Study Finds No Cancer-Marijuana Connection

The largest study of its kind has unexpectedly concluded that smoking marijuana, even regularly and heavily, does not lead to lung cancer.

The new findings “were against our expectations,” said Donald Tashkin of the University of California at Los Angeles, a pulmonologist who has studied marijuana for 30 years.

“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,” he said. “What we found instead was no association at all, and even a suggestion of some protective effect.”

Federal health and drug enforcement officials have widely used Tashkin’s previous work on marijuana to make the case that the drug is dangerous. Tashkin said that while he still believes marijuana is potentially harmful, its cancer-causing effects appear to be of less concern than previously thought.

Earlier work established that marijuana does contain cancer-causing chemicals as potentially harmful as those in tobacco, he said. However, marijuana also contains the chemical THC, which he said may kill aging cells and keep them from becoming cancerous.

Tashkin’s study, funded by the National Institutes of Health’s National Institute on Drug Abuse, involved 1,200 people in Los Angeles who had lung, neck or head cancer and an additional 1,040 people without cancer matched by age, sex and neighborhood.

They were all asked about their lifetime use of marijuana, tobacco and alcohol. The heaviest marijuana smokers had lighted up more than 22,000 times, while moderately heavy usage was defined as smoking 11,000 to 22,000 marijuana cigarettes. Tashkin found that even the very heavy marijuana smokers showed no increased incidence of the three cancers studied.

“This is the largest case-control study ever done, and everyone had to fill out a very extensive questionnaire about marijuana use,” he said. “Bias can creep into any research, but we controlled for as many confounding factors as we could, and so I believe these results have real meaning.”

Tashkin’s group at the David Geffen School of Medicine at UCLA had hypothesized that marijuana would raise the risk of cancer on the basis of earlier small human studies, lab studies of animals, and the fact that marijuana users inhale more deeply and generally hold smoke in their lungs longer than tobacco smokers — exposing them to the dangerous chemicals for a longer time. In addition, Tashkin said, previous studies found that marijuana tar has 50 percent higher concentrations of chemicals linked to cancer than tobacco cigarette tar.

While no association between marijuana smoking and cancer was found, the study findings, presented to the American Thoracic Society International Conference this week, did find a 20-fold increase in lung cancer among people who smoked two or more packs of cigarettes a day.

The study was limited to people younger than 60 because those older than that were generally not exposed to marijuana in their youth, when it is most often tried. (source)



10 thoughts on “Study Finds No Cancer-Marijuana Connection

  1. I’d like to see a more recent study on that “marijuana has 50% more tar than cigarettes” study. I think it must be 30 years old, having used outdated, less accurate testing equipment, and subject to severe bias based on the uncontrolled lack of truth surrounding marijuana, which may have been fueled by the unbridled public fear of said medicinal plant.


  2. Tobacco is a tar based plant. Marijuana is an oil based plant. Tar based plant smoke lies dormant in the lungs eventually building up an unmoveable chunk of tar and causing emphysema and the need for oxygen tanks. Marijuana, especially if vaporized, actually loosens up any flem in the lungs allowing the patient to cough it up and expel it. I coughed up at least 1 cup of flem the first month of vaporizing rather than smoking. After every vaporization session my bronchial airways, as pointed out above, were clear and my breathing was actually made easier. Vaporizing marijuana removes all dangers from smoking by removing all the Tars and Carcenigens found in marijuana smoke. In addition vaporizing delivers all the Cannabinoids, and only the cannabinoids, if vaped at a temp below 392 degrees farebheit the temp at which marijuana will combust. I highly recommend you invest a minimum of $200 for the best and cheapest vaporizer made the V-Tower Vaporizer made by Arizer Co. in Canada. It comes with a life time gaurentee on the heating element. You will not be dissapointed.


  3. Pingback: Study Finds No Cancer-Marijuana Connection « Patients for Medical Marijuana |

  4. There is an opposite opinion of sorts from a study over in the U.K. I wonder if scientist know what the hell their doing at times. One says it is cancerous and the other it is not. Or, it maybe that someone can say that the marijuana damaged some cells so that could lead to cancer, thus Marijuana causes cancer. It makes one’s mind numb. For what it is worth I frankly don’t care! I think Marijuana should be legalized. Others of course disagree OK.


    • Brad,

      Thanks for this. It is pure propaganda. There still has been no link between cancer and smoking cannabis. This is a scare tactic so that cannabis is never re-legalized. There is an interesting correlation between the timing of recent triumphs on the legalization front and this news. It isn’t news.

      Finding someone who got cancer from smoking cannabis is news.

      Further, medical cannabis, if one is using high quality buds, requires as little as 4 puffs for an entire day. These studies are using entire joints (20 puffs or so) to come up with their numbers. They also fail to mention that many cannabis users prefer to eat, drink or vaporize their medicine, which 100% alleviates the risk.


      • The term “medical marijuana” is an oxymoron – there’s no such thing. Marijuana has no medical properties. Ask any honest doctor.


    • For every peer reviewed medical study on marijuana, there are 80 psuedo-science opinions by pro-marijuana advocates. The facts are out there, but the marijuana smoke is thick…


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