The Dose Makes the Poison, Even for Marijuana Smoke

In a recent study published by the journal Chemical Research in Toxicology, Health Canada researchers found higher levels of certain toxins in marijuana smoke than in tobacco smoke. The researchers used a smoking machine to compare cigarettes made from Players brand fine-cut tobacco with cigarettes made from cannabis produced by Prairie Plant Systems of Saskatoon, which grows medical marijuana under contract with Health Canada. The marijuana smoke had 20 times as much ammonia and five times as much hydrogen cyanide and nitrogen oxides, possibly due to higher levels of nitrate fertilizer traces in the marijuana. Then again, only the tobacco smoke contained the potent carcinogens known as tobacco-specific nitrosamines, and it had "moderately higher levels" of potentially hazardous compounds such as formaldehyde, acetaldehyde, and polycyclic aromatic hydrocarbons. Guess which comparison was emphasized in the press coverage.

"Cannabis smoke 'has more toxins,'" BBC News reported, warning that ammonia is "linked to cancer," while hydrogen cyanide and nitrogen oxides "are linked to heart and lung damage respectively." The Guardian agreed: "Cannabis smoke more toxic than puffing tobacco." Even EarthTimes ("Cannabis smoke more harmful than tobacco smoke") and New Scientist ("Inhaled cannabis is more toxic than tobacco smoke") went along with this gloss. But it's not what the researchers reported (emphasis added):

The combustion of any plant material will result in a complex mixture of chemicals, the composition and percentages of which depend on a large number of variables. The present study supports previous research and found that marijuana smoke contains qualitatively many of the same chemicals as tobacco smoke. This qualitative similarity is more important when assessing the risks for adverse outcomes than are the differences in level of a particular substance, which can change from sample to sample or from one smoking condition to another.

Even more important in assessing the health risks of pot smoking is a point that BBC News halfway acknowledged: While a joint a day would count as fairly heavy consumption for a pot smoker (since most pot smokers light up occasionally), the current mean for cigarette smokers is about 14 cigarettes a day (down from about 20 in 1993). This huge difference in dose is presumably the main reason pot smoking has not been linked to cancer, heart disease, or emphysema in epidemiological studies, despite the similarity between marijuana and tobacco smoke. Those still concerned about possible respiratory effects, of course, can avoid combustion products by using vaporizers (as do many patients who use marijuana as a medicine).

Addendum: A commenter asked about the efficacy of water pipes in reducing the hazards of pot smoking. They do not work nearly as well as vaporizers, partly because they filter out THC, encouraging people to smoke more for the same effect. Here is a report on research comparing water pipes to vaporizers, which says, "We learned early on that waterpipes don't help filter out undesirable particulate matter, although waterpipes may help reduce certain water-soluble gases."

Editor's Note: We invite comments and request that they be civil and on-topic. We do not moderate or assume any responsibility for comments, which are owned by the readers who post them. Comments do not represent the views of Reason.com or Reason Foundation. We reserve the right to delete any comment for any reason at any time. Report abuses.

  • the troll in edward\'s brain||

    hydrogen cyanide can be produced by zyklon B.

    zyklon B was used by the Nazis to kill Jews

    Ron Paul wants to legalize marijuana usage

    marijuana smoke has 5X as much hydrogen cyanide as tobacco smoke

    therefore, Ron Paul is an anti-semitic, pothead Nazi

  • ||

    This huge difference in dose is presumably the main reason pot smoking has not been linked to cancer, heart disease, or emphysema in epidemiological studies, despite the similarity between marijuana and tobacco smoke.

    Wait till I tell my nanny (gov't at all levels) that exposure matters. Who knows, maybe we can get cyclamates* back on the market.

    *the first irrational nanny intrusion into my life that I specifically recall.

  • ||

    Just one puff of second hand marijuana smoke will give you the heart disease factor of Rush Limbaugh.

  • ||

    Those still concerned about possible respiratory effects, of course, can avoid combustion products by using vaporizers (as do many patients who use marijuana as a medicine).

    Except that many states have banned vaporizers as paraphernalia, thus making illegal the safest way to ingest a controllable dose of cannabis/THC. THANKS DEA!

  • ||

    I was the kid in my high school health class who, after being told that marijuana has 5 times the carcinogens of tobacco smoke, raised my hand and asked "does anyone here know of anyone who smokes a pack of joints a day?" The teacher was pretty cool too so all she did was ignore my point instead of sending me to the principal's office or something that other teachers might do.

  • Kolohe||

    The teacher was pretty cool too so all she did was ignore my point instead of sending me to the principal's office or something that other teachers might do.

    You mess with the moose, you get the antlers?

  • Kolohe||

    Most of the research is rather silly anyway. Of course combustion of any organic material has harmful byproducts. Even friggin cavemen understood pretty damn quickly that it is preferable to sit upwind of a campfire than downwind.

  • ||

    Potheads: how much of the bad stuff gets taken out of the smoke when you use a bong?

  • ||

    You mess with the moose, you get the antlers?

    Oh, I don't think anyone would have classified me that way. I'm more of a peaceful type.

    I was just speculating that a lesser teacher may have gotten offended by my less polite way of making a point that many would rather not be made because it could be seen as encourraging the use of marijana, which of course is a horrible, horrible thing.

  • ||

    I almost tried pot shortly after my arrival at college, but my room mate took the first toke and immediately dropped dead. Then, he became a communist.

    That's my story, and I'm sticking to it.

  • ||

    the current mean for cigarette smokers is about 14 cigarettes a day (down from about 20 in 1993)

    The smokers I know smoke a lot more than 14 cigarettes a day.
    They also smoke pot so I guess they're gettin the double whammy.

  • ||

    The smokers I know smoke a lot more than 14 cigarettes a day.

    I smoke 6-8 cigarettes a day. Too much, yeah. I'm hardly alone in that consumption range.

  • Brandybuck||

    Those of you out there who think progressvies want to legalize pot are ignorant. Yes, ignorant. You know who you are. Because of this study they'll keep pot illegal because it's bad for you. They banned trans-fats, thinking about banning sugary sodas, what makes you think they'll go easy on marijuana? As long as they can maintain a personal stash, they could care less about your freedoms.

    The defender of your liberties rests with people who understand what liberty is. And that excludes anyone who wants to order society or manage behavior.

  • I RESENT BEING CALLED A POTHEA||

    Warty | December 19, 2007, 12:53pm | #

    how much of the bad stuff gets taken out of the smoke when you use a bong?


    well... it reduces a lot of the larger particulate matter (flaming embers, unburned material) that you'd often inhale via a pipe for instance... which can be easier on the lungs. Less loose crap left in your lungs. But as far as the chemical composition of the smoke itself, I think it's largely the same. Also, hitting a bong usually means trying to fill your lungs completely, the equivalent of smoking a whole bowl in one go, basically, so the net effect can be a lot more impactful than taking a few puffs. Probably not 'healthier' overall when you take that into account (dose again).

    people who are keen on vaporizers are kinda lame IMO. Just skin one up and dont be such a wuss. 20+yrs of pot smoking hasnt had much effect on the half dozen people I know who still light up daily.

    There should be a "Gary Katz Death Watch" or something... the producer for Steely Dan, guy who first signed Prince, others... A friend of mine interned in his studio, and i visited once, and this guy indeed DID smoke a pack of joints in a day. He rolled them at night and kept them in an old cigarette case. He ripped through them like nothing. I thought he was going to 'be cool' and offer me some. Nope. Dude was on another level. He had no stereotypical features of the 'stoner'. He was an uptight neurotic workaholic micromanager. In fact, a lot of the people I know who are heavy users are more "hyper" types than hippies. Maybe it oils the gears, who knows.

  • ||

    Not only don't people smoke pot as often as cigarettes, they don't smoke nearly as much. 'One hit' pot is much more available now than in decades past. Likewise, the market for 'ditch weed' is all but nonexistent at any price. What passes for a "fatty" today wouldn't have even been worth rolling years ago. Naturally the drug warriors find this very alarming.

  • ||

    I'm sorry to keep doing this, but given the thread topic, I'm going to have to plug this movie again
    Reefer Madness

    and here's a synopsis of it that I found:
    This film tells the tale of the Harper Affair, in which young Jimmy Harper finds his life of promise turn into a life of debauchery and murder thanks to the new drug menace marijuana. Along the way he receives help from his girlfriend Mary and Jesus himself, but always finds himself in the arms of the Reefer Man and the rest of the denizens of the Reefer Den

    It's an instant classic!

  • ||

    Even friggin cavemen understood pretty damn quickly that it is preferable to sit upwind of a campfire than downwind.


    Dec 19, 21,000 BC

    Ouagha, High on the Mountain Cave Tribal Health Enforcement Officer, today issued an order banning fires while children are in the cave. All cooking will now have to be done outdoors.



    Dec 19, 20,999 BC

    Tharg, Chief of the Tribe from the Other Side of the Mountain, officially declared the High on the Mountain Cave vacant and announced that a new sept of the Tribe from the Other Side of the Mountain would be established there. "Is good cave." He said. "With nice place for fires inside to keep from freeze to death when cold time come."

  • Alice Bowie||

    Keep Dope Alive !!!

  • ||

    Re:Bongs
    I think the main health advantage in a water pipe is in reducing the temperature of the smoke. I remember reading back in the 80's that this was significant in reducing the risk of cancer and respiratory disease.

  • ||

    I keep hearing how much more evil modern marijuana is 'cause it has more THC in it. But in light of this, that is a health feature, not a bug, if indeed it is even true.

  • Tracker||

    I want to see a study that evaluates the dangers of smoke inhaled at the church barbecue.

  • ||

    Here is a report on research comparing water pipes to vaporizers, which says, "We learned early on that waterpipes don't help filter out undesirable particulate matter, although waterpipes may help reduce certain water-soluble gases."

    This sounds dubious. I think I am going to have to bust out the bong and do lots more research on the subject.

  • ||

    "The marijuana smoke had 20 times as much ammonia and five times as much hydrogen cyanide and nitrogen oxides, possibly due to higher levels of nitrate fertilizer traces in the marijuana. "

    Now here is a good argument for organic farming.

  • ||

    I think that anyone who is interested in any recent study on marijuana should read the recent
    article released by Carrie Leigh's Nude Magazine.
    Their investigation takes into account all studies administrated and the subsequent political outcome of these studies.
    Their reporters also demonstrate that to take one study on its merit is insignificant.

  • Paul||

    While a joint a day would count as fairly heavy consumption for a pot smoker

    Hmm...

    I smoke two joints in the morning, I smoke two joints at night
    I smoke two joints in the afternoon, it makes me feel alright
    I smoke two joints in time of peace, and two in time of war
    I smoke two joints before I smoke two joints, and then I smoke two more

  • ||

    I vaporize 0.2 grams of quality cannabis each night before I go to bed. It helps me to deal with a sleep disorder far more effectively (and far less expensively) than any prescription medication my neurologist ever prescribed. At that rate it would take me almost five months to use up the amount of marijuana equivalent to amount of tobacco in one pack of cigarettes.

    Do I worry about toxicity? NO! First of all, the quantity I use is minimal. Second, I use a vaporizer. All of the toxic chemicals mentioned are products of incomplete combustion. No combustion = no toxicity.

    A lot of the problems with marijuana cited in this report have to do with the source of the marijuana used in the study, not with traits of the plant itself. A tiny percentage of medicinal marijuana users in Canada use the "official", government-approved marijuana produced by Prairie Systems. It lacks in potency, tastes like crap, and is very harsh to smoke. Quality marijuana doesn't contain nitrogen and other fertilizer residues. Growers leach out the fertilizers by not feeding the plants for as much as two weeks before harvesting and flushing them repeatedly with fresh water.

  • ||

    Another difference between marijuana and cigarette smoke is the various cannabinoids (THC and many others) present in marijuana, but absent in tobacco. Many of these cannabinoids have been shown to actually oppose cancer growth. I think these cannabinoids give marijuana a protective quality that tobacco smoke lacks, and this explains why smoking marijuana has NEVER been associated with lung cancer (once cigarette smoking is controlled for). In fact, the most comprehensive study I'm aware of (out of UCLA in 2005 I think) suggested that smoking marijuana actually decreases the lung cancer risk of cigarette smokers.

  • Lavinia Weissman||

    Funny, yesterday in the little town of Langley WA on Whidbey Island, I witnessed teenage young men interviewing younger men about how they treat young teens on a date and if they do drugs.

    I was in shock to think that a 15 years old teen was telling younger kids to stop doing drugs.

    When I talked with this kid further, I found out he had just got off probation but stopped his onw participation in N/A.

    He said he was going to continue to smoke marijane.

    My real question is this:


    "When will we own anything we put in the air?" and teach that to our kids?

  • ||

    I'm sorry to keep doing this, but given the thread topic, I'm going to have to plug this movie again Reefer Madness

    In the '70s I owned a tanktop that had a Reefer Madness poster imprinted on it. two lines from that shirt/poster I still remember,

    They took a drag of concentrated sin!
    Weed from the Devil's garden!

  • Paul||

    Do I worry about toxicity? NO! First of all, the quantity I use is minimal. Second, I use a vaporizer. All of the toxic chemicals mentioned are products of incomplete combustion.

    Buzzby, forgive the trollish post but, erh, in this new-fangled super-safe environment we live in, doesn't someone, somewhere have to prove that the product "isn't dangerous" before we declare it safe?

  • ||

    5,000 years of documented human use without any deaths is the best proof of safety one could hope for. Even aspirin is responsible for ~10,000 deaths per year.

  • ||

    Buzzby-

    .. interesting to hear from someone else who uses cannibis for a sleep disorder .. I, too, have a bad case of insomnia I've used pot in the past and it worked well..

    .. because of job considerations I had to give it up .. my MD is trying me on Marinol and it working moderately well

    .. Hobbit

  • ||

    I thought I recognized the named sources of the cannabis, GEEWHIZ wonder why the tests were so dismal?

    http://www.safeaccess.ca/pr/csapr8.htm

    "Oct.1, 2003: Despite an independent test by Canadians for Safe Access (www.safeacess.ca) indicating elevated levels of heavy metals such as arsenic and lead [i] on the Health Canada cannabis being cultivated in an abandoned copper and zinc mine in Flin Flon Manitoba by Prairie Plant Systems (PPS), neither Health Canada nor PPS has acted to reassure Canadians that this product is indeed safe.

    When repeated calls to PPS went unreturned, CSA conducted research to assess the possible cause of such heavy metal contamination. We were shocked to learn that due to the extensive mining and smelting that has taken place in the region over the last 80 years, Flin Flon is considered one of the most contaminated regions of Canada. According to Carol Ptacek, a researcher with Environment Canada's National Water Resource Institute, water near an abandoned mine located outside of Flin Flon Manitoba has some of the highest levels of metal contamination in Canada, if not the world."

  • weedy||

    They of course fail to mention that if weed was legal, everyone would have access to hash and hash oil. I would love to see them compare cigarettes to hash oil.

  • Alastair||

    Why don't these studies analyze the amount of toxins actually entering the mucosa and the rest of the body? This is a critical test since it is known that cannabis is an expectorant - how much of the toxin is repelled and excreted by mucus/expectorating cannabis smoke v tobacco smoke?

    Unless such tests are done all the associations and causations implied by most reporting are simply conjecture. Scientists (me) don't set out to create such conjecture though. Its the f. nazi media that consistently compiles small and often meaningless steps in scientific knowledge into some kind of conclusion that suits their twisted sense of reality.

    But when 'discussing' cannabis the media seems to go past twisted reality into full-blown schizophrenia - and they don't toke! Reckon that.

  • dhex||

    In fact, a lot of the people I know who are heavy users are more "hyper" types than hippies.

    i've noticed this as well, especially in the music industry. my theory is that they get used to working in a state of absorbed fixation, which eats their manners alive. (among other issues)

  • Guy Montag||

    the current mean for cigarette smokers is about 14 cigarettes a day (down from about 20 in 1993)

    Those folks just aren't trying. I can go through 14 before I am done with an "oil can" of Fosters.

    Nothing here about that "tar" in weed being worse than that in tobacco? I was hearing that one for ages but don't see anything on it lately.

  • Chris Bennett||

    This whole test is a fiasco, they used Prairie Plant Systems grown cannabis, and many of the contanimants reported are from the cannabis being grown in a mineshaft.

    Health Canada's Dirty Little Secret - Flin Flon Area Contamination

    Canadians for Safe Access Press Release:
    Received on October 1, 2003 from CSA representative - Philippe Lucas

    Government "Medicinal" Marijuana Grow-Op Located
    In One Of Canada's Most Contaminated Regions

    Canadians for Safe Access - Press Release: October 1, 2003

    Despite an independent test by Canadians for Safe Access indicating elevated levels of heavy metals such as arsenic and lead on the Health Canada cannabis being cultivated in an abandoned copper and zinc mine in Flin Flon Manitoba by Prairie Plant Systems (PPS), neither Health Canada nor PPS has acted to reassure Canadians that this product is indeed safe.

    When repeated calls to PPS went unreturned, CSA conducted research to assess the possible cause of such heavy metal contamination. We were shocked to learn that due to the extensive mining and smelting that has taken place in the region over the last 80 years, Flin Flon is considered one of the most contaminated regions of Canada.

    According to Carol Ptacek, a researcher with Environment Canada's National Water Resource Institute, water near an abandoned mine located outside of Flin Flon Manitoba has some of the highest levels of metal contamination in Canada, if not the world. "It's like battery acid, basically -- maybe not quite as strong", stated Ptacek.

    Furthermore, elevated levels of arsenic, lead, cadmium, and copper have long been detected in soil up to 75 kms from the site of the former smelter.

    According to MineWatch Canada, "the sheer size of the contaminated area in Flin Flon makes it impossible to remediate. In particular, there is a large volume of tailings that blow in the wind, and the metal content (copper, cadmium and lead) makes it difficult for vegetation to establish. Community concerns have historically not been adequately addressed, and much information, including that collected by Health Canada (e. g., toxic metal levels in blueberries) has not been made available to the residents of Flin Flon."

    And from a Manitoba Conservation report: "Air pollution at Flin Flon near Hudson Bay Mining and Smelting continues to exceed provincial air quality objectives, with no noticeable changes from previous patterns… Records also show that, in Flin Flon, levels of particulates, and concentrations of lead and arsenic, sometimes exceed provincial objectives and guidelines."

    A past interview conducted with PPS President Brent Zettl indicates that the water source used by PPS is drawn from a nearby lake, and that the growing medium for the cannabis is enriched local outdoor soil. If this is the case, this could well be the source of the reported contamination.

    Philippe Lucas, Director of Canadians for Safe Access and a legal user of therapeutic cannabis, feels that Canadians deserve immediate answers to the following four questions:
    Was Health Canada aware that it was cultivating medicine in one of Canada's most contaminated regions?
    Has PPS carried out regular heavy metal and radon testing of its product, soil and water throughout the 3+ years that it has been growing cannabis in this mine?
    If these tests were conducted, have they ever indicated elevated levels of heavy metals or radon?
    In light of CSA testing and the fact that at least two legal recipients of this product have stated that it made them physically ill and actually sent the product back to Health Canada, when will Minister McLellan and Prairie Plant Systems begin to take seriously the very real concerns of Canada's critically and chronically ill, who are to be the end users of this product?

    CSA believes that Health Canada could have saved millions of dollars and years of unnecessary work and suffering had they shown the common sense to listen to the concerns of experienced users, cultivators and distributors, who have expressed worries over possible heavy metal contamination and have stressed the importance of organic cultivation since it was first announced that this product would be grown in an abandoned Copper and Zinc mine.

    "Canada's compassion clubs and societies have the experience and expertise that is so obviously missing from the Office of Cannabis Medical Access", says Lucas, "they are currently the only safe source of cannabis for Canadians suffering from critical or chronic conditions, and they are contributing more research than any other organization, including Health Canada; all at no cost to the taxpayer."

    "If the federal government has a better model, Canadians have yet to see it."

    Canadians for Safe Access advises Health Canada to cease the distribution of Prairie Plant Systems' cannabis to legal users and researchers until the extent and results of their safety testing is revealed, and accommodations are made for an independent analysis of this product.

    For more information on heavy metal contamination in Flin Flon, please see:
    http://safeaccess.ca/research/flinflon.htm
    or see below research data and associated source links.

  • ||

    We must put this in perspective.
    yes we know smoking has it's bad toxins.
    However we also know it would take massive amounts of pot use to cause any real damage over a very long time.I've used pot for 38 years and smoked cigs 2 packs a day for 25 years- i think the THC protective elements in the pot smoke has helped me stay healthy.
    Used in moderation -I'd say it's no more dangerous than an afternoon walk on a sidewalk on a sunny day.

  • Neu Mejican||

    "does anyone here know of anyone who smokes a pack of joints a day?"

    9th grade Neu Mejican raises hand...giggles...[duuuude how'd yuh know?...wait, what?]

  • Cheese||

    buzzby's a pothead so of course he's going to be pro cannabis.

    prepare for a lot of people digging as deep as they can to try and prove this article wrong and some all out blatant denial

    this is old news and obvious. Smoking anything is bad for you.

    who really didn't know this already? That ALL organic materials when combusted produce harmful by products and carcinogens?

  • X||

    Stephen John-Don't be so foolish and ignorant. Smoking anything isn't good for your body.

  • JT Barrie||

    Why hasn't someone promoted use of vaporizers for nicotine addicts? Would the use of vaporizers reduce the risks of lung problems for these addicts? Or is this a result of "zero tolerance" for tobacco - suggesting that cigarettes are next on the ban list?

  • BeadWired||

    QUOTE FROM Canadians for Safe Access - Press Release: October 1, 2003

    "According to Carol Ptacek, a researcher with Environment Canada's National Water Resource Institute, water near an abandoned mine located outside of Flin Flon Manitoba has some of the highest levels of metal contamination in Canada, if not the world. "It's like battery acid, basically -- maybe not quite as strong", stated Ptacek."

    Thanks Chris Bennett for that article... it makes sense why the cannabis in the mine could be toxic... there are 2 agendas in this war on cannabis... the ones who think marijuana is a poisson & the ones who think marijuana is a herbal medicine. i hope someday, people will see the light & the truth about marijuana as a medicine...

    lighten people and show compassion to those who use marijuana...

    go visit: www.christiansforcannabis.com
    or visit: www.medicalmarijuanainformation.com

  • X||

    Everyone knows that the real idea behind medical marijuana isn't to help sick and dying people but it's just to get high!

GET REASON MAGAZINE

Get Reason's print or digital edition before it’s posted online

  • Video Game Nation: How gaming is making America freer – and more fun.
  • Matt Welch: How the left turned against free speech.
  • Nothing Left to Cut? Congress can’t live within their means.
  • And much more.

SUBSCRIBE

advertisement