As many dependent on cannabis as have tried heroin?

Feb 24 2010 Published by under Cannabis, Drug Abuse Science

A recent review paper covers animal models of adolescent drug taking, which is in and of itself an interesting read. Human adolescence tends to be a time when people first encounter psychoactive substances taken for recreational purposes. Unsurprisingly, problematic drug taking which emerges later in life often has antecedent roots in adolescent drug taking. The epidemiology goes further in identifying age-graded risk such that the earlier one starts using some drugs, the greater the chances of problematic drug use later in life.
Given the inescapable limitations human epidemiology (lack of random assignment means you cannot eliminate risk-associated variables from the genetic to the environmental) animal models are required to determine if there are neurobiological sensitivities in the adolescent brain which confer increased risk of developing dependence on a given recreational drug. This paper reviews much of the animal studies to date.

Are adolescents more vulnerable to drug addiction than adults? Evidence from animal models. Schramm-Sapyta NL, Walker QD, Caster JM, Levin ED, Kuhn CM. Psychopharmacology (Berl). 2009 Sep;206(1):1-21.

In providing the background context, Schramm-Sapyta et alia did something dear to my heart, as my readers will quickly appreciate. They created an interesting graphical depiction of the conditional probability of dependence on several drugs from the US National Survey on Drug Use and Health (NSDUH, 2007).

SchrammSapty09-Fig1.jpg
Fig. 1 Percentages of the US population over the age of 12 years who have ever tried the indicated drug (top number, light gray circle); who used the indicated drug in the past month (middle number, darker gray circle); who meet criteria for dependence on the indicated drug (bottom number, black circle). Numbers in the center of each diagram represent the percentage of people who have ever tried the indicated substance who are currently dependent. Data obtained from the NSDUH 2007, lifetime use, past month use, DSM-IV dependence criteria (for all drugs except tobacco), and daily cigarette use (for tobacco)

Yes, these are cross-sectional data much like the Anthony et al 1994 paper to which I frequently refer. But these are also large representative sample data so trite dismissals on this basis are hard to support.
What draws my eye? Two things. First, of course, is the number in the center of each set of concentric circles. This represents the percentage of the sample of individuals who have sampled a given drug in their lifetime who are currently dependent. I emphasize "currently" because sometimes you will see data on "ever met dependence criteria"; this latter would result in a higher estimate of dependence risk, obviously. The Anthony et al 1994 data use lifetime rates, not current rates for example. Nevertheless this central number is another estimate of the conditional probability of becoming dependent and more importantly gives us relative relationships for several drugs of interest. [ As always in science, the more replication the better. Slightly different sampling / survey methods will give us different numbers of course. So let us not make the common mistake of viewing every scientific paper in isolation. These numbers need to be integrated with other estimates of conditional probability of dependence that we can find...in a thoughtful way. ]
The second thing that draws my attention can be found in the three numbers listed to the left of the circles. The bottom one represents the rate of dependence in the general population. To my view this is a critical bit of information for those who want to have an informed discussion of public health related policy. The number of citizens affected by a given condition is as assuredly relevant as is the severity of that condition.
These data make it emphatically clear that the number of people in the US who are currently dependent on cannabis slightly exceeds the number who have ever so much as tried heroin. The number dependent on cannabis is three times as large as the number dependent on cocaine and 16 times as large as the number of people dependent on heroin.
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h/t: dr_leigh for passing this along

33 responses so far

  • Dunc says:

    The thing I find interesting is that the two legal drugs on there apparently have the highest probability of dependence... I wonder what the data for caffeine would look like?

  • becca McSnarky says:

    Dunc- the thing that I find uninteresting is that the two drugs that apparently have the highest probability of dependence are the legal ones.
    But yes, I'd love to see caffeine.

  • Mu says:

    What I find interesting in those numbers is how for alcohol, tobacco and marijuana there's a large number of current users not considered dependent, but for cocaine and heroin nearly all users also meet the dependence criteria.

  • Mu says:

    I think price becomes a vital factor, you can be dependent on alcohol and tobacco for $5 a day (and probably even less for caffeine, as long as you stay out of Starbucks). So the average person can support a dependency much easier than the hard core drug addict that has to commit to a life stile centered around obtaining the drug (or the funds for it).

  • El Guerrero del Interfaz says:

    The most surprising data for me it the significative amount of people who use tobacco and are not dependent on it. I say that because I'm one of these and I've never met anyone like me.

  • Kate says:

    I really like this data and will be thinking about it for a while. But, there's a problem- it's 1d data (%s) being represented by 2d circles. Tufte wouldn't like this. Does the radius of the circle represent the data or does the area? Hard to tell. 1d graphs, like lines would be better.

  • whimple says:

    Given the inescapable limitations human epidemiology (lack of random assignment means you cannot eliminate risk-associated variables from the genetic to the environmental) animal models are required to determine if there are neurobiological sensitivities in the adolescent brain which confer increased risk of developing dependence on a given recreational drug.
    I would have phrased this differently. Something along the lines of, "since animal models can never be validated in the human system, animal studies serve as a distraction from actual human studies".

  • Dr. Alcohol Researcher says:

    Becca, really why is that uninteresting to you? Please pontificate.

  • Vicki says:

    If I read the illustration and caption correctly, the study results include that approximately half the Americans who have used tobacco in the past month are not dependent on that drug. Having lived with a tobacco addict (currently not smoking, but relapse is always a risk), and just from looking around and talking to other Americans, I'm startled.
    Ah, I see: "dependent" is a stronger term than "addicted," and includes time spent just on drug use, addiction that interferes with other aspects of life, increased and unintended usage, and unsuccessful attempts to quit. So someone who is physically addicted, but has been smoking the same pack a day for the last five years, and has no trouble taking breaks during which she goes outside and socializes with the other smokers, is not "dependent."
    But if her doctor convinces her that she should quit, and she fails, she now counts as dependent. Or if there's a new law banning smoking in bars and restaurants, so she now has to choose between hanging out with her friends there or standing outside in the cold with a cigarette, she's more likely to be considered dependent. Even increased cigarette taxes could make someone more likely to count as dependent, despite no change in their behavior.
    I don't think this is necessarily an unreasonable definition--drug dependence is a social phenomenon--but it's not most people's idea of the words. And without context, people might read this as suggesting that alcohol and tobacco aren't that bad--precisely because they are legal and somewhat acceptable. But if we turn it around and say "We could reduce heroin addiction by legalizing possession and not drug-testing job applicants," there'd be a lot more objection.

  • dt says:

    I think that cannabis's popularity makes it less deserving of illegality. But even if you think the opposite, DrugMonkey, we live in a democracy, and popularity makes it less likely to remain illegal.

  • DrugMonkey says:

    The most surprising data for me it the significative amount of people who use tobacco and are not dependent on it.
    I was surprised by this realization as well...
    http://drugmonkey.wordpress.com/2007/04/26/drugs-are-bad-mkay/
    Vicki-
    Yes. There is a lot of variety in what people perceive as drug addiction, drug dependence, a drug "problem", etc. The idea of having somewhat consistent diagnostic criteria is a good one but should never be understood to be the final word for anything. In particular if you see the different ways one can qualify for dependence under a given set of criteria, two drugs may produce the same diagnosis by very different means. The current DSM-IV criteria are very clearly contaminated by the legal status / social acceptability of the drug in question. (as an aside, this same incongruity inre social acceptability keeps people with middling to strong levels of religious belief from being diagnosed with a psychosis)
    But to assert a strong prediction on which way things would go if nicotine were criminalized or cocaine legalized is a tricky business. Would pot become as popular as alcohol? as cigarettes? no change? we really don't know until the experiment is done for a given population/culture. (and yes, we've dealt with the Portugal thing, it remains to be explained why they had such low rates of pot use in the first place)

  • queenrandom says:

    Some of the confusion re. tobacco use might come from this definition: "The National Survey on Drug Use and Health (NSDUH) includes a series of questions about the use of tobacco products, including cigarettes, chewing tobacco, snuff, cigars, and pipe tobacco." If we are assuming tobacco = cigarettes, then we are making a mistaken assumption.
    I'm not an expert on what's in different tobacco products or how much addictive substance gets into your blodstream when its used, but I do know that it varies a lot. For example, by definition, a person who smoked a cigarette and a person who smoked a cigar in the last week would be in the dark grey circle; but are cigar users more casual/social users than cigarette users (I find this to be true, however I could be wrong; additionally, you fully inhale cigarette smoke however to smoke a cigar properly, you simply let it waft in your mouth - this is a difference in delivery)? Perhaps there is a higher percentage of cigarette users in the black circle than of cigar users. I'd be interested in seeing a breakdown of the tobacco target chart by type of tobacco used, even if in some ways it's beside the point :)

  • Isabel says:

    What I find interesting is how many lawbreakers there are out there. 40% of people over age 12? Shocking!

  • penny says:

    DrugMonkey - But to assert a strong prediction on which way things would go if nicotine were criminalized or cocaine legalized is a tricky business. Would pot become as popular as alcohol? as cigarettes? no change? we really don't know until the experiment is done for a given population/culture. (and yes, we've dealt with the Portugal thing, it remains to be explained why they had such low rates of pot use in the first place)
    Cannabis has been legally and openly sold in Holland to anybody over the age of 18 for 30 years. The science and proof is there, in reality, cannabis is far less harmful and addictive than all other drugs, legal or not (and most foods!).

  • becca says:

    Dr. Alcohol Researcher- I was speaking ironically.
    Although, thinking about the situation in more depth, I know I must have been wrong- or at least not paying enough attention. After all, I was assuming high likelihood of dependency -> more public support for a drug (if you're dependent on it, it's harder to vote to get rid of it). Yet if that's the case, to apply it to this situation, we also have to assume that when there's more public support for a drug -> the drug is legal. Which would make sense. In a democracy of rational actors. HAHAHAHAHAHHAHAHA*
    *(I live in Pennsylvania and the alcohol laws around here aren't decided by consensus. Actually, I'm pretty sure they're made by a weird amalgamation of historical agendas and dart boards, with possibly some tarot card readings thrown in.)

  • SurgPA says:

    As long as we're throwing out "I think it's interesting that..." Am I reading this correctly that the percentage of ever-tried-it who are currently dependent is the same for marijuana and cocaine (4%)? That's not what the DARE counselors were saying "back in the day."
    #18 "The science and proof is there..." What science and proof? That marijuana is legal in Holland? I don't think that's in dispute. Do you have any actual data you'd like to share about usage and dependency patterns in Holland?

  • SurgPA says:

    Sorry, I meant to direct my last comment at Penny in #14.

  • DrugMonkey says:

    hmm, so according to that
    1) Cannabis is still a controlled substance in Netherlands and always has been
    2) they have a policy of tolerance for consumption, not for production
    3) many municipalities in the Netherlands are rolling back their tolerance
    4) cross sectional data show use rates in the Netherlands that are lower than in the US
    ...lot more questions than answers posed by the Netherlands experience.

  • Adi says:

    As usual, I'm impressed with the background and comprehensiveness of this post. Having switched the measurment from lifetime- to current-dependence has left me with quite a few things to ponder - Firstly, the good old 10%-15% approximation i've been using just got tossed out the window (as far as others are no doubt concerned), though I would imagine another important measure here would be "% of those who are currently using who meet criteria for dependence." I wonder what that one would look like...
    Also, I like seeing that at least when it comes to illicit substances (yes, even MJ), the ever versus 30day prevalence ratio is substantially lower than for llicit drugs.

  • qbsmd says:

    I really like this data and will be thinking about it for a while. But, there's a problem- it's 1d data (%s) being represented by 2d circles. Tufte wouldn't like this. Does the radius of the circle represent the data or does the area? Hard to tell. 1d graphs, like lines would be better.
    Posted by: Kate

    They're Venn Diagrams, a pretty standard way to depict probabilities. The the numbers listed depict the relative areas. I would guess that it's easier for a human brain to process data that way than numbers or 1 dimensional information.

  • Rogue Medic says:

    @13 Isabel,

    What I find interesting is how many lawbreakers there are out there. 40% of people over age 12? Shocking!

    Is that meant to be silly, or are you really unaware that a large percentage of the population will disregard laws imposed on them using the excuse that it is for their own good. The real reason for these laws is that these vices are not vices that are politically correct.

  • rijkswaanvijand says:

    @19
    3 simply isn't true.. our central government (mostly christian extremists) indeed want to roll back on this tolerance, while most municipalities actually support legalization.

  • DrugMonkey says:

    I didn't say "most". And the news accounts don't say "central government" they mention more local city authorities. Happy to get a fuller picture though...Do you have any sources for number of sales points in the Netherlands across time? It would be nice to see if there was a general expansion/ retraction / stability

  • Lee M Farmer, MD says:

    Drugmonkey: can you answer the question posed by the article "Are adolescents more vulnerable to drug addiction than adults? Evidence from animal models." As a parent I'd like to know. I'm frustrated by Cheech and Chong making a national media circuit promoting their "get it legal" comedy tour and getting serious air time. My ex wife became addicted to drugs and it devastated our lives. It began with Marijuana.

  • Rogue Medic says:

    I still wonder why marijuana is considered a gateway drug. If you spend any time around people in rehab, the overwhelming drug they seem to use is tobacco.
    It would be interesting if this study had looked at the percentage of current addicts and the percentage of all addicts (for each drug) and what other drugs they had used prior to first using that drug. I would expect that the answer would be marijuana significantly less often than cigarettes.
    I would also expect that for marijuana addicts, cigarette use came first for significantly more marijuana addicts, than marijuana did for cigarette addicts. Even after factoring for any difference in legality and availability.

  • DrugMonkey says:

    @25- not easily or quickly, no. As the review concludes in a very general sense, the adolescent brain appears tipped toward finding drugs more rewarding and less aversive compared with adults. adolescents also appear less sensitive to withdrawal effects. as I mention now and again it is still a debate in the research as to what is most important in addiction. ultimately it comes down to *which stage of addiction* one is worried about. the potential to start down that road? or the potential to actually progress to the point of no-return?
    @26- I don't think the scientific evidence supports any specific gateway role for cannabis, speaking neurobiologically. Nor, for that matter, a specific role for any drug. There are simply too many sociological/environmental factors which offer better explanatory value, in my view. Nevertheless, sociological and environmental factors are *real*, when it comes to causing behavioral change. Very real.
    It is unfortunate, imo, that PR campaigns (on both sides) gloss over the way "gateway" is used.

  • Passerby says:

    Addiction just doesn't just 'rewire' cellular response to a substance, long-term use alters brain center structures involved in emotional and risk perception and behavioral controls - permanently, it appears. This begs the question of what these substances do to life-stage dependent gene and protein expression regulation.
    Aren't there collateral costs for addition to one substance, as both chemical effect and social practices that go with use of one substance may reinforce exposure, use, abuse and co-addition to other substances?
    With changes in brain chemistry and micro-structure, comes changes that affect overall mental and physical health: altered sleep quality and immune system response, malnutrition, sedentary lifestyle, poor stress tolerance, risk-tolerant aberrant social/interpersonal behaviors.
    These also affect addiction susceptibility and addiction-related cellular damage.
    Mexican heroin, skunk and even cigarettes are all examples of addictive substances that are widely available in far more potent and dangerous modern versions, with respect to 'parent' product in use decades ago.
    Cigarette tobacco and filters have been engineered to deliver higher doses of nicotine and smoke micro-particulates deep into lungs. where uptake is more effective and damage more pervasive. Nicotine junkies unable to give up smoking and who practice self-deception of 'just a few puffs' during a smoking break, are inhaling nearly the equivalent dose of nicotine in those few puffs to smoking an entire cigarette produced in the early 90s.
    Marijuana crops have been selected to enhance drug gene expression, to produce a product ('skunk') to meet meth-user demand for a 'bridging' drug highs between meth use sessions. This has substantially boosted skunk availability through a booming drug-trafficking distribution system in the US and Canada, Europe and the UK and throughout Asia and the South Pacific.
    Lastly, addiction and aberrant risk recognition and behavioral controls may increase pathogen infection susceptibility, where changes in immune system function and social behaviors increase exposure risk. A direct risk example is the recent report of pathogens found in tobacco that are capable of surviving combustion to be transported into lower respiratory tract. An indirect risk example would be risky behaviors during intercourse (oral-anal exposure route) and impaired immune function that increases infectious agent exposure and infection probability at lower dose.
    I wish that graphic had included amphetamine and 'study aid' drugs.
    Here is why I suspect that children and adolescents are highly susceptible to substance addiction: they are inherently less capable of dealing with social stress of dynamic peer- and self-identity development, than adults who have mastered role responsibility and adapted social stress coping behaviors. Secondly, adolescents experience peak loads of physical (metabolic) stressors during rapid bouts of physical growth.
    'Reward' seeking behavior is a response to stress. This life-stage has very high expression of ROS-scavenging systems, for dashed good reasons.

  • Joao Menezes says:

    There is a problem in using the % of all of those that tried and are now dependent. Because Heroin addicts die faster, the actual number of dependents are smaller then the ones that would be considered dependent if alive. The same may be true to tobacco. The in case of marijuana which does not kill directly the effect may be less.
    The other problem is defining dependency for marijuana. Most studies use subjective criteria for this definition, since there is no clear cut objective tell tale sign for dependency (tremors, increased heart rate, vomiting, sweating) studies are mostly bias (the investigators had to create the nosological criteria). So it doesn't matter how robust you claim the cross sectional study was, the definition does matter, and yes the results can be dismissed at least for marijuana.
    So both these observations reduces the validity of your final conclusion. If heroin addicts did live longer this percentage would be hgher. Second what if dependency of pot is overestimated since people usually lie when questioned if ever tried and in contrast usuallyseek treatment against their will!

  • Is that meant to be silly, or are you really unaware that a large percentage of the population will disregard laws imposed on them using the excuse that it is for their own good. The real reason for these laws is that these vices are not vices that are politically correct.

  • [...] You will recall from my posts trying to work out the conditional probability of dependence, that I am not a fan of simple, drug-feels-good models of drug reinforcement; even though they have [...]

  • drugmonkey says:

    And another good thread for the new readers...

  • [...] why is this interesting? Well, as we've covered in the past the notion of conditional probability of dependence is a key issue for parents and policy makers and yet we have really poor estimates on that. Direct [...]

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