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Mental Health

Teen marijuana use linked to depression later in life, but what does this mean?

By Rich Haridy
February 13, 2019
Teen marijuana use linked to depression later in life, but what does this mean?
Despite a new meta-study finding a strong association between adolescent marijuana use and later-life depression, experts question whether the link is causal
Despite a new meta-study finding a strong association between adolescent marijuana use and later-life depression, experts question whether the link is causal
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Despite a new meta-study finding a strong association between adolescent marijuana use and later-life depression, experts question whether the link is causal
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Despite a new meta-study finding a strong association between adolescent marijuana use and later-life depression, experts question whether the link is causal

A rigorous new meta-study has for the first time examined the correlation between depression or suicide in young adulthood, and marijuana usage in adolescence. The research concludes there is a statistically significant association between teen marijuana use and depression in later life, but experts suggest caution in determining if the relationship is causal.

We know that marijuana consumption during adolescence is certainly not harmless. A great deal of research has confidently suggested the drug does disrupt the healthy growth of a young developing brain. What this all actually means in terms of any permanent damaging psychological effects is still unclear.

Much research has looked at the connection between marijuana use and significant mental health issues such as schizophrenia, however, the long-term mood modulating effects of the drug are still relatively unknown. This new meta-study collected data from 11 different international studies, collecting information on over 23,000 subjects.

"While the link between cannabis and mood regulation has been largely studied in preclinical studies, there was still a gap in clinical studies regarding the systematic evaluation of the link between adolescent cannabis consumption and the risk of depression and suicidal behavior in young adulthood," explains Gabriella Gobbi, one of the researchers from McGill University working on the project. "This study aimed to fill this gap, helping mental health professionals and parents to better address this problem."

The results revealed that individuals who used marijuana before the age of 18 were 37 percent more likely to develop depression by the age of 35. The numbers relating to suicide risk were even starker, with the researchers suggesting smoking marijuana before the age of 18 was associated with 3.5 times higher risk of attempting suicide in young adulthood.

"When we started this study we expected depression to be a factor attributable to cannabis consumption, but we were quite surprised about suicide behavior rates. Indeed, a significant percentage of suicidal attempts are attributable to cannabis," says Gobbi.

Many experts, while suggesting the research is competent and strong, urge caution when trying to attribute causality. The research is resolutely observational and chock full of limitations. There is no clarity on the amount of marijuana a young person is smoking, the strength of that marijuana, what age they commenced consumption, or whether other drugs such as alcohol and tobacco were also being consumed.

"It's also important to note that these results don't tell us if the effects are specifically due to cannabis use during teenage years," says Lindsey Hines, a scientist from the University of Bristol who did not work on this new study. "It may be that people who were smoking cannabis as a teenager have carried on smoking cannabis as adults, which may explain some of the relationship to mental health."

Another question hovering over the research is that of the relative risk between adolescent marijuana use and equivalent adolescent alcohol or tobacco use. A striking recent study from the University of Illinois revealed heavy alcohol consumption in adolescence caused fundamental changes in the wiring of a young brain that made individuals much more susceptible to psychological problems later in life. Another study revealed heavy drinking during adolescence can result in a smaller hippocampus growth, permanently affecting learning and decision-making.

All of this ultimately suggests that, while marijuana is still primarily illegal in most parts of the world, it is unclear whether it's more damaging to a growing young brain than more commonly consumed, and legal, alcoholic drinks. More research is certainly needed to help better clarify the risk and actual damage that marijuana can wreak on young developing brains, so while we can be sure that marijuana is not harmless to an adolescent brain, we do not yet know exactly how harmful it actually is.

The new study was published in the journal JAMA Psychiatry.

Source: McGill University Health Center / University of Oxford

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Mental HealthMarijuanaPsychologyChildrenDepressionNew Atlas Audio
10 comments
Rich Haridy
Rich Haridy
Rich has written for a number of online and print publications over the last decade while also acting as film critic for several radio broadcasters and podcasts. His interests focus on psychedelic science, new media, and science oddities. Rich completed his Masters degree in the Arts back in 2013 before joining New Atlas in 2016.

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aksdad
It obviously means that smoking pot is bad for you. End of story. How many studies showing the detrimental effects of marijuana do we need before we understand what we've known along? And comparing it to alcohol or smoking cigarettes is as stupid as smoking pot. They're all bad for you. If you want to destroy yourself, take your pick. They'll all do the trick.
Nik
Chicken and egg, cause and effect? Is it the cannabis that causes the depression, or the tendency to depression that causes those with it to try cannabis? My guess is that its the latter. It's also my guess that it's probably caused by dietary trace element deficiencies, and or 'anti-depressant' drugs. As one who has suffered the long term effects of an anti depressant drug, prescribed by a stupid doctor, when I had no need of it in the first place, I can vouch for the suicidal tendencies that they produce. (During this period, I got a craving for dates and almonds, and I found later that both of these contained nutrients that would relieve my problem. So my body knew what it needed, and persuaded me to eat it. If however, I had never eaten dates and almonds, I would have just had an unidentified craving.) If I was cynical, and I am, I would suspect that the purpose of anti depressant drugs is to hook the recipient into permanent dependence on them, to make more money for 'Big Pharma.' Modern 'factory farming' where the same crop is grown on the same land year after year, is bad husbandry of the land, and produces crops that are deficient in essential trace elements, as the land never gets the fallow time for the soils to break down and release them. These missing tiny amounts of nutrients can cause serious defects in human health, and may well be the at the root of the obesity epidemic in the USA. The body demands more nutrients, so the person eats more, but no matter how much they eat, the nutrients are still deficient. These deficiencies in a developing child, and early adulthood, could have lifelong effects, unless they are diagnosed, and compensated for. As most doctors are either ignorant, or are too busy to attend to them, they will go undiagnosed, and untreated, giving lifelong problems.
amazed W1
Just wish the rest of the scientific world would apply the same caution to supposed causal links between correlations. Including even global warming and human activity, though a firmly stated link is probably the only way of getting politicians and John Citizen to behave even remotely sustainably.
Douglas Bennett Rogers
There is a huge anti tobacco campaign along with an equally huge pro marijuana campaign. These two products are almost the same except for the active drug. The main effect of both smokes is emphysema and lung cancer. The active drug is a side issue. The active drugs represent two sides of a cultural war.
Norm.Rhett
Did the research consider the effect marijuana has on physical activity? Exercise is increasingly correlated with healthy brain development and maintenance. Marijuana use has always been associated with physical inactivity, but it need not be so. In moderation it can alleviate some of the pain and boredom of sustained exercise.
jerryd
Fact is depressed kids self medicate with pot which for some of them, isn't good. But the majority have no problems and far better than those alcohol causes, the most dangerous drug. Hasn't 37% of people been depressed at some point, pot or not? Terrible study with far too many variables.
Douglas E Knapp
The causal link is very clear when we are talking about global warming. There are TONS of smoking guns. Only Oil company shills and their idot followers try and push the no global or now the human did not do it fake news. To deny it is about as dumb as saying that the pain in your face did not come from the hand that just slapped you.
When looking at this data we see that they smoked as kids and that they had problems later but what else did they do when smoking? They might and very likely did do other drugs like mushrooms, lsd, ecstasy, niconite, alcohol etc. We also know that people with problems tend to take drugs that make them feel better so depressed teens are very likely some pot. Is pot use the symptom of depression or the cause? So the real question remains, what caused it?
minivini
I don’t have the background to be entirely critical of this study, but as several have stated, it seems like pretty loose dirt on which to build a foundation. The reluctance the psychiatric community has for diagnosing depression, bipolar disorder, bpd, etc in adolescents basically prevents those conducting the study from knowing if these people may have been suffering their adult diagnoses the entire time. To be certain enough of their findings to actually assign a firm percentage to the impact seems almost irresponsible from a scientific perspective.
Cudaboy
When will they stop? This is yet more GARBAGE science. Take away social media from kids and you'll see much less depression - that's been proven but this? Garbage. Nobody has ever OD'd from weed, and of course CBDs are GOOD for you. So pathetic "they" still rant on weed when it's been used for hundreds of years to NO detriment. They even say here - NO CAUSAL CONNECTION - so please stow the phony hype.
Robert in Vancouver
All mental health agencies and medical associations in all G20 countries say inhaling any kind of smoke damages your lungs and using pot damages the brain. They have studies to prove it.
But unscrupulous politicians know they will win the youth vote if they support legalizing pot, just like the Liberal Party did to win the last federal election in Canada.