NIDA for Teens: The Science Behind Drug Abuse
Find NIDA for Teens on: NIDAnews on Twitter NIDANIH on YouTube NIDANIH on Facebook
Comment permalink

Can Smoking Marijuana Actually Lower Your IQ?

You are here

By Carol Krause, Chief of NIDA’s Public Information and Liaison Branch
October 09, 2012

Many teenagers assume smoking weed is harmless because of all the myths floating around saying it’s safe. What few people know is that the age you start using marijuana actually makes a difference. In fact, if you start smoking it as a teenager, there can be some serious problems for you down the road.

Although we already knew from past research that if you start smoking pot as a teen, you’ll be more likely to get addicted, new research (just published in a well-known journal called Proceedings of the National Academy of Sciences) now says if you smoke marijuana heavily as a teenager, it can actually lower your IQ!

Scientists looked at more than 1,000 people born in 1972 and 1973. When they were 13 years old, they were given IQ and other kinds of intelligence tests. They were interviewed every few years about their use of marijuana and then tested again when they were 38 years old.

The results? Those who smoked weed heavily as teens showed mental decline even after they quit using the drug—and had, on average, an 8-point drop in their IQ scores. An 8-point loss could push a person of average intelligence into the lower third of testers. Those who started smoking pot after age 18 also showed some decline, but not as much.

This was an interesting study because it also collected information from people who knew the study participants. They reported that people who smoked marijuana heavily had more memory and attention problems and did not organize their lives as well, misplacing things and forgetting to keep appointments, pay bills, or return calls. This highlights the lasting effect marijuana can have on the teenage brain, which is still developing and still wiring itself to handle the onslaught of information it gets every day. The toxic chemicals in marijuana can mess up that wiring process and hurt your ability to do well in school and in life.

Carol Krause is the Chief of the Public Information and Liaison Branch at NIDA. Since arriving at NIDA in 2006, Ms. Krause has launched several new innovative programs for teens, including Drug Facts Chat Day (an annual live Web chat between NIDA scientists and teens), National Drug Facts Week (to stimulate community events between scientists and teens), and the first Addiction Science Awards for high school participants in the Intel International Science and Engineering Fair.

Comments

" Those who started smoking pot after age 18 also showed some decline, but not as much."

Can you post a link or citation please? I don't think this was shown in the research. Was there really a significant drop? And was it in heavy smokers or all?

Great questions! This study by Meier, et al was published in August, 2012, in the PNAS Journal. To see the paper, go to http://www.pnas.org/content/early/2012/08/22/1206820109.abstract?sid=aac.... As mentioned, the researchers found the biggest decrease in those who started smoking before age 18. In this study, the researchers did not find a decline in IQ among infrequent smokers who started smoking as adults. They did find a decline in IQ in frequent smokers who started smoking as adults. This finding was significant at 0.11 level – not usually considered statistically significant; but still “significant.”

Fascinatingly enough, most scientists will tell you that p<0.05 is the significant level, not 0.11. One IOH study of marijuana use did find with p<0.05 that users experience lower cancer rates, an actually "significant" statistic. There's little point in applying statistical methodologies if we the ignore conventially accepted thresholds for what is significant versus what is chance variation in sample population, or bias due to non-corrected for variables.
This news that marijuana helps cancer sure is not helping moms not wanting kids to try marijuana It seems to me studies can be done on just about everything and have data that may or may not be statiscal or accurate depending on who sponsers the study Have you seen the data on marijuana linked to schizphrenia There is no cure for that. They say mental health causes drug abuse....I think drugs bring on the mental health problems Kids brains are developing to age 26.... 18 is to young to make it okay to be stupid, get high and drive
You used the word "to" instead of "too". The irony

it is one of the most drug used and so many think it is not bad for you. When fact it really mess you up

Marijuana does not mess you up. The only reason there was a decline in their IQ score was because they smoked it when they were a kid when there brain is still developing. Smoking marijuana or consuming it by other methods is completely harmless. Although smoking it can leave tar in the lungs, but that cannot cause death. 0 deaths have been linked to the consumption of smoking marijuana.

We all agree that smoking marijuana can cause addiction and benefits, but we are a bit harsh when giving examples of studies that seem unscientific as that exposed on IQ.
No to drugs that's for sure.
[commercial link removed, per guidelines]

Smoking is very dangerous for the teenagers.If they do not feel the bad effect but finally they face different problems. To avoid this, the government should take a effective step.
thanks for posting such kinds of conspicuousness topic.

i have a theroy i personaly think that it is not for everyone yes,but if it truly helps you to deal with your deamons then to each their own. No one person is the same

ive smoked weed since i was 12 yrs old all through out my life daily, & have never been addicted to it & still have straight A's in all my college & school classes ! I also have NEVER done any other drugs... Its always the ppl who dont smoke it who have the most negative things to say

CONGRATULATIONS !
So did my son. Unfortunately, his story has very different end result. 14 yrs old IQ 109; 17 Yrs old IQ 88; 21 years old IQ 69- mild retardation; paranoid schizophrenia. Bleak outcome. He though he was infallable too.

no smokeing bud dous not lower your iq

No,* smoking* does* IQ.* It obviously lowered your IQ.

Marijuana is not good for health and study

[commercial link removed, per guidelines]

smoking weed is bad if you are in high school. i didn't graduate because of it. tell your kids to stay away from weed until college.

well, this was a test done inside the developmental stages of life. the frontal lobe is still developing in teenagers, and therefor, their mental development will suffer because THC targets that area of the brain. Use of marijuana does impair cognitive function while under influence, but these affects are not permanent. Even cognitive function of heavy users (five joints a week or more) returns to normal after usage stops for three days or so. I would assume that many of these test subjects still smoked upon a regular basis. The claim that marijuana "makes you stupid" is a myth. I would suggest visiting [link removed, per guidelines] for some more reliable information.

I completely agree with JRose ... i always hear people talking about how it's bad for you. i don't understand why doctors would recommend it then if it didn't help you. it comes out of the ground and that means that God created it. If you would just try it you would change your mind. it's a good stress reliever and i think if it was legal everywhere then our world would possibly go out of debt and maybe our world would actually be a better place to live in. that's just my opinion though.

The argument that something is good - or not bad - for you because it is natural or “comes out of the ground” or that “God created it” is not the best one – there are many natural things that are harmful or even deadly that come out of the ground. Also, your statement about “why doctors would recommend it if it didn’t help you” makes many assumptions, which may or may not be true depending on the doctor and the patient. You can read more about “medical marijuana” at http://www.drugabuse.gov/publications/drugfacts/marijuana-medicine. This obviously is not a black-and-white issue.

God also created cliffs. It doesn't mean you should go jump off all of them.

I have been doing research for forty years and I do agree with this article because children's brains continue to develop until they are 25-27 years old but this article FAILS to mention two very important FACTS and they are the FACT that

[comment shortened for excessive length] All humans are born with a certain amount of cannabis in our brains and studies show that some of us have lots of cannabis in our DNA and some people have very little but we all have it and it affects our neurotransmitters and lots of other parts of our brains and the latest study on this FACT was done at Stanford and the people who cannot get off the couch when they smoke it or become blithering idiots when they smoke it have an excess of cannabis in their brains at birth and it puts them on overload with respect to a naturally occurring part of their DNA

And people who are born with very little cannabis in their brain DNA react exactly the opposite of the other folks who smoke it and for these people cannabis elevates their neurotransmitters and works better than any anti-depressant which is given to loads of kids and adults in this country and we know that after 20 years of us being the guinea pigs for these mind-bending drugs==== we know the side affects are far worse than those of cannabis

I have taken many IQ tests and no two are the same and I seriously doubt their validity and I have been smoking marijuana for four decades and I still have a menses IQ and at 60 no memory loss whatsoever, so this study is seriously flawed as are most of the tests on marijuana and is not relevant and to this day it is far more effective in treating all the brain destroying diseases and lots of medical diseases and this is why the federal gov. holds the patent for medicinal marijuana for decades and why it is used frequently to treat a myriad of disorders and diseases that most doctors prescribe RX dangerous drugs for==== for all of us---

Learn to period.

why does this site promote lies?

Please, point out all of the lies they have promoted. Then back up your claims with factual evidence from a valid, note-worthy website.

I'm so annoyed seeing ignorant studies like this lol, how can you idiots claim that it is ONLY marijuana affecting the IQ? I've been smoking all throughout high school and now still smoking in college and oh hey guess what I'm doing great in everything.. school, work etc. Guess what else, my dad was a stoner too and scored a 160 on the IQ test WHILE HIGH.. Your research can't prove experiences wrong. To go and make faulty claims as such is offensive. You know that high school kids drink too right? Alcohol doesn't kill braincells either but it sure as hell does slow them down... Go ask those same participants if they consumed alcohol as well during their high school years, because I'm sure those kids who did smoke weed would neeeeverrr go to a party... Did the researchers follow the participants and witness their daily actions, which might not have but could include head traumas etc. Also were they all given the same IQ tests? Doesn't seem like it because you say "other intelligence tests".. don't make me laugh.ha ha what does that even mean? That sounds so uncertain for "professional" research.. I've done plenty of research of marijuana and if everyone knew the truth and stop listening to everything they heard and actually took their own initiative

I'm so annoyed seeing ignorant studies like this lol, how can some idiots claim that it is ONLY marijuana affecting the IQ? I've been smoking all throughout high school and now still smoking in college(heavily) and oh hey guess what I'm doing great in everything.. school, work etc. Guess what else, my dad was a stoner too and scored a 160 on the IQ test WHILE HIGH and I must say, not because of relations, that he is stilll one of the smartest guys I know. I have some friends with similar stories too.. Your research can't prove experiences wrong. To go and make faulty claims as such is offensive. You know that high school kids drink too right? Alcohol doesn't kill braincells either but it sure as hell does slow them down... Go ask those same participants if they consumed alcohol as well during their high school years, because I'm sure those kids who did smoke weed would neeeeverrr go to a party... Did the researchers follow the participants and witness their daily actions, which might not have but could include head traumas etc. Also were they all given the same IQ tests? Doesn't seem like it because you say "other intelligence tests".. don't make me laugh.ha ha what does that even mean? That sounds so uncertain for "professional" research.. I've done plenty of research of marijuana and if everyone knew the truth and stop listening to everything they heard and actually took the initiative to research the drug rather than ignorantly making accusations. One more thing I'd like to add is to research the effects of stress on the human body. Weed is a stress relieved and experience is the best teacher.

Here’s the study published in the peer-reviewed journal, Proceedings of the National Academy of Sciences: http://www.ncbi.nlm.nih.gov/pubmed?term=persistent%20ca... . It’s worth reading – lots of “experience” applied.

 

@Johndoe420 The strengths of the Meier et al study are that it is longitudinal in nature and that it controlled for a number of factors including years of education, schizophrenia, and other substance abuse. That said, it’s true that observational studies in humans cannot account for all potentially confounding variables. Still, personal experience typically provides just one—oh wait, your Dad—two data point(s).  Here’s the back and forth on this --

1.    The original study: http://www.pnas.org/content/early/2012/08/22/1206820109.full.pdf+htm,

2.      The critic’s response: http://www.pnas.org/content/early/2013/01/09/1215678110.full.pdf+html, and

3.      The original author’s response back: http://www.moffittcaspi.com/sites/moffittcaspi.com/files/field/publication_uploads/Response_re_Rogeberg.pdf

Healthy debate is good for science!!

the devilish piece of drugs is that no two human brains react the same, why you and your dad are having a great time....your buddies brain might not Have you never known someone who plummeted on marijuana?
Dear Pot Smokers, Would you want to get on an airplane being flown by a pilot smoking pot? Be operated on by a surgeon who is smoking pot? Have your prescription filled by a pharmacist smoking pot? I personally want the people who keep me safe to have their minds sharp and NOT impaired by drugs.
That makes absolutely no sense, the only way their function could be effected is if they pilot/work while under the influence of marijuana. Which most people are not silly enough to do. Plz Chill out homie.
Yes that would be awesome. the pilot would be epic the surgeon would be relaxed and not jittery and the pharmacist would be nice.
How many deaths have been caused by marijuana?

That is a difficult question to answer.  Marijuana can cause long-term health problems that lead to early deaths, such as lung diseases.  Also, the number of deaths caused by drugged driving (driving under the influence of marijuana) has risen dramatically.  Marijuana was found in the blood of 12% of deceased drivers in 2010 and that number is increasing as recreational and medical marijuana becomes legalized and more accepted.  

Add new comment