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40-year Study Shows Effects of Cannabis on Personal & Professional Lives

40 Year Study of Effects of Marijuana
Photo by Fernanda Armijo

Joint Opinions

40-year Study Shows Effects of Cannabis on Personal & Professional Lives

There is plenty of proof that alcohol use is much more dangerous than cannabis use. You can’t overdose on marijuana and it doesn’t cause direct death. On the other hand, alcohol is more addictive, can increase a person’s risk of injury and is linked to cancer and brain damage. And the health costs associated with alcohol use is eight times higher than it is for cannabis use.

But a Clinical Psychological Science study released today claims that the results of heavy cannabis use on a person’s life are similar to alcohol abuse  — and in some cases, it’s worse.

While marijuana use may not have the same physical consequences as alcohol, an international team of epidemiologists and psychologists found that it still affected the personal and professional lives of habitual users. They found that when users smoked cannabis four or more days of the week, they ended up with low-paying, low-skilled jobs more frequently, and it could also lead to “antisocial behaviors at work,” like stealing money and lying to get a job. At home, frequent cannabis use was often tied to physical and emotional abuse of the user’s partner.

These effects are similar to those found in people who abuse alcohol — except cannabis users were found to have more financial difficulties. And the longer they used cannabis at a steady rate, the worse their lives got.

While its results “[do] not support arguments for or against cannabis legalization,” according to Magdalena Cerdá, the epidemiologist at the UC Davis Violence Prevention Research Program who led the study, “it does show that cannabis was not safe for the long-term users tracked in our study.”

The team of researchers included doctors at UC Davis, Duke University, Arizona State University, Kings College London, and the University of Otago in New Zealand. They followed about a thousand children from all socioeconomic groups born between 1972 and 1973 in Dunedin, New Zealand, following up every two to six years. Information was culled from questionnaires, as well as from credit ratings, court records and government social-welfare benefit records.

Of the participants, 18 percent were considered marijuana dependent at some point during the study. Another 140 were categorized as regular cannabis users at least once over the years.

“Alcohol is still a bigger problem than cannabis because alcohol use is more prevalent than cannabis use,” Cerdá said in a press release. “But, as the legalization of cannabis increases around the world, the economic and social burden posed by regular cannabis use could increase as well.”

While the breadth of the study is unprecedented, it’s important to note how New Zealand’s attitude toward marijuana differs greatly from that in the United States. Under the country’s Misuse of Drugs Act of 1975, possession of any amount of the drug is illegal. Supplying and manufacturing marijuana can bring a 14-year jail sentence, while planting and cultivating it can land you anywhere from two to seven years in prison. Even so, it’s the most widely used illegal drug in the country.

There has been a slow movement toward medicinal use in the country, but there’s been little research into its benefits.

Read the full study here.

Do you agree with the results of this study? Let us know.



  1. Toni Priore

    April 25, 2016 at 2:54 pm

    I have MANY friends who have smoked cannabis since they were 14 years old. They all are productive members of society. They hold down jobs own houses and have incomes of over $75,000 They have good job(after all what bad job pays over $75,000? They donate to charities have saving accounts and are still smoking many times DAILY! So please forgive me if I can’t believe this study! I use medical marijuana daily for a medical condition but I believe it should be legal and I always have except when I believed the BS the government put out about it. Yes I thought it was “of the devil.” Funny how if you open your mind and see how things really are you can change your opinion!

    • Toni

      April 25, 2016 at 2:57 pm

      And just so you know I myself am 59, many of my friends who smoke regularly are also over 50…. So tell me again what happens to people who smoke regularly?!?!?!

    • Sen Darbi

      May 29, 2016 at 10:20 am

      I smoked marijuana a lot years ago, every day for several years. It trains you and habituates your mind into a non productive state of denial about reality. That’s why Robert Downey, Jr. said it was probably the most insidious drug. Instead of dealing with life on its own terms, you get high. Classic addiction behavior. Makes it hard to get anywhere. I see so many long term stoners who are just so weak mentally, so lacking in the mental will to think deeply and with a long attention span, and without much ability to apply themselves. It’s not black and white, it’s a matter of degree. But the 40 year study in this article is not news, we’ve been watching it happen all along. And here’s the kicker—when you’re consistently smoking marijuana, you can’t see your own failings. You think you know, but you don’t know. You’re self-deluded. Personally, I don’t want employees who smoke dope regularly. It subverts the human personality, and they just don’t measure up in positions of serious responsibility.

  2. Candace Tromblay

    April 12, 2016 at 8:13 am


  3. derylrobinson

    April 4, 2016 at 6:52 am

    This report just confirms what anyone who is alive and looks around already knows. If you are successful in life while being a regular pot smoker, you are an exception. How do you know you wouldn’t be even more successful without it?

  4. troy

    April 2, 2016 at 9:14 pm

    the financial thing is what makes me laugh the price of cannabis is so high because as it isn’t legal it is sold basically black market as a long time licenced Canadian grower I can state without a doubt that under a legal system where any citizen can produce there own cannabis they will find the price to produce cannabis after the initial out put for growing equipment is less then $1 per gram but its street price is $10 as well as the licenced producers who are setting the prices based on the current value of cannabis under a legal system that makes it illegal , I personally feel that the law should make cannabis completely legal to use and grow for everyone , the big companies will still make money as not everyone has the time or the initiative to grow all the time so they will still buy from the new big companies that will come along but it will just be like how beer can be made at home .

  5. Allen Mitchell

    April 2, 2016 at 5:38 pm

    idiots the lot of ya!

  6. Chris Wierzbinski

    April 2, 2016 at 3:01 pm

    Uhhhh….id have a bunch of followup questions about the people involved in this study……because I see the opposite 95% of the time…

    # more propaganda

  7. Paulpot

    April 1, 2016 at 6:44 pm

    New Zealand was all you had to say. NZ is obsessed with proving cannabis is bad M’kay. The NZ people have one of the highest rates of cannabis consumption in the world and a very prohibition oriented government dedicated to proving its right to destroy its people lives. The NZ govt is committing serious cries against its people so they have to make up these lies to save themselves from being prosecuted. And its very easy to do. You crush the lives of cannabis consumers and then you write up a paper that says that all the damage you did to people was really their own fault for consuming cannabis. Prohibition is a self fulfilling prophecy so long as you never let the victims space to tell their side of the story.

  8. Allen Mitchell

    April 1, 2016 at 8:13 am

    half of the pot heads out there are lazy and got no motivation to do anything, i know because i was one once… for 15 years, if used right can be fine buts its like anything have to much and it turns into a bad habit. my daughter is what made me stop me smoking a few grams a day but once in awhile i might have a puff to relax and have fun as i don’t drink or do anything else, but i was dependent on it in my prime and never thought i could quit, now i don’t even think about it. I’m sure i have over done my usage and will quit fully soon

    • Nik Schumacher

      April 1, 2016 at 2:40 pm

      Most I know are like me, highly educated, highly tecknickle jobs and degrees, non violent, many are veteran musicians. Your artickle is totally Bogus and without any Real substantiation other your claims that the study was done by educated Knowledgable people. Bullshit! NO real experience? Not qualified to have any opinion. End of story!

      • Allen Mitchell

        April 1, 2016 at 10:24 pm

        most are not like you and the ones like you prob smoke stuff all, I’ve seen the bad side effects of it all to much, i don’t think it should be banned but also not gonna deny the bad side effects because they’re true… i dont think your qualified to have a say if your so 1 sided because you smoke and want to defend it because of it, I’ve been on both sides of the coin and have 15 years experience smoking heavy 3 or more grams a day and seen both the bad and the good, but my point it you cant ignore the bad and reject because you don’t want to listen to the truth

      • Thakur Aman

        April 2, 2016 at 1:16 am

        the researchers are a way behind the truth Nik

      • Toni

        April 25, 2016 at 3:06 pm

        I know many people who are musicians and who have smoked regularly since they were 14, they are now in the 40’s, 50’s and 60’s and are very talented, artistic and extremely brilliant! So what has happened to them? Maybe they should find real users who have actually been smoking daily since the 60’s and 70’s and see what’s going on with them. I bet they will find these people are doing better than most!

  9. erik

    April 1, 2016 at 8:06 am

    Causality or correlation, that’s the real question.

  10. shmuelman

    March 31, 2016 at 9:58 am

    So, if people are using cannabis for decades, all the use was illegal. So how does legalizing or keeping it illegal change anything? As the government says, “sends the wrong message.” So they send you a prohibition message at the end of a gun, and that’s the right message?

  11. Tony Aroma

    March 26, 2016 at 4:55 pm

    I have an equally valid title for that study: Persistent economic and social problems represent risks for cannabis dependence and alcohol dependence. Correlation does not equal causation.

  12. Sensible Moderate

    March 24, 2016 at 9:01 am

    It’s odd that this exact same story is published on WebMD, Newsweek, New York Post, U.S. News and World Report and but none of the above mentioned sourced allow the ability to comment.

    Personally, I have “abused” marijuana, since pre High School, played sports, have a degree from a prestigious university, and a solid career path. I take full offense to this negative PROPAGANDA.

    Coincidently, I was able to deduce that “lead researcher Magdalena Cerdá, from the University of California, Davis” is an associate professor who is paid to interpret these findings. Perhaps an organization like the National Institute on Drug Abuse has paid for this research. NIDA’s official mission is to fund studies to find harms in cannabis — not any benefit.

    The organization was established in 1974 and has an annual budget of $1.04 BILLION dollars to (perhaps) incentivize these claims. It’s no coincidence that these reports, “suddenly” appeared yesterday and today in the mass media. These will be the same claims that we hear in arguments for prohibition in the upcoming months.

    • Stel-1776

      March 24, 2016 at 4:06 pm

      The lead author of this study received funding from the NIDA:

      “M. Cerdá was supported by a grant from the U.S. National Institute
      on Drug Abuse (DA030449)”

    • Allen Mitchell

      April 1, 2016 at 10:19 pm

      not all people can have what you have smoking weed, im not saying it should be banned but don’t ignore the effects it has on some people because it does! theirs many factors to look at, how much you smoke, what you do in life, i smoked really heavy for 15 years and almost half that time i had no motivation to do anything else but smoke bongs all day long, i became lazy and it was because of my weed habit, the area i lived in there was a huge pattern of the same lazy, not motivated docile losers because of weed. but I also no a lot of people who don’t smoke a few grams a day or more and are very good on it and prob wont effect them at all, some people like to drink and are fine but others are not, its all about balance and think people shouldn’t ignore the bad side effects it has on some people just because they want to defend what the believe in, looking at the bad doesn’t mean I think we should have it banned, i think it should be legal but we cant ignore how some people are on it

    • Bill Coleman Dean

      April 2, 2016 at 5:59 am

      the same kind of study came out from a psychologist who said he can guarantee that marijuana use causes schizophrenia. But, the same story, his studies, costs in the billions, was funded by all these groups whose sole purpose is to prove that marijuana causes damage. So of course this story came out in every popular newspaper. Because they have just been waiting for some kind of negative connotation. And theyre owned by the same person or people. This is their Lifeline 2 more money. We know the truth is, it says marijuana users generally have less money, of course, because I have to pay outrageous money for marijuana. I myself spend about 200 a week. That’s ten thousand a year. Been doing it for 20 years. And I live in $1,000 trailer and drive thousand dollar vehicles. Imagine what I could have done with all that money if I could have just grown my own plants the whole time.

  13. Ricky

    March 24, 2016 at 8:17 am

    “They found that when users smoked cannabis four or more days of the week, they ended up with low-paying, low-skilled jobs”

    Classic correlation causation argument. Why wouldn’t people with crappy, low paying jobs want to escape with some cannabis to end their day?

    “except cannabis users were found to have more financial difficulties.”

    Yep, criminal records for drug use make it hard to get a job. Drug tests also make it tough on cannabis users.

    “At home, frequent cannabis use was often tied to physical and emotional abuse of the user’s partner”

    Well, that’s just bullsnot. This whole “study” is classic Reefer Madness trash.

  14. Proudgranny Joan

    March 23, 2016 at 4:53 pm

    im calling a big ole bull shit on this study…. you make it illegal… stigmatize the users
    you jail users and give them convictions that make it hard for them to get good jobs

    then want to say that the big negative effect for users is economic…. well i dont see that cannabis caused the problem… think it was the government had a doing in this one…

    yea… the negative effects of cannabis…. being labeled an economic loser, keep stigmatizing

    notice no health issues are mentioned… because its a natural plant we need to stay healthy

  15. Stel-1776

    March 23, 2016 at 3:58 pm

    There exist many confounding factors for a study such as this:

    -This was heavy use for years under prohibition. For one, prohibition policies can steer some away from better employment for a number of reasons, not only those related to criminal justice.
    -Selecting cases based on having a “dependency diagnosis” presents major selection bias. Maybe the link had more to do with “people who manage to get caught and allow themselves to be labelled dependent”.
    -Psycho-social deficits related to alcohol and tobacco use are being rewritten. Researchers are finding that they are more of a factor than previously thought. Any adjustment for these two confounders, which commonly exist for cannabis consumers, should be taken with a large grain of salt. It is quite possible the effect of them was significantly underestimated.
    -How well was reverse causation examined? People who happen to have lower income tend to use more recreational substances.
    -Many people self-medicate a wide range of health conditions with cannabis, especially heavier consumers. Known or unknown mental or physical health issues can affect employment.

    Potential confounders are endless. As the authors state, “this observational study cannot confirm causation”. This is not to say that cannabis cannot be a vice for some or lead to contentment with one’s life as is, but to say that usage, even regular usage, is particularly harmful is not justified by this study.

    • michael_ellis

      March 24, 2016 at 12:10 pm

      Thanks for this, Stel-1776 and for the good work you’ve been doing in comment sections all over the web, It’s also worth noting that the ‘Dunedin’ study from NZ is suspect for many reasons, not the least of which is that the papers published from this study consistently show worse outcomes than other reputable studies conducted in Europe and the US.

      • Stel-1776

        March 24, 2016 at 4:05 pm

        Thanks. They are a bit suspect. The lead author of this study received funding from the NIDA:

        “M. Cerdá was supported by a grant from the U.S. National Institute
        on Drug Abuse (DA030449)”

        The last major Dunedin study regarding IQ’s (Meier et al. 2012) also partially received funding from the NIDA:

        “US National Institute on Drug Abuse Grant P30 DA023026”

        The NIDA does try to put a negative spin on things, as it is their job.

  16. TheSinnedAngel

    March 23, 2016 at 3:28 pm

    Perhaps they were actually reporting the effects of preferring a harmless PROHIBITED drug.
    Their findings may be skewed by the illegality and not the chemistry.
    Suggestion: legalize it, then study it for another 40 years. Then compare the two studies.
    The Sinned Angel

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