Study: Smoking Marijuana Not Linked with Lung Damage

Marijuana smokers performed better on tests of lung function compared to nonsmokers and cigarette smokers

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Marijuana does not impair lung function—at least not in the doses inhaled by the majority of users, according to the largest and longest study ever to consider the issue, which was published today in the Journal of the American Medical Association.

Researchers working on a long-term study of risk factors for cardiovascular disease (the Coronary Artery Risk Development in Young Adults or CARDIA study) tested the lung function of 5115 young adults over the course of 20 years, starting in 1985 when they were aged 18 to 30.

They found that marijuana use was almost as common as cigarette smoking in the sample, which was designed to reflect the U.S. population.  Among participants, the average marijuana user toked 2-3 times a month, while the average tobacco user smoked eight cigarettes a day. Those who smoked both tended to do so slightly more frequently than those who smoked only cigarettes or only marijuana.

The study was “well conducted” and is “essentially confirmatory of the findings from several previous studies that have examined the association between marijuana smoking and lung function,” says Dr. Donald Tashkin, professor of medicine at UCLA and a leading scientist in the area. He was not associated with the new research.

“The major strengths of this study are that it included a far larger number of subjects followed for longer than any of these previous studies,” he adds.

MORE: Teen Drug Use: Marijuana Up, Cigarettes and Alcohol Down

While tobacco smokers showed the expected drop in lung function over time, the new research found that marijuana smoke had unexpected and apparently positive effects.  Low to moderate users actually showed increased lung capacity compared to nonsmokers on two tests, known as FEV1 and FVC. FEV1 is the amount of air someone breathes out in the first second after taking the deepest possible breath; FVC is the total volume of air exhaled after the deepest inhalation.

“FEV1 and FVC both actually increased with moderate and occasional use of marijuana,” says Dr. Mark Pletcher, associate professor of epidemiology and biostatistics at the University of California, San Francisco and the lead author of the study.

That was a bit of a surprise, says Pletcher, since “There are clearly adverse effects from tobacco use and marijuana smoke has a lot of the same constituents as tobacco smoke does so we thought it might have some of the same harmful effects. It’s a weird effect to see and we couldn’t make it go away,” he adds, explaining that the researchers used statistical models to look for errors or other factors that could explain the apparent benefit and did not find them.

MORE: Marijuana Slims? Why Pot Smokers Are Less Obese

The improvement wasn’t seen in the heaviest users, however. At high levels of marijuana use—for example, in those who smoked more than 20 times a month—FEV1 slipped back to levels seen in nonusers and a reduction was seen in, um, the most chronic smokers.  But FVC remained high in even the longest term, heaviest users.

So why might marijuana users have greater lung capacity than nonsmokers?  Consider Bill Clinton’s famous non-denial denial of his marijuana use, “I didn’t inhale” and Barack Obama’s retort that he “inhaled frequently; that was the point.”  Unlike cigarette smokers, cannabis users usually draw deeply on the joint or pipe— and hold each puff in, typically for as long as physically possible.

“In some ways, marijuana smoking is really a lot like doing a pulmonary function test,” Pletcher says. This “practice” or “exercise” might expand lung capacity and account for the unusual results.

He cautions, however, that long term exposure to marijuana smoke at the most extreme doses probably does damage the lungs, although he concedes that the evidence from the study on this point is “weak.”

The authors conclude:

Marijuana may have beneficial effects on pain control, appetite, mood, and management of other chronic symptoms. Our findings suggest that occasional use of marijuana for these or other purposes may not be associated with adverse consequences on pulmonary function. It is more difficult to estimate the potential effects of regular heavy use, because this pattern of use is relatively rare in our study sample; however, our findings do suggest an accelerated decline in pulmonary function with heavy use and a resulting need for caution and moderation when marijuana use is considered.

Since the study focused on cardiovascular disease and even the oldest participants had not yet reached the highest risk ages for lung cancer, it does not provide new information on cancer risk, but it does confirm the link between cigarette smoking and long-term lung function declines.

Tashkin, however, has studied this issue extensively. He says,  “The largest epidemiologic (case-control) study of the association between marijuana use and lung cancer failed to demonstrate that marijuana increases the risk of developing lung (or, for that matter, upper airway) cancer.”

He notes that a much smaller, recent study from New Zealand did claim to find a link, but only in very heavy users.  He says, “The authors’ interpretation of their data can be faulted because of the small numbers of their subjects exhibiting such heavy use, which rendered their estimates of risk imprecise.”

Why smoking marijuana and smoking tobacco should have such different effects on the lungs is still a matter of dispute.  Many researchers believe that it’s simply a matter of dose:  most marijuana users smoke a few times a month, while most cigarette smokers light up multiple times a day.

But Tashkin argues that specific properties of marijuana also matter.  He says that THC has anti-inflammatory and immune suppressing properties, which may prevent lung irritation from developing into chronic obstructive pulmonary disease (COPD), a devastating lung disorder frequently caused by tobacco smoking.

As for cancer, he says, “the THC in marijuana has well-defined anti-tumoral effects that have been shown to inhibit the growth of a variety of cancers in animal models and tissue culture systems, thus counteracting the potentially tumorigenic effects of the procarcinogens in marijuana smoke.”

Whatever the cause, it seems that those who argue that marijuana is harmful because of its smoke are going to have to find a different line of attack.

MORE: U.S. Rules That Marijuana Has No Medical Use. What Does Science Say?

Maia Szalavitz is a health writer at Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland’s Facebook page and on Twitter at @TIMEHealthland.


The substances in cannabis smoke

Cannabis smoke contains many of the same cancer causing substances (carcinogens) as tobacco - at least 50 of them. In addition, cannabis is often mixed with tobacco when smoked.

One of these carcinogens is benzyprene. Benzyprene is in the tar of both tobacco and cannabis cigarettes. We know that benzyprene causes cancer. It alters a gene called p53, which is a tumour suppressor gene. We know that 3 out of 4 lung cancers (75%) occur in people who have faulty p53 genes. The p53 gene is also linked to many other cancers.


Oh and where are the bodies of all these people who have been harmed by the use of marijuana?????


It is as we have said all along, prohibition was a scam foisted on us from the beginning!  It has failed spectacularly and should go the way of the dinosaur!


Obama could do a lot of good by taking Marijuana off the Drug Schedule.  Marijuana has been ILLEGAL for 70+ years! And what are the results?…

*Today marijuana is America's #1 cash crop. 

*Marijuana is stronger and easier to get than ever before, albeit much more expensive than it should be.  To smoke casually from the “black market”, it will run you $100/month.  This is much more expensive than it needs to be.  More expensive than my cell phone ($20/month from Tmobile), car insurance ($25/month from InsurancePanda), netflix ($10/month), and gym ($15/month from Planet fitness) COMBINED!!! Would you rather put money into the hands of violent gangs and drug dealers… or into taxes for schools, hospitals, public infrastructure, etc.???

*Today American kids can buy marijuana easier than they can buy a beer. 

*There are over half a million Americans in jail right now for non-violent drug crimes.

*Today marijuana is the #1 source of income for violent drug gangs and drug cartels who are richer and more dangerous than ever before. 

*Guns are illegal in Mexico yet Mexican drug cartels are buying machine guns, rocket launchers, grenades, airplanes, armored vehicles, anti-aircraft guns, and even submarines.

*The DEA has been having sex parties funded by drug cartels.

*The ATF/DOJ has given thousands of guns to drug cartels. 

I have this stupid thing I do called THINKING, and clearly I can see that marijuana prohibition can never work! America should have learned this simple lesson from alcohol prohibition!


Right...if you want believe that is a thorough and unbiased study I have a bridge in San Francisco I'd like to sell you.

-How many of them maintained smoking for the full 20 years? 

-How many were involved in physical exercise or sports? 

-How many had a high impact job (such as construction etc),

-How many were employed as people that sit around answering phones/non physical work?

-How many were employed at all? 

-When they arrived at this 'average", was it an even number across all people? Or were there a large group of people who -were heavy smokers and a couple who only smoked once or twice a year? 

-Were they pinners? Blunts? A pipe? Did they inhale? How much weed was actually consumed per sitting?

So many questions with no answers from this "study"...You cant do a half assed study, then publish it as an attempt to persuade people to legalize pot (which I think it should be btw) and expect people with more then 2 braincells to notice your study is a waste of time and money (and probably funded by democrats =p )


@AlexRompen You need to look more carefully at this study.  This study used an advanced experimental design that controlled for many of the factors that you mention.  Donald P. Tashkin is an American pulmonologistand a writer of many peer reviewed articles.  He is currently with the Division of Pulmonary and Critical Care Medicine, David Geffen School of Medicine, University of California at Los Angeles.Throughout 30 years of studying various medical cannabis he came up with a conclusion that it had a reduced risk to human health unlike tobacco that has a great impact on health, and can lead to many chronic illnesses and cancer. In 2006, he was in charge of the biggest case-control study which took in total of 2,200 subjects.  

While smoked marijuana does contain some of the same toxins as cigarettes or any other kind of smoke, smoking marijuana does NOT cause cancer. For a couple of reasons. Marijuana consumers inhale a tiny fraction of the smoke that cigarette smokers do. People standing on a busy street corner inhale more toxic smoke than the two or three puffs of marijuana. Also, marijuana has anti-cancer properties. The preeminent researcher of marijuana and lung disease, UCLA's Dr. Donald Tashkin, conducted investigations over 30 years, initially believing there must be a causal relationship. But he finally concluded that smoking marijuana does NOT cause cancer or ANY other serious disease. Tashkin explained, "We hypothesized that there would be a positive association between marijuana use and lung cancer, and that the association would be more positive with heavier use. What we found instead was no association at all, and even some suggestion of a protective effect."


Willie Nelson,Jimmy Page, John Paul Jones, Robert Plant, Snoop Dogg, the list goes on...and on...and on. And aren't all studies biased in one way or another? #urwelcome


Willie Nelson, Jimmy Page, Robert Plant, John Paul Jones, Snoop Dogg, the list goes on...and on...and on. And aren't all studies biased in one way or another? #urwelcome


*facepalm* the effectiveness is NOT because of the perceived pulmonary function test being applied at each turn; it's the synergism of the cannabinoids and terpenes acting as bronchodilators (which is barely a suggestion at the end of your article). That's why some cannabis makes us cough more than others, even in very high potencies. If they need a chronic user, I volunteer ;)

Real tokers know that it's small, short tokes that give us the most bang for our buck, as holding it in doesn't actually increase the absorption of THC. (do you get more O2 when you hold your breath, or do you just get dizzy?)  Spreading these kinds of misconceptions is dangerous. Isn't this TIME? Don't you guys research? Also, there are other ways to medicate through the pulmonary system, like vaporizing, which reduces the organic material significantly, practically eliminating the introduction of carcinogenic material to your lungs.


Great scoob though! Keep up with the good work. I am Paulite libertarian not liberal hippie. Heres..the deal.

Human brain morphology begins once alcohol & nicotine hit his bloodstream even if he lives happy for 200 years ever after. Junkscientists daren’t to say it because booze & tobacco revenues are essential to stop anarchy on Planet Earth. Booze & Tobacco revenue lands in the BIG-BROTHER pocket alas ‘The Establishment’[also known as the drug cartel in Latin America]. Unlike Marijuana. Its revenue lands in little pockets that the BIG-BROTHER loathes. Marijuana is one of 365,000 dangerous narcotics that generate $17T per year and lands tax-free in little pockets. It’s painful [four billion Dollars above the total US Economy/GDP]. Allow me to offer Holland metaphor. Marijuana sold in the Netherlands as Booze & Tobacco simply because Holland economy ain’t survive selling flowers. They need cash crop that can grow banknotes even if it kills babies in wombs. Health can wait. The Big Bang question is: who’re you dancing for? Junkscience! ‘The Establishment’ or the little pockets.


I believe the method of smoking marijuana   that we choose plays a big factor. I also think that smoke that is filtered well is the key. I found a great way of smoking marijuana that I truly believe is healthier. I definitely don't cough as I do with other methods.