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The Marijuana and Schizophrenia Conundrum

There’s a connection between marijuana and schizophrenia, and as scholars tease out the chicken-and-egg genetic aspect, they counsel teen tokers to take heed.


Scholars are wrangling with the chicken-and-egg genetic aspect of the connection between schizophrenia and marijuana use. (Dageldog/istockphoto.com)
March 1, 2010 • By • 14 Comments
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For years it’s been a classic chicken-or-egg riddle: Does smoking marijuana lead to schizophrenia, or are those with schizophrenia who use cannabis simply seeking the calming effects of the drug?

Researchers have suspected a link since the 1960s, and study after study has hinted that use of marijuana may trigger schizophrenia, a serious mental illness that affects one in 100 people.

Recent studies, however, provide evidence strong enough to give public health officials — not to mention parents and educators — pause, especially as legalization efforts pick up steam. The latest to weigh in is research to appear in the May issue of the Archives of General Psychiatry. Scientists in Australia followed nearly 4,000 young adults born between 1981 and 1984 at the 21-year mark, and found that the longer study participants had used marijuana, the higher the risk of psychosis-related outcomes. Those who had experienced hallucinations early were more likely to have smoked or used marijuana longer and more frequently.

The study’s authors said there is significant complexity in the relationship: Essentially, those who were vulnerable to psychosis were more likely to use cannabis, which in turn could contribute to an increased risk of developing mental illness.

“The research is conflicting, but the preponderance of the evidence shows that something is there,” said Ken Duckworth, the medical director of the National Alliance on Mental Illness.

If you are a teenager and you smoke marijuana, you put yourself at risk, he said, especially if you have the gene or genes suspected of predisposing one to schizophrenia.

Marijuana is the most used, and abused, illicit drug in the United States, with more than 4.2 million people over the age of 12 reporting substance abuse or dependence in 2008. That is more than twice the number of people who abuse or are dependent on pain relievers, (1.7 million) and cocaine, (1.4 million), the second and third most widely abused drugs in this country.

It is also the most widely used drug among those who have been diagnosed with schizophrenia. In the early 1970s, there was speculation cannabis helped dim the voices and other hallucinations typical with schizophrenia. But researchers started to look at it from the other direction, surmising that marijuana use, particularly heavy marijuana use, may contribute to the onset of schizophrenia symptoms.

In a large study reported in 1987, cannabis use in late adolescence was associated with an increased risk of a subsequent diagnosis of schizophrenia. Studies over the past five years have pinpointed direct connections between brain abnormalities and THC (tetrahydrolcannabinol), the primary psychoactive ingredient in marijuana.

In 2005, researchers at New York’s Albert Einstein College of Medicine used a brain imaging technique called diffusion tensor imaging to study the brains of groups of adolescents for a year. They included healthy non-drug users, heavy marijuana users (daily use for at least a year) and schizophrenic patients. They found that repeated exposure to cannabis resulted in abnormalities in a critical fiber pathway in the brain related to higher aspects of language and auditory functions.

Two years later, in 2007, scientists at Cardiff University’s School of Medicine in Wales found that regular cannabis use among young people increased their risk of developing a psychotic illness later in life by more than 40 percent. And the more they smoked marijuana, the higher the risk. Those who smoked most frequently were more than twice as likely to develop psychosis. Similar results were uncovered by Spanish researchers.

American researchers confirmed those findings in 2009. Emory University doctors reported that teenagers who progressed to daily marijuana consumption experienced psychotic and pre-psychotic symptoms of schizophrenia at earlier ages.

Scientists have known for years that schizophrenia runs in families. Now scientists can point to specific genes, including dysbindin-1, which affects glutamate synaptic function in the hippocampal function area of the brain. The genes neuregulin 1, G72, D-amino acid oxidase, and regulator of G protein signaling 4, or RGS4, have also been implicated.

David A. Lewis, director of the Translational Neuroscience Program at the University of Pittsburgh School of Medicine, and his research team were one of several groups to identify the RGS4 gene in studies of the prefrontal cortex as susceptible for schizophrenia.

In subsequent research Lewis and his colleagues found that gamma-aminobutyric acid, which is an important neurotransmitter required for cognitive processes such as working memory, is impaired by the cannabinoid 1 receptor, which is where THC is activated. In simpler terms, marijuana use impairs the brain’s ability to perform intellectual tasks.

Both of these findings suggest a prefrontal cortex disruption that affects working memory, which is deficient in individuals with schizophrenia, according to Lewis. He hopes further study will ultimately result in drug therapies that will replace the loss of gamma-aminobutyric acid in schizophrenic patients and reduce hallucinations and other symptoms.

But here’s the thing, NAMI’s Duckworth said, once you develop symptoms of the disease, there’s no going back. So why toss the dice by using marijuana?

“It’s quite a chance to take. The uncertainty in the scientific knowledge should not be confused with the risk,” Duckworth said.

Schizophrenia, characterized by serious hallucinations and delusions, is estimated to be the fourth most important cause of life-years lost through disability in the world. And it is irreversible, Duckworth said.

If marijuana consumption continues after a diagnosis, drug addiction is coupled with mental illness and is known in the mental health community as dual diagnosis.

Duckworth said the system is ill-prepared to deal with mentally ill people who are also drug abusers. The mental health system doesn’t know how (or doesn’t want) to treat the drug problem, and the substance abuse health system is ill-equipped to help the mentally ill. Duckworth said he has patients who have been told at drug counseling meetings to go off their psychiatric medications.

“Policymakers are realizing more and more that the [treatment] silos need to be blended,” Duckworth said. But funding comes from varying places, and so coordination is difficult. Sadly, it is the patients who suffer more.

“The dually diagnosed have the worst outcomes,” Duckworth said. They spend the most time in jail, they are the heaviest users of public health and social welfare services, and they die younger than any other cohort, he said.

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When it comes to marijuana use, his advice to teens and parents is simply: Don’t chance it.

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  • captainkona

    “There’s a connection between marijuana and schizophrenia,”

    You’re perpetuating a lie and should be very ashamed. Perhaps you benefit from disseminating this disinformation?

    Those “studies” are paid for by anti-Marijuana interests. I have smoked pot for 37 years (since I was 10 years old. 100% of the people I have closely associated with in those decades smoke also.
    None of them display any side effects of any kind aside from chronic tranquility.

    No credibility whatsoever. No proof is offered aside from the opinions of “professionals” who’s credentials and financial disclosure are impossible for the average person to obtain.

    Marijuana is time tested and proven to be perfectly safe. I highly :) recommend it.

  • Drake4746

    Marijuana “addiction?” Please.

    Association does not prove causation. The studies above have proved nothing.

    Who funded the studies? Why do they want people to turn away from herbal medicine? What do they stand to gain if people purchase more alcohol and pharmaceutical pills as a result?

  • Drake4746

    Furthermore, the lifetime occurrence of substance abuse in schizophrenic individuals is around 40%; with such a high rate of users, there are bound to many that smoke pot. But is pot worse for them than valium, cocaine, LSD, liquor, beer, wine, or caffeine pills? The studies above have no answer to that. Instead, they focus on cannabis–because cannabis cannot be patented, and cannot make any of the big pharmaceutical companies any money.

  • Ron Cuff

    I am puzzled by people who ascribe ill intent to researchers and other scientists who work in the health profession. Could it be THC induced paranoia?

  • DamianN

    Why hasnt the sharp increase in Cannabis use over the past 40 years resulted in a tracked and quantifiable increase overall in schizo cases? If there is a causal link they should track together. They do not.

  • Nice Try But I’ll Pass On Your BS

    Nice propaganda piece. Based on government fabrications and twistings of the truth. I, too, can attest to the fact that cannabis doesn’t do anything but augment one’s life in a positive and benign way. After having used the herb in many different ways over the years, with friends and family, all of whom are upper-middle class, healthy and happy, I can say that “news stories” such as this one are rife with lies, prejudice, hate, greed, and pure corporatism. They’re paid for by alcohol and pharmaceutical companies, if not written by people who work in or for those companies. Or, they’re created by law enforcement, prison owners, drug cartels, or groups like “Partnership for a Drug-Free America”, all of which (and more) gain billions of our tax dollars each year on this morose war on the American people.

    Don’t believe the lies. Wake up from the nightmare that is drug prohibition. Realize the truth and talk about it, make everyone you know aware of the charade the government has played on us, vote OUT those who support being “tough on crime” by being evil on drug users. It’s time to end the hypocrisy and eliminate the true source of social disease in this country – the disease created by the War on Drugs.

    WAKE UP AMERICA

  • Sam

    LEGALIZE IT!

    Assuming theses studies aren’t hogwash-propaganda,
    or bogus & skewed due to funding from Anheuser Busch or Marlboro, I’d still choose schizophrenia over the stress and boredom of a life without weed!

    MY BODY MY CHOICE!!

    Rise up and fight your oppressors!

  • Bill Harris

    Prohibition causes schizophrenia. One need not travel to China to find indigenous cultures lacking human rights. America leads the world in percentile behind bars, thanks to the ongoing open season on hippies, commies, and non-whites in the war on drugs. Cops get good performance reviews for shooting fish in a barrel. If we’re all about spreading liberty abroad, then why mix the message at home? Peace on the home front would enhance global credibility.

    The drug czar’s Rx for prison fodder costs dearly, as lives are flushed down expensive tubes. My shaman’s second opinion is that psychoactive plants are God’s gift. Behold, it’s all good. When Eve ate the apple, she knew a good apple, and an evil prohibition. Canadian Marc Emery is being extradited to prison for helping American farmers reduce U. S. demand for Mexican pot.

    The CSA (Controlled Substances Act of 1970) reincarnates Al Capone, endangers homeland security, and throws good money after bad. Fiscal policy burns tax dollars to root out the number-one cash crop in the land, instead of taxing sales. Society rejected the plague of prohibition, but it mutated. Apparently, SWAT teams don’t need no stinking amendment.

    Nixon passed the CSA on the false assurance that the Schafer Commission would later justify criminalizing his enemies, but he underestimated Schafer’s integrity. No amendments can assure due process under an anti-science law without due process itself. Psychology hailed the breakthrough potential of LSD, until the CSA shut down research, and pronounced that marijuana has no medical use. Former U.K. chief drugs advisor Prof. Nutt was sacked for revealing that non-smoked cannabis intake is scientifically healthy.

    The RFRA (Religious Freedom Restoration Act of 1993) allows Native American Church members to eat peyote, which functions like LSD. Americans shouldn’t need a specific church membership or an act of Congress to obtain their birthright freedom of religion. God’s children’s free exercise of religious liberty may include entheogen sacraments to mediate communion with their maker.

    Freedom of speech presupposes freedom of thought. The Constitution doesn’t enumerate any governmental power to embargo diverse states of mind. How and when did government usurp this power to coerce conformity? The Mayflower sailed to escape coerced conformity. Legislators who would limit cognitive liberty lack jurisdiction.

    Common-law holds that adults are the legal owners of their own bodies. The Founding Fathers undersigned that the right to the pursuit of happiness is inalienable. Socrates said to know your self. Mortal lawmakers should not presume to thwart the intelligent design that molecular keys unlock spiritual doors. Persons who appreciate their own free choice of path in life should tolerate seekers’ self-exploration. Liberty is prerequisite for tracking drug-use intentions and outcomes.

  • HisMother

    This is not just an academic question for me, since my son was– as we discovered–growing his own and pretty constantly stoned for an entire year, culminating in his arrest for murdering my cousin. (This was NOT, by the way, a drug deal gone wrong, but my son’s paranoid delusions played out). I’m astonished by the vituperative (and dare I say paranoid) comments from pot smokers–who have the audacity to think of themselves as “mellow”! We still need much more research, but it’s obvious there’s a link between marijuana and schizophrenia. It’s still unclear whether marijuana use is cause or effect. I’ve been more inclined to see it as an attempt at self-medication, but I’m willing to consider other arguments, based on good research. BTW, the source of research grants are usually a matter of public record.

  • wakker

    This article is quite balanced IMHO. In many other media this study is directly presented as “proving” a direct causal connection, whereas here it is clear that there is some link but it is not so clear (yet) what the exact causes and effects are.

    I’m a cannabis user myself, for over 10 years but only once or twice a week. As with most things, one has to control one selves and overdoing something is never good, be it alcohol or cannabis. Alas for many youngsters in particular self control is very hard. We see it all the time with alcohol and also sometimes with cannabis. It’s not physical addiction, but habits that may be hard to break. Others can have equally damaging addiction w.r.t. computer gaming, internet or sex. I could imagine that constantly being stoned might change ones mental health in the long run.

    I feel with “HisMother” and applaud you for still having a balanced view in spite of what happened to your family. Many ppl in your situation would blindly blame cannabis; and while I don’t agree, I can even understand such a reflex is something of this magnitude happens.

  • Chris

    After looking at some of these papers with my training in statistics and econometrics, it seems to me that these researchers have been very careful in qualifying their results. As a former heavy pot smoker from about 14 to 21 (1-2 grams/day), I have never had any psychotic symptoms, but I do have one friend who does, and he happens to be a friend who smoked a lot of pot. That does not mean anything, but clearly brain development is impacted by any psychoactive drug. Note, the schizophrenia risk in the general population is only 1%, so doubling that is not still not very significant. However, if a parent has the disease, your risk is 10%, and now the possibility of doubling that risk seems concerning.

  • Ajax the Great

    Here we go again, Reefer Madness redux. At least this article does not claim the study is conclusive proof. Correlation does not equal causation. Also, the study did not look at how heavy the users used cannabis. The best anyone can say is that jury is still out.

    Cannabis use has skyrocketed from virtually nil (about 50,000 users) in the 1930s-1950s to over 50 million users today. The average age at first use has dropped over the decades as well. And at least half of all adults under 65 have tried it at least once in their lives. I have always wondered why, if there was a significant causal link, why hasn’t there been at least a modest increase in psychosis?

    If a truly causal link really exists, it must therefore be only for a very small percentage of the population–those who began using before 15 (or whatever age) AND used very heavily (i.e. daily) for years AND were predisposed to psychosis AND possibly some other factor. Or, it could simply be that it does not cause cases that would not otherwise have occurred. It may precipitate cases that would occur anyway, or it could just be due to a common vulnerability with varying orders of onset. The latter is what I believe is the most likely explanation in light of this and other studies done on the matter.

    Thus whatever it is, it does not appear to be of major public health significance. Perhaps it may be significant at an individual level (if it were truly causal), but not at a population level. And it certainly does not justify continued prohibition of cannabis–a policy that clearly does more harm than good. Meanwhwile, we ignore the pink elephant in the room–booze.

  • Liz

    I was interested in this article and many others around cannabis linked to schizophrenia. I would like to see an objective debate around specific types of cannabis and drug induced psychosis. As as old ASW now Approved mental health professional (Mental Health Act 1983 amended 2007), I have been involved with a number of admission under section of the mental health act because of drug induced psychosis primarily due to lack of insight, and such levels of distress and psychosis, their safety and sometimes the safety of others needs protectig for assessment and or assessment and treatment. I have seen an increase in people coming through the criminal justice system because of their distorted belief system and paranoia and yes what I do know from first hand experience is that many people once in hosptial and away from Cannabis find their psychosis vastly improved (mainly without anti-psychotic medication). I have seen the same people once released repeat the same patterns. I still feel however, that if we really want to unpick the issues, starting from a base line that cannabis causes schizophrenia is unhelpful and counterproductive. In my very humble opinion, a correlation between some types of skunk weed and drug induced psychosis on certain individuals maybe a better place to start. In my 15 years involved in sectioning patients, I always ask if they may have used and I can truly say that although I dont use cannabis myself (I use other legal substances such as alcohol) I have never had to section someone who says they ‘grow and use their own’.

  • BBeard

    I am a past casual to heavy user of pot, and am predisposed to think it is mostly harmless. So that's my bias.

    This article goes to some lengths to seem unbiased, but the anti-marijuana bias does come through. One of the common, subtle biases are the words "use" and "abuse". The anti-pot side conflates "abuse" and "use", which we see in the following quote. To use is to abuse. All use is abuse. Now consider the same language with alcohol. Is going out for a drink abuse? Is having a glass of wine with dinner abuse? I think you know the answer, and I suspect you therefore know the bent of the author.

    "Marijuana is the most used, and abused, illicit drug in the United States, with more than 4.2 million people over the age of 12 reporting substance abuse or dependence in 2008."