Dumb New Myths About Marijuana
A much-publicized new study is raising doubts about the harmful effects of pot. But it's dangerously hazy on the facts.
On Tuesday, major newspapers and pro-pot blogs alike published stories with the headline “Marijuana use does not harm the lungs.” They reported a surprising finding in a study of over 5,000 people, published in the Journal of the American Medical Association, that occasional marijuana use did not harm the lungs. Heavier use, such as very frequent use, as well as occasional tobacco use, however, did show a decline a lung function. Most surprisingly, the study’s authors speculate that the mild beneficial effects they found in occasional marijuana smokers could be due to enhanced lung capacity resulting from the heavy and extended inhalations entailed in marijuana smoking. On the flip side, since beneficial lung effects were only observed in occasional marijuana smokers, the authors speculate that exposure to potential toxins was insufficient to outweigh or undo the observed benefits they report.
It's an intriguing study. After it was published, some former Oxford colleagues and I looked at the researcher’s methods and study design. We didn’t find anything in the study design to question its methodology. Yes, it would have made sense to test the THC levels of marijuana in these smokers, who started using 20 years ago, when the THC and tar levels were much lower than they are today. But the researchers followed standard protocol, and there is no reason to believe they had a pre-set agenda. They were, by all news accounts, judicious and cautious about making grand claims about marijuana’s positive health effects.
In fact, the lead researcher admitted that “Marijuana is clearly an irritative smoke for the lungs,” citing coughing after taking a “hit” to illustrate his point.
This study looked at one single outcome—lung capacity. The truth is that marijuana is linked to all kinds of respiratory problems, and studies have consistently shown this, although they barely gain much attention—perhaps because people have come to expect such findings. Long-term studies from the USA and New Zealand have shown that regular cannabis smokers report more symptoms of chronic bronchitis than non-smokers. There is a four-fold greater quantity of cannabis smoke particles (tar) in the respiratory tract compared to the tar generated from the same amount of smoked tobacco. Again, the way marijuana is smoked may have something to do with this: marijuana smokers hold their breath significantly longer than tobacco smokers. Interestingly, this latest study shows that the heavy breathing in done by the occasional marijuana smokers may help them—but only in the short run, since more frequent use seems to wipe out any benefit. But marijuana smoke also includes an enzyme that converts some hydrocarbons into a cancer-causing form, potentially accelerating the changes that produce malignant cells. Animal lungs exposed to cannabis smoke developed abnormal cell growth and accelerated malignant transformation, to a greater extent than those exposed to tobacco. An interesting note is that researchers caution HIV positive individuals who smoke cannabis may be predisposed to pulmonary infections and pneumonia, a consequence that no doubt warrants further investigation.
Sadly, advocates caught up in their adulation of the JAMA finding neglected to mention any of these findings from the over four decades of research tying marijuana use to mucosal injury, inflammation, increased cough and phlegm production, and wheezing. They also left out marijuana’s link to increased bronchitis, worsening of asthma symptoms, and worsening of cystic fibrosis symptoms. (In case you’re wondering, the evidence linking marijuana and lung cancer are mixed, with a recent study stating that “cannabis smoking increases the risk of developing a lung cancer independently of an eventual associated tobacco exposure.” Other studies have failed to find such a link.)
I asked a few other experts for their take on the study. Mark Gold, perhaps the most distinguished professor in the country on drugs and the brain and body, told me, “It is possible, but not proven, that cannabis smoke may be less toxic than cigarette smoke, but it is not better than clean air. Clear, unbiased, and convincing evidence of safety and comparable efficacy are needed for therapeutic claims. It is smoke, after all.”
“Columbus brought Tobacco to the 'New World' and it took nearly 500 years for absolute proof of tobacco smoke dangerousness to be established,” Gold continued. “To this day, each year, over 400,000 United States deaths are due to tobacco smoke. We had occasional tobacco smokers in the 18th century and textbooks written describing the wonders and medicinal value of tobacco smoking. The occasional smoker increasingly becomes an anachronism with increased access augmented by social marketing, claims of therapeutic efficacy, reduced stigma and price.”
Bob DuPont, the man who introduced modern drug treatment to Washington D.C. and served three presidents as founding director of the National Institute on Drug Abuse, said, “Every user of alcohol or marijuana starts out intending to be a moderate, infrequent user and is quickly reassured that this goal is easily achieved. But it does not work out that way for a significant proportion of those initial users.”
Furthermore, he asks, “What other health-related advice is justified when a large minority of people who take that advice suffer terrible—often fatal—consequences?”
Indeed, one could imagine a study on speeding that would show the vast majority of people who speed do so safely and get to their destinations faster than those who obey speed limits. They are not arrested and have no accidents—in fact, for some reason researchers are still not sure about, they tend to have significantly less accidents than slower drivers. But that doesn’t mean we would suddenly approve of speeding and promote its activity.
We still have a long way to go to fully understand how, why, and if marijuana affects all different kinds of bodily functions, and certainly this new research should lead us to more serious study of marijuana’s effect on the lungs specifically. Any objective look at the existing science will show that marijuana causes decreased cognitive skills (including attention, motivation, memory and learning), as well as impaired driving, psychosis, or panic during intoxication, and addiction, which occurs in about one in every 10 users (a number similar to alcohol, and lower than cocaine, which addicts about one in six people who ever use it). There is no doubt that this finding on lung function and marijuana gives us much to mull over. For example, a longitudinal study is needed that looks at current trends of high dose marijuana and heavy users, especially those using frequently for “medical purposes.” But to say that marijuana smoke is now good for you, as some have suggested, is both disingenuous and dangerous.
Kevin A. Sabet, Ph.D., a newly appointed assistant professor at University of Florida's School of Medicine, is a regular columnist at The Fix and Huffington Post and a former Obama Drug Policy Adviser. He took a long, deep breath of Manhattan air before writing this article from his favorite coffeeshop in Greenwich Village. He is based in Cambridge, Massachusetts.