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This picture is from Emily Miller's Facebook page shows one lung divided into two parts one labeled Tobacco and one labeled Marijuana. The Marijuana side is substantially less-healthy looking and the the picture's caption reads,

Marijuana deposits four times more tar in the lungs than tobacco

Picture of lungs

You can find the post here (dated Feb 5, 2013), Emily comments on it,

Obama hails CVS for stopping selling tobacco products but has no trouble with smoking marijuana. This photo from

I was able to find Drug Free America Foundation's original post of the picture here (also dated Feb 5).

Sklivvz
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Evan Carroll
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    You can always just eat it, no tar in brownies, only chocolate. – SIMEL Jul 29 '14 at 21:12
  • Right. 4x the tar does not, by any mean, mean 4x as cancerous, or as bad. It does not me 1 joint = 4 cigs. Tobacco contains nicotine, and marijuana doesn't. Nicotine hardens the arteries and may be responsible for much of the heart disease caused by tobacco. Marijuana contains THC. THC is a bronchial dilator, which means it works like a cough drop and opens up your lungs, which aids clearance of smoke and dirt. Nicotine does just the opposite. Marijuana offers so much and has little negatives making it a clear cut winner over tobacco. –  Sep 06 '14 at 03:59
  • Yes. But that's less dependent on what you smoke, and more on how you smoke. Marijuana smokers smoke blunts and mostly in social gatherings, hence more SMOKE (nothing to do with THC, which is the active ingredient). I won't iterate what many people have already said in their answers. But, to add to the discussion, I have 2 points. 1. A more definitive result to this question would be the study of the effect of both using a vaporizer. 2. A more useful comparison would be "Tobacco gives cancer, while Marijuana doesn't". – Hec Oct 07 '14 at 22:41

3 Answers3

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Yes, it does, approximately 3 times that amount by weight, but that's not the whole story. You should consider other factors too in determining whether this means it is more harmful:

Firstly, when people smoke cannabis leaves or buds, they smoke them in a rolled cigarette which is usually larger than a tobacco cigarette. This would suggest that not only does cannabis smoke contain more tar, but that cannabis users inhale more smoke. In the outset, this seems worse.

Consider also, however, that cannabis smoking is often a social activity, and that people may not actually smoke much of a joint to themselves in the main. It may also be the case that cannabis smokers may not smoke as often as cigarette smokers. Both of these facts may suggest that cannabis users don't typically inhale as much tar overall, as actual amount of smoke inhaled could well be 1/3rd or less of the smoke inhalation of a regular smoker.

Equally, a portion of cannabis smokers will also smoke tobacco.

In considering the content of tar, you may also consider that low-tar cigarettes haven't be shown to actually reduce risk of cancer, and hasn't been shown to reduce emphysema either.

The basic conclusion of this is that yes, we know that cannabis smoke contains more tar, but we don't know that that makes it more harmful, nor do we know whether cannabis users actually inhale more tar, even though cannabis contains more. The answer to your question is yes, but whether or not the difference in tar content impacts health is undetermined.

Owen C. Jones
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    Good answer to the question, followed by a lot of un-referenced, and only tangentially-related claims. – Flimzy Feb 19 '14 at 01:13
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    Just intended to be a primer for further enquiry - you'll notice that the majority of what follows is prefaced by "may" or "might". I was keen to avoid a reader of the answer assuming an false syllogism that cannabis is necessarily more harmful because of it's higher tar content. – Owen C. Jones Feb 19 '14 at 10:12
  • But strictly speaking, isn't one drag of a cigarette more harmful than a drag of a marijuana joint in terms of tar content? – ssb Feb 21 '14 at 00:52
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    Well, realistically 'harmful' is too subjective a term. Very possibly, yes, cigarettes contain all sorts of introduced ingredients that cannabis doesn't. Too many variables I'd say. – Owen C. Jones Feb 21 '14 at 10:40
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    Surprised that no one has mentioned the role of filters in cigarettes, which are rarely (if ever) found in rolled joints. – Jiminy Cricket. Feb 26 '14 at 00:11
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    @Duckisaduckisaduck The Lung.org site [http://www.lung.org/associations/states/colorado/tobacco/marijuana.html] states "This is because marijuana joints are un-filtered and often more deeply inhaled than cigarettes." Which following the citations I found the likely source in http://oehha.ca.gov/prop65/hazard_ident/pdf_zip/FinalMJsmokeHID.pdf. Page 77, last paragraph is where that's likely sourced from. I ran out of comment space trying to include both comments. – QuinnG Mar 10 '15 at 18:13
  • It's also worth noting that there are many ways to smoke cannabis besides a joint. Filters actually aren't that rare, especially where cannibis is legal. Some "pre-rolled" joints come with filters and there are rolling papers that include filters. People can also smoke through a water pipe or a vaporizer, etc. Any of these have the potential to reduce the inhalation of tar. – sfmiller940 Oct 24 '19 at 22:01
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It appears marijuana leaves about 3x the tar as cigarettes.

As compared with smoking tobacco, smoking marijuana was associated with .. an approximately threefold increase in the amount of tar inhaled, and retention in the respiratory tract of one third more inhaled tar

What about the difference in smoking styles?

Significant differences were also noted in the dynamics of smoking marijuana and tobacco, among them an approximately two-thirds larger puff volume, a one-third greater depth of inhalation, and a fourfold longer breath-holding time with marijuana than with tobacco

This summary article talks about the cancer rates too.

For me, it raises the obvious question: what about vaporizers? One study I found is imperfect (no randomization, recruiting issues) but helpful for a baseline:

vaporizer users were less likely to report respiratory problems than patients who did not vaporize.. vaporizer users are only 40% as likely to report respiratory symptoms

tedder42
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According to the American Lung Association:

when equal amounts of marijuana and tobacco are smoked, marijuana deposits four times as much tar into the lungs. This is because marijuana joints are un-filtered and often more deeply inhaled than cigarettes.

Oddthinking
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Christina Moerschell
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    Welcome to Skeptics! While one might expect the American Lung Association to have expertise, this particular page provides no references to support the claim, so we have no way of knowing how they know this, or checking the original sources. – Oddthinking Jul 31 '14 at 03:14