not been able to prove an appreciable increase in risk of cancer from smoking pot. Anyone with conflicting evidence please chime in! I really thought it did and though I don’t smoke now, I did in the past. I had heard that the amount of carcinogens in cannabis was 10X higher than cigarettes. Then I read that although that may be true the average pot smoker smokes way less than a cigarette smoker so the effect is negligible. Seems like the jury is still out but so far the cancer risk seems low. As I said, correct me if I am wrong. I am a cancer survivor and I like knowing the truth.

likipie's avatar

Of course it does. Is that going to stop us from doing it? Obviously not.

deni's avatar

@likipie Definitely not especially judging by your avatar hahaha!

MollyMcGuire's avatar

Interesting article:

“Marijuana smoke contains carcinogens and a higher level of tar compared to cigarettes and users are at much greater risk of developing lung cancer. Marijuana also has negative effects on the reproductive system; reducing testicular size, lowering testosterone levels, decreasing libido, causing menstrual abnormalities, abnormal ova formation, impotence and changes in sperm shape and motility.”

Aethelflaed's avatar

@MollyMcGuire I don’t know that the Daily Buggle is a reputable source, when the OP was asking for scholarly studies.

MollyMcGuire's avatar

@Aethelflaed I don’t know either. I just found it. The author claims to be an M.D. but there are plenty of nutbags running around with a medical degree. I just said it was an “interesting” article, which I thought it to be.

Earthgirl's avatar

this article cites a few scientific studies showing no or low cancer risk from marijuana and says they have been discredited. He believes that even medical marijuana should never be smoked.

mattbrowne's avatar

It changes brain chemistry. Like all psychoactive substances.

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