A brand-new study linking marijuana with increased lung capacity has the nation in a tizzy, talking about whether toking actually boosts our respiratory fitness. Few scientific subjects are as controversial and politically volatile as the health effects of cannabis. For every report linking pot with pain reduction, you’ll find three more linking it with schizophrenia, suicidal tendencies, and sinking sperm counts. Here’s a spate of studies showing that this conversation is anything but finished.
1. Otherwise healthy men who have smoked the equivalent of one joint daily for seven years have a lung capacity that is 1.6 percent higher than that of otherwise healthy non-marijuana-smoking men.
Based on 20 years of research involving 5,115 adults, the study that yielded this stat—affiliated with the University of California, San Francisco, the National Institute on Drug Abuse, and other agencies, and published in this month’s Journal of the American Medical Association—confirmed earlier studies linking cannabis and increased lung capacity. Sounds promising. “But the size of this increase is not very big, and it’s not necessarily a sign of actually improved lung health,” cautions University of Alabama School of Medicine Associate Professor Stefan Kertesz, the study’s lead author. “The net increase is only 50 milliliters. A soda can is 350 milliliters, so we’re talking about an amount that’s one-seventh the size of a soda can.” And with further marijuana use, lung capacity declines.
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Mark Pletcher, et al. “Association Between Marijuana Exposure and Pulmonary Function Over 20 Years.” Journal of the American Medical Association, 307 (2): 173–81.
2. If you smoke marijuana, you’re inhaling 20 times as much ammonia as you would inhale by smoking the same amount of tobacco.
According to the study that yielded this stat, “The confirmation of the presence, in both mainstream and sidestream”—that is, directly inhaled and secondhand—“smoke of marijuana cigarettes of known carcinogens and other chemicals implicated in respiratory diseases is important.” This Canadian government-affiliated study also found three times as much ammonia in secondhand marijuana smoke as in secondhand tobacco smoke.
David Moir, et al. “A Comparison of Mainstream and Sidestream Marijuana and Tobacco Cigarette Smoke Produced Under Two Machine Smoking Conditions.” Chemical Research in Toxicology, 21(2): 494–502.
3. People who smoke marijuana three times a week are about half as likely as non-marijuana smokers to be obese.
Are the munchies a myth? The authors of the 2011 French study that yielded this stat, published in the American Journal of Epidemiology, were inspired to do this research because while “the role of cannabis and endocannabinoids in appetite regulation has been extensively studied, the association of cannabis use with weight in the general population is not known.” After examining two previous epidemiological studies, the authors had to “conclude that the prevalence of obesity is lower in cannabis users than in nonusers.”
Yann Le Strat and Le Foll, Bernard. “Obesity and Cannabis Use: Results From Two Representative National Surveys.” American Journal of Epidemiology, Aug. 24, 2011.
4. People who start smoking marijuana in adolescence or young adulthood are nearly twice as likely as non-marijuana smokers to develop symptoms of psychosis.
Published in the British Medical Journal and affiliated with the Netherlands’ Maastricht University, the study that yielded this stat tracked 1,923 individuals who were ages 14 to 24 when the research began. “The use of cannabis is consistently associated with mental illness, in particular psychotic disorder,” its authors write. “It remains a matter of debate, however, whether the association between cannabis and psychosis is causal, or whether early psychotic experiences might in fact prompt cannabis use as a means of self-medication.” Which came first: the reefer or the madness?
Rebecca Kuepper, et al. “Continued Cannabis Use and Risk of Incidence and Persistence of Psychotic Symptoms: 10-Year Followup Cohort Study.” British Medical Journal, March 1, 2011.
5. A neurotransmission system in the brain that affects pleasure, memory, perception, and coordination is 20 percent less active in regular marijuana smokers than in non-marijuana smokers.
So that’s why you suck at Ping-Pong. The National Institute of Mental Health– and National Institute on Drug Abuse–affiliated researchers who conducted the study that yielded this stat used positron emission tomography to compare the brains of otherwise healthy daily marijuana smokers with the brains of otherwise healthy nonsmokers. They found that the cessation of marijuana use corrected the problem.
Jussi Hirvonen, et al. “Reversible and Regionally Selective Downregulation of Brain Cannabinoid CB1 Receptors in Chronic Daily Cannabis Smokers.” The Journal of Nuclear Medicine, 52 (Supplement 1):10.
6. One and a half times as many current marijuana smokers as nonsmokers have asthma.
At least this applies to participants in the Yale University–affiliated study that yielded this stat, which defines current marijuana users as those who have smoked marijuana at least 100 times throughout their lives and at least once in the last week. Among its participants, 5.8 percent of current marijuana smokers had asthma, compared with 6.5 percent of tobacco smokers and 3.8 percent of nonsmokers.
Brent Moore, et al. “Respiratory Effects of Marijuana and Tobacco Use in a U.S. Sample.” Journal of General Internal Medicine, 20 (1): 33–7.
7. Longtime marijuana smokers are only one third as likely to contract head-and-neck squamous-cell carcinoma as are non-marijuana smokers.
Pot-smoking sun-lovers will cherish the Brown University–affiliated study, published in Cancer Prevention Research, that yielded this stat. “Ten to 20 years of marijuana use was associated with a significantly reduced risk of HNSCC,” its authors write. “The magnitude of reduced risk was more pronounced for those who started use at an older age,” they add. Anyone got a light?
Caihua Liang, et al. “A Population-Based Case-Control Study of Marijuana Use and Head and Neck Squamous Cell Carcinoma.” Cancer Prevention Research, July 28, 2009.
8. People who have inhaled marijuana within the last hour are nearly five times more likely to have heart attacks as people who have not inhaled marijuana in the last hour.
The trouble with extreme stats such as this one, drawn from a Spanish study published in the British Medical Journal’s Journal of Neurology, Neurosurgery & Psychology, is that they tempt us to jump to conclusions—thanks, Kertesz says, to “the unsettled nature of our public discourse on marijuana. When there’s a single piece of information on a single organ system ... we’re drawn to it like moths to a flame, as if this one piece of information would clarify everything.”
I. Mateo, et al. “Recurrent Stroke Associated with Cannabis Use.” Journal of Neurology, Neurosurgery & Psychology, 76: 435–7.
9. Young adults who have smoked marijuana for more than six years are four times as likely as non-marijuana smokers to become delusional.
Affiliated with Australia’s University of Queensland, the study that yielded this stat used the Peters et al. Delusions Inventory, a standard psychological tool that asks users whether—among other things—they feel possessed, persecuted, victimized by conspiracies, controlled by electrical devices, cursed with rotting entrails, able to read minds, gifted with superhuman powers, destined for fame, and/or “especially close to God.” Its questions include: “Do you ever feel as if you are a robot or zombie without a will of your own?” and “Do you ever feel as if things in magazines or on TV were written especially for you?”
John McGrath, et al. “Association Between Cannabis Use and Psychosis-Related Outcomes Using Sibling Pair Analysis in a Cohort of Young Adults.” Archives of General Psychiatry, 67 (5): 440–7.
10. If you smoke marijuana, you’re inhaling three to five times as much hydrogen cyanide as you would inhale by smoking the same amount of tobacco.
The Canadian government–affiliated study that yielded this stat also found what its authors called “significantly higher” levels of mercury, cadmium, nickel, lead, and chromium in marijuana smoke than in tobacco smoke. Where did the researchers get their weed? “A standardized, quality-controlled, dried marijuana product, made of flowering heads only, reference H55- MS17/338-FH, was obtained from Prairie Plant Systems Inc. in Saskatoon.”
David Moir, et al. “A Comparison of Mainstream and Sidestream Marijuana and Tobacco Cigarette Smoke Produced Under Two Machine Smoking Conditions.” Chemical Research in Toxicology, 21(2):494–502.
11. People who smoke both tobacco and marijuana are three times more likely than nonsmokers to develop chronic obstructive pulmonary disease.
COPD—emphysema and chronic bronchitis rolled into one—severely inhibits airflow in the lungs and is the third leading cause of death in the U.S. Published in the Canadian Medical Association Journal, the study that yielded this stat also found that people who smoke both tobacco and marijuana are 2.5 times more likely than nonsmokers to have respiratory problems in general. “Smoking marijuana (at least in relatively low doses) may act as a primer, or sensitizer, in the airways to amplify the adverse effects of tobacco on respiratory health,” write its authors.
Wan Tan, et al. “Marijuana and Chronic Obstructive Lung Disease: A Population-Based Study.” Canadian Medical Association Journal, 180 (8): 814–20.
12. Drivers under the influence of marijuana are more than twice as likely as other drivers to be involved in motor-vehicle accidents.
The Columbia University–affiliated team who conducted the 2011 study that yielded this stat drew on nine epidemiological studies to find that drivers who have smoked marijuana in the last three hours or test positive for marijuana face double the car-crash risk of non-marijuana-smoking drivers. The study also found that the higher the marijuana concentrations in the urine, the higher the crash risk. Whatever marijuana does to the body and brain, it does not play well with cars.
Mu-Chen Li, et al. “Marijuana Use and Motor Vehicle Crashes.” Epidemiologic Reviews, Oct. 4, 2011.
13. The lungs of otherwise healthy men who have smoked the equivalent of one joint daily for seven years have 1.25 percent more efficient airflow than the lungs of otherwise healthy non-marijuana-smoking men.
The UCSF-affiliated pot-lung study that yielded this stat confirmed similar previous findings—“but that gain is very limited in size,” says Kertesz, its lead author. He raises the possibility that years of toking practice—sucking hard, holding the breath, exhaling slowly—might be the airflow-altering factor rather than cannabis itself: “Maybe there’s some training benefit in the sense that through the act of smoking marijuana, you’re familiar with the technique” by which airflow is measured, he says. Bummer, man: after seven “joint-years,” the airflow increase goes into reverse.
Mark Pletcher, et al. “Association Between Marijuana Exposure and Pulmonary Function Over 20 Years.” Journal of the American Medical Association, 307 (2): 173–81.
14. Multiple-sclerosis patients who smoke marijuana are twice as likely as non-marijuana-smoking M.S. patients to be cognitively impaired.
The 2011 University of Toronto-affiliated study that yielded this stat compared pot-smoking and non-pot-smoking MS patients. “Cannabis users performed significantly more poorly than nonusers on measures of information-processing speed, working memory, executive functions, and visuospatial perception,” its authors write. “On a sensitive test of information-processing speed, those using marijuana scored approximately one-third lower than non-users ... Whatever subjective benefits patients may derive from using street cannabis (e.g., pain and spasticity relief) should be weighed against the associated cognitive side effects.”
Kinia Honarmand, et al. “Effects of Cannabis on Cognitive Function in Patients with Multiple Sclerosis.” Neurology, 76 (13): 1153–60.
15. Nearly five times as many regular marijuana smokers as nonsmokers have chronic phlegm.
In the Yale University-affiliated study that yielded this stat, 14.6 percent of regular marijuana smokers had chronic phlegm, compared with only 3.5 percent of nonsmokers. But at 16.9 percent, tobacco smokers out-phelgmed them both. “Marijuana is an irritating substance,” Kertesz says. “Everyone knows that. If you’ve ever watched a Harold and Kumar movie, you know that when Kumar smokes marijuana, he starts hacking. The question is whether this irritating substance causes long-term harm.” And the scientific jury is still arguing about that.
Brent Moore, et al. “Respiratory Effects of Marijuana and Tobacco Use in a U.S. Sample.” Journal of General Internal Medicine, 20 (1): 33–7.
