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Tuesday 23 December  
Young soft drugs users
Dunedin, New Zealand
Dunedin, New Zealand

Young pot smokers risk permanent damage

Published on : 28 August 2012 - 9:51am | By (Photo: ANP)
More about:

Teenagers who regularly smoke cannabis run the risk of causing lasting damage to their intelligence, memory and attention span. The more people smoke the greater the decline according to a new long-term study of around 1,000 subjects.

The study, carried out in New Zealand by an international team of researchers, is unique because it measured subjects’ IQ at a young age before they used the drug. Some evidence already existed to suggest that marijuana users were less intelligent but it was unclear whether that was the result or the cause of the drug use.

The study followed a group of more than 1,000 people born in 1973 in the southern New Zealand city of Dunedin. Their IQ was measured for the first time at the age of thirteen. They were then tested and interviewed five times in a 20 year period between the ages of 18 and 38. The results of the study, which were published today in the US journal Proceedings of the National Academy of Sciences, show that those who started using cannabis in adolescence and then carried on using it for years showed an average eight-point IQ decline. Stopping or reducing the drug use failed to fully restore the lost IQ.

Those subjects who only began smoking cannabis at a later age did not show a similar reduction in mental ability. Researchers say the results have been corrected to take into account the use of alcohol and other drugs as well as the number of years spent in education.

Reacting to the study,Wim van den Brink,Professor of Psychiatry and Addiction at the University of Amsterdam said it was interesting research but its findings should not be overestimated. Speaking to Dutch daily de Volkskrant he pointed to the results from a sub-group in the study who stopped smoking the week before being tested. The effect on their IQ’s was much less pronounced. “The researchers are right to warn of the consequences of cannabis use at a young age,” he said, “but their results are probably being exaggerated.”


Anonymous 18 September 2014 - 9:45am

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andybruce 30 September 2013 - 7:38am

Smoking also a serious injury for everybody, those people who use the smoke or any other things they face many problem. Most of the people face the cancer disease and sometimes people lost their life so always try to avoid these type of things for a healthy health.

laith 2 August 2013 - 12:24am / jordan

Good article, there is a method used by the and many Nftna which

When you are at least thinking of taking that all important decision to stop this filthy

habit called smoking, you need to write yourself a list. Write down yourself a list of WHY

you should stop smoking and why you have decided to stop smoking.

While you write down your list of your "Why's", I will give you another 2 lists for you to

think about. Here's the first one:

• Straight after the decision to stop smoking, only just 20 minutes after your last

cigarette, your heart rate falls and your blood pressure decreases.

• After the first 8 hours of your last cigarette, the levels of nicotine and carbon

monoxide in your body are reduced by at least half, and oxygen levels return to normal.

• At 24 hours the carbon monoxide is totally discharged from the body.

• 48 hours and there is no more nicotine in your body.

Article source :

Servetus 29 July 2013 - 6:42pm / United States

Marijuana studies incorporating IQ measurements as part of the data adds a variable, not a factor.

IQ test results can vary 20 points or more depending on the mood and desire to do well exhibited by the test-taker. It’s possible to score high one day, while having a bad test day later on. Multiple testing is required given the variability of results, and in checking IQs for marijuana use, multiple and in-depth testing is likely to be inadequate because it’s often assumed by the researchers that one's IQ remains stable throughout one’s live. It doesn’t. Below is a link to just one example of the ongoing IQ controversy:

Malcolm Kyle 19 March 2013 - 5:11pm / United States

Health concerns regarding marijuana tend to come from a self-fueling group of discredited scientists funded by the pharmaceutical, prison, tobacco, and alcohol industries, pushing non-peer-reviewed papers while relying upon reports issued by others in their own group to further support their own grossly misleading research and clearly biased agendas.

Here is a recent peer-reviewed Study proving that Marijuana is not linked with Long Term Cognitive Impairment:

* Nearly 2,000 young Australian adults (aged 20-24) were followed for eight years. It was found that marijuana had little long-term effect on learning and memory, and any cognitive damage that did occur as a result of cannabis use was reversible.
* Researchers categorized them as light, heavy, former or non-users of cannabis based on their answers to questions about marijuana habits.

* Prior studies have found that drug users do accurately report their consumption levels in surveys like this as long as anonymity is guaranteed and there are no negative consequences for telling the truth.

* Participants took tests of memory and intelligence three times over the eight year period the study. They were also asked about how their marijuana use had changed. When the results were at last tabulated, researchers found that there were large initial differences between the groups, with the current marijuana smokers performing worse on tests that required them to recall lists of words after various periods of time or remember numbers in the reverse order from the one in which they were presented.

* However, when the investigators controlled for factors like education and gender, almost all of these differences disappeared. The lower education levels of the pot smokers — and their greater likelihood of being male — had made it look like marijuana had significantly affected their intelligence. In fact, men simply tend to do worse than women on tests of verbal intelligence, while women generally underperform on math tests. The relative weighting of the tests made the impact of pot look worse than it was.

* Researchers then explored whether quitting cannabis would affect the one difference that remained, which was poorer performance by heavy users on a test that required immediate recall of a list of nouns. They found that heavy users who had quit by the end of the study were no longer distinguishable on this measure from those who had never used.
The authors, who were led by Robert Tait at the Centre for Mental Health Research at Australian National University, conclude:
"Cessation of cannabis use appears to be associated with an improvement in capacity for recall of information that has just been learned. No other measures of cognitive performance were related to cannabis after controlling for confounds."
The research was published in the journal Addiction.

Anonymous 6 September 2012 - 4:07pm / Ireland

It doesn't matter because its awesome.

Max Harmreduction 1 September 2012 - 11:46pm

Another study that says it has controlled for the effect of hard drugs - and only the effect of wiet remains as a significant cause. Another study saying that wiet is the most harmful of all illegal drugs. How do we manufacture consent for wiet prohibition, let me count the ways: wiet causes schizophrenia; wiet causes psychosis; wiet causes falling IQ and so on. Like heroin addiction is not a mental illness; like cocaine and methyl-amphetamine psychosis are not mental illness. This fake science suits the political agenda - but telling youngsters these blatant lies encourages them to Step-Up to hard drugs. In 9 years with hard drugs services, run by government, I never saw a single clint who had a problem from wiet that came even a little bit close to what people get from hard drugs

alanposting 31 August 2012 - 6:00pm

A typical Radio Netherlands hatchet job against pot...

Alfonso M 29 August 2012 - 6:50pm

Yesterday I saw this on a segment of BBC's The Hub and it came across as a very biased study, as if it may have been pushed by a Right Wing agenda. The people they interviewed were just [too] "Christian-values" kind of people, one medic vouching for this Daffy Duck study and the other a woman who self-declared to be a strong user who "feels" she lost IQ points because of her SAT results, that she "felt" the urge to smoke cannabis and that she was worried for herself.

Quite a "crock" if you ask me. I was very disappointed, once again, in the BBC for not having both sides of the story.

Take in mind that 40 years ago (when this study began) Christian fundamentalists were very strong around the World, and very specially in New Zealand, where this "team of international [nameless] researchers" began.

I agree that those under 18 should not consume cannabis, alcohol or tobacco, but lets be objective:
1. Who funded this study?
2. Who's in this "international team of researchers"?
3. What was the criteria and methodology used to get to this conclusion?

janv 29 August 2012 - 2:08am / canada

These must be the kids that become politicians then bomb the world into oblivion!

alanposting 28 August 2012 - 8:54pm

"carried out in New Zealand by an international team of researchers"...come on,is that all you got? Smoked pot all my life (65 now), bachelors degree in Sociology, owned and started many successful business and retired with plenty of retirement money....yea, it sure hurt me, of course i wasn't living in New Zealand.

Marco Marboni 28 August 2012 - 2:40pm

Who needs an IQ anyway? If one prefers to be a relaxed and chilled honest person as opposed to an "intelligent but thieving banker", then what's the problem?

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