Report: There Is No 'Safe Level' Of Teenage Cannabis Use

An Australian-led research report studying the effects of marijuana on adolescents has painted a hairbrained picture of the nation's school-aged potheads. According to the study, teens who toke daily are 60 per cent less likely to complete high school or university compared with those who have never used. In addition, the researchers claimed there was no "safe" level of cannabis use, although the risk of adverse effects does increase with the frequency of usage.

An international research team led by the University of New South Wales' National Drug and Alcohol Research Centre analysed the effects of adolescent cannabis use via three large-scale studies: the Australian Temperament Project, the Christchurch Health and Development Study, and the Victorian Adolescent Health Cohort Study. Collectively, this totaled 3,700 cannabis users.

The study found that cannabis-use in teens often leads to a range of problems in young adult life, including mental health problems, increased substance use and reduced educational attainment:

We recorded clear and consistent associations and dose-response relations between the frequency of adolescent cannabis use and all adverse young adult outcomes. After covariate adjustment, compared with individuals who had never used cannabis, those who were daily users before age 17 years had clear reductions in the odds of high-school completion and degree attainment, and substantially increased odds of later cannabis dependence, use of other illicit drugs, and suicide attempt.

If the results are to be believed, adolescents who use cannabis daily are 60 per cent less likely to finish high school and seven times more likely to attempt suicide. They are also 18 times more likely to develop a cannabis dependence and eight times as likely to use other illicit drugs in later life.

It's worth noting that the risks increase with the amount of the drug being taken, although the researchers stressed that there was no usage level at which no risk was present.

The report concludes that prevention or delay of cannabis use in adolescence is likely to have broad health and social benefits. Efforts to reform cannabis legislation should therefore be carefully assessed to prevent potentially adverse developmental effects among teens.

Cannabis is currently the most widely used illegal drug in Australia, with around four per cent of 14-19 year olds using the drug at least once per week.

Young adult sequelae of adolescent cannabis use: an integrative analysis [The Lancet]


    Is the results are to be believed, adolescents who use cannabis daily are 60 per cent less likely to finish high school and seven times more likely to attempt suicide. They are also 18 times greater chance of cannabis dependence and are eight times as likely to use other illicit drugs in later life.

    Correlation is not causation.

    Considering it would be a breach of ethics to actually provide varying doses of cannabis to a statistically diverse group with a control then this is just collating data from teens who already form these habits.

    The kids who hang out at the back of the school smoking tobacco for the last century were probably also much less likely to graduate, does that mean tobacco use prevents kids from academic achievement? Or could it possibly just be symptomatic of the individuals own social path?

    Of course like all drugs there are negatives, but there seems to be a rather large jump being made here from that correlation of data to causation.

    Disclaimer: I've only read the portion of the study you quoted.

      I don't see any claim of causation here, just that there's an association between cannabis use and dropping out of school and suicides. It's likely that these three things are all symptomatic of a certain type of socio-economic environment, upbringing, and individual mental state.

        How about with the portion I quoted?

        Or the headline? How about another quote:

        The study found that cannabis-use in teens often leads to a range of problems in young adult life,

        Definitely suggests a causation, as does:

        The report concludes that prevention or delay of cannabis use in adolescence is likely to have broad health and social benefits.

        Might want to read things a bit closer before calling somebody out.

          The portion you quoted, and to which I was replying, has no claim of causation. Read it again. "Likelihood" is not causation.

            There's heavy inference however and a distinct lack of alternate viewpoints/interpretations of which there are many. It seems like his specific claim of "causation" may not technically be correct yet it heavily infers it with the language used. The average person needs to work extremely hard to actually unpack the information in this study.

            That's what he's getting at.

              "The average person needs to work extremely hard to actually unpack the information in this study."

              That's because scientific reports aren't written for "the average person". This is the danger of lay people reading scientific reports; the opportunity for misinterpretation is huge. Especially when you only read an article about the study written by a journalistic third party, or are restricted to reading the abstract. Terms as used in science often have different connotations than the same terms used in every day language.

              Last edited 10/09/14 5:20 pm

                But this article is written for the average person.

                And this study's recommendation and conclusion does suggest a causative link as being likely.

                If the actual study doesn't then it's another failure on the part of this article and it's author.

                  Without reading the entire original study (not just the abstract), we can't comment on whether the researchers did or did not identify a causative link, and whether this conclusion was valid. However it should be noted that nowhere in the abstract do the researchers imply a causal link. The terms used are "associations", "relations", "odds", "likely", and "potentially". Therefore Chris was mistaken to use terms like "leads to" in his article as this implies causality, and has obviously lead to a lot of confusion as to the actual findings of the study by people who may only read this article. It is, as you put it, a "failure on the part of this article and it's author".

                  I'm guessing that like most journalists, Chris doesn't have any scientific background. As a scientist myself, the misrepresentation of scientific findings by the media is a huge peeve. I usually completely disregard whatever a journalist writes about a study and instead go straight to the source when I can.


            Likelihood is a suggestion of probability. If you are suggesting that teens who smoke pot are likely not to graduate then you are saying there is a likely causation there.

            Of course if you want to just harp on the fact that I didn't pick out the absolute best quote to illustrate that fine.

            Look at the headline or the other two quotes I sent, the entire tone of this article is suggesting a causal link.

              "If you are suggesting that teens who smoke pot are likely not to graduate then you are saying there is a likely causation there."

              No you're not. You're saying there's an association, which is different. For example, statistically, living in an African country increases your likelihood of contracting AIDS. This doesn't mean that living in Africa causes you to get AIDS. You're just projecting your own interpretation of what "likelihood" means, which is different to what it means in science and academia.


                The headline specifically says that pot is dangerous. The article says cannabis use leads to (read causes) a range of problems and it's conclusion is that removing cannabis will have a direct effect once again suggesting causation.

                If the entire article is referencing this causation and the says "teens who smoke pot aren't likely to graduate" then the information imparted in the rest of the article colours that from a correlative statement (Which in isolation it would be) into an examination of causation.

                Big surprise, the context actually matters and alters the meaning.

                Which is why I chose two more direct quotes when you first had a problem with my argument, now stop attacking the initial choice of quote and perhaps actually taking the argument on it's merits?

                Also my interpretation of likelihood is accurate, as I said it's a measure of probability and it has no inbuilt connotations to either correlation or causation.

                Also for your aids argument, if I wrote an article with a headline:

                There is no safety from AIDs when visiting Africa
                "We recorded clear and consistent associations between length of time spent in Africa and the incidence of AIDS. Those in Africa show an X% rise in AIDS related incidents."
                If this study is to be believed people who visit Africa are Y% more likely to contract AIDS, the study recommends that prevention or delay of exposure to Africa will likely have broad health benefits.

                Now nothing is technically lying in that faux article, it lists a whole load of correlative information without addressing any actual underlying cause. Yet I still imply that there is a direct cause from that information and suggest a solution that although effective in it's stated goal creates a misconception about the real cause that could be dangerous.

                If I went by that article and just avoided Africa but went out enjoying unsafe sex... By ignoring underlying causes and educated to mitigate those the information about increased AIDS rates in Africa is literally useless.

                This is why media using correlative studies and awful headlines is an issue which should be called out. My first comment was because this was all correlative information being used to imply causation, by not openly saying that it's as good as actively deceiving readers.

                Last edited 10/09/14 5:33 pm

                  "This is why media using correlative studies and awful headlines is an issue which should be called out."

                  Agreed. I think we were getting confused as to whether we were talking about this article or the original scientific study. As I said in my reply to your other comment, this article is very poorly written from a scientific standpoint.

                  Essentially, @chrisjager is being the "News Wire Organisation" in this cartoon:

                  Last edited 10/09/14 6:25 pm

      Thats funny, because I only read the portion of the study quoted and thats the first conclusion I came to as well. Although honestly I would be quite surprised to see any research based on correlation being causation not to mention from a University.

      It just seems like they are taking data an interpreting it in a singular way, when I went to school it was usually the kids that never wanted to study that turned to cannabis for something to do. It wasn't the fact that they started using cannabis which made them study less, especially how most of them didn't study at all.
      It was also not surprising that the kids with difficult family issues were also the ones that were usually more likely to try drugs, smoke or be depressed. Of course again here correlation doesn't mean causation, but I'm just trying to show that there is typically many factors for the reasons supplied above that makes this difficult to believe.

      This isn't always true of course, but its sounding more of an "anti drug campaign" as opposed to any sort of appropriate research. (based on what I am assuming anyway).

        Look information like this is important. It should be a call to action for more study.

        What it shouldn't be used for is an indictment of a drug based on circumstantial evidence. The fact one of the supporters is a "Temperance Project" also makes me feel like there is a bias in how this is being analysed.

    Unless they conducted this study by going up to 3700 random teens (covering the whole socio-economic spectrum and who didn't already smoke weed erryday) and providing them with daily marijuana I'd dispute the results of this test..

    Last edited 10/09/14 3:22 pm

      Why? Of course you can't actually be supplying adolescents with marijuana because that'd be unethical. But that doesn't mean the results of the study can be dismissed. 3700 is a pretty good sample size for this type of longitudinal study. And without reading the original report I can't comment on whether they controlled for things like socio-economic background, but it seems to be a pretty obvious thing to do if they had that information.

        Because it's not scientifically rigorous to determine a causation in this situation.

        As I mentioned above, it doesn't mean this study is worthless. It's valuable information and should be used to direct further research.

        But if you don't have a blind control group it's useless* for determining what caused these effects in real life.

        *By eliminating other factors in other similar studies you can create a more accurate guess at causation.

    You can paint it with whatever brush you like, but it stands to reason, that preventing kids from starting in the first place, can only be a good thing..!

    I can only assume @vumnoo is a toker from early on...

    Last edited 10/09/14 3:24 pm

      I'd prefer it if we just educated kids on the facts with no biases involved. If they're old enough to make the decision to start smoking weed then they're old enough to understand what cause and effect is.

    Everyone complaining about correlation versus causation, or complaining about sampling, should read the methodology employed: they looked at people with widely varying cannabis use (from nothing to daily) and broad outcomes (education, drug dependence, mental health, etc.)

    They also used multi-variate analysis, as indicated by the reference to "covariate adjustment" in the "Findings" section. If they chose good controlling variables, then their multiple regression analysis would allow them to infer causation with a high degree of confidence.

    With good multi-variate analysis, concerns such as the above are unfounded. So, it all depends on whether they chose good variables. And, considering the sheer number of PhDs involved in this study, I'd say that's pretty likely.

      The study can be good, it doesn't mean the conclusion isn't biased.

      There's probably a lot of good information in the full study that is invaluable in learning more about it's use, but it's impossible to determine causation without a control group in this kind of study.

      "People who smoke pot are less likely to graduate" is an important scientifically backed up piece of information.

      "Pot causes you to be less likely to graduate" however is an opinion with almost no basis in fact.

    Abbott: "Reefer Madness" now mandatory viewing in high schools.

    From the outset, I don't believe teenagers should have access to cannabis.

    With that out of the way, two of the three studies this study sources data from have been discredited with not looking at other factors such as socio economic, child abuse or other trauma. Correlation is not causation.

    From the following article:

    "There are also other factors — such as child abuse or other trauma — that might lead people to seek escape in heavy marijuana use and could also affect brain function. Meier and her colleagues did not examine these factors but say it’s possible that such elements could explain the results better than marijuana itself.

    If the link is real, the effects on cognition could be dramatic. But intelligence and cognition is affected by a plethora of other factors, including genetic, social and environmental influences that may supersede any influence from drug use. Despite the fact that the average marijuana user starts at age 17 in the U.S and nearly 7% of high school seniors currently smoke pot every day, IQ scores have risen tremendously over time in all developed countries in recent years. Most of those same countries also experienced a massive increase in marijuana use between the 1950s and today."

    Even if there is a clear link between teen cannabis use and bad outcomes, this is exactly why cannabis needs to be legalised. A pot dealer doesn't ask for ID. A regulated industry where licenses are hard to get and easy to lose will go a long way to restricting access.

    Statistics out of Colarado and Washington are showing that teenage use is dropping since the introduction of legal recreational sales.

      Couldn't agree more. With regulation comes legal age constraints. Like anyone would ever make it legal for teens!

      With that being said, I'll have my bag of legal cannabis now please.

    I want to point out me not finishing high school had nothing to do with my weed smoking.........

    @Dman, since the thread is full.

    I think we're finally on the same page, don't want to read too much into the study since I haven't read it. But yet the information is good, I'm just touchy at the recommendation (Which I'm assuming was accurately reported) and the article itself which jump into an implication of causation.

    Good study, just need to be careful what we take away from it. Also @thecog brings up the point that this study is based on stats from two other studies which were criticised for ignoring other contributing factors.

    Edit: I love that comic by the way, and it makes sense you'd come in to defend the science. It's my fault for being too lazy to follow up on it, despite knowing full well how accurate that comic is.

    Last edited 10/09/14 6:34 pm

    bud is for champions

    So here's the thing - I went to a 'selective' highschool in Sydney (our year happened to be the first 'selective' year through, which made for 'interesting' relations with older years). By 10th grade I'd say 50% of our year were smoking weed occasionally, and by year 12 graduation I'd wager a good 90% had tried it at least once, with at least a third if not more including myself using fairly regularly (in the range of a few times a week, though not every day). I went to uni and got my BA, then a post-grad, and since then have gone back 2 times to 'Vocational' RTOs for an AD & a CertIV. Making me the most over-qualified Digital Adops manager you'll find :-) Most of the peeps from my school year are similar - we have guys and girls working overseas in various fields, or making a success here, most went to uni, and probably I'm one of the LEAST successful ones (maybe because I studied TOO much, or maybe just because I'm a dick as LH / Giz commenters would know).

    What's my point ? We know 'chronic' i.e daily marijuana use 'impacts' ADULTS, so it should be absolutely a no-brainer that it has the same effect on teens. But I would argue my school year demonstrate perfectly that you CAN have a 'safe' level of use without causing any long-term impacts to learning or life outcomes.

    EDIT: I should point out I haven't had a toke since 2000 which was the year I got out of uni. Which puts me perfectly in the 'teen user' (and early 20's) bracket we're looking at here

    Last edited 11/09/14 9:01 am

    how about regulate it and not allow those under 21/18 to purchase it? from personal experience it was 10xs harder for my friends to get alcohol from a secured shop than cannabis from the seedy guy around the corner

    I'm just going to leave this here;

    That's all... Move on.

    This is a really biased article - against teenagers. I think that it's important to make it clear in what situations teenagers are using or even abusing marijuana. But in my honest opinion, a little bit never really harmed anybody. If you see some of the patients who benefit from using cannabis for medicinal purposes, a lot of this article would be made redundant!

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