[Dear readers, This post is by my brother, Ed Gogek, MD, an Arizona physician who was very active in opposing Arizona’s new medical marijuana law. The following excerpt was written as comment on new regulations for the AZ law. His position is that regs should ban medical marijuana in the smokeable form. Here’s a link to his blog, where the entirety of the post can be found. jg]
As a doctor, I oppose dispensing medical marijuana in a form that can be smoked. The medical profession and others in public health have made a huge effort for several decades to eliminate the smoking of tobacco because it’s such a serious health hazard, and doctors should not recommend any substance to be smoked.
Research evidence shows that smoking marijuana probably causes respiratory problems and several types of cancer, including lung cancer. The evidence is not overwhelming, mostly because there have not been enough good studies, but it’s significant.
On several pro-marijuana websites I found the claim that “there is no direct evidence linking marijuana smoking to lung cancer in humans.” That is exactly what the tobacco industry said for decades after the first studies came out linking cigarette smoking with lung cancer. What they said was technically true; until recently we did not know for certain the exact mechanism by which smoking caused cancer. However, the statistical evidence was overwhelming, so the tobacco industry was being completely disingenuous and so are the pro-marijuana groups who say marijuana doesn’t cause cancer. Anyone who claims that marijuana does not cause cancer is ignoring the research.
Two studies showed no increase in cancer in marijuana users, but negative studies are not proof unless it happens repeatedly. Also, both studies have been criticized for bias, and I believe these criticisms are accurate. One large study (Tashkin 2006) of 1200 people with head, neck and lung cancer showed no increase in cancer in marijuana smokers. Tashkin was the same researcher who had previously found that marijuana caused pre-cancerous changes in the respiratory tract, so he was surprised to find no increased cancer risk. That large study has been criticized for selection bias—marijuana users in the control group were more likely to also smoke cigarette than the marijuana users in the group with cancer, so they did not do a good job of controlling for cigarette smoking. This really throws doubt on the results.
One other study published in the American Journal of Public Health in 1997 (Sidney et al) that found marijuana smokers had no increase in cancer has been criticized for using subjects who were too young, so cancers would not have had time to develop.
There is also research showing increased cancer rates in marijuana smokers.
A New Zealand study published in the European Respiratory Journal in 2008 looked at 79 patients with lung cancer and found the risk of lung cancer increased by 8 percent for every joint-year (averaging one joint daily for one year) and 7 percent for every pack-year (averaging one pack of cigarettes daily for one year), leading them to conclude that smoking marijuana posed the same lung cancer risk as smoking cigarettes.
Three North African case studies showed a very strong link between marijuana smoking and lung cancer, but none of these studies controlled for tobacco use, so these results are questionable.
A 2009 study done at the Fred Hutchinson Cancer Research Center in Seattle and published in the journal Cancer found that men who smoked marijuana once a week had twice the risk of testicular cancer when compared to men who never used marijuana, and marijuana was most strongly linked to nonseminoma, the most aggressive form of testicular cancer.
Research published in the journal Urology in 2006 showed increased rates of bladder cancer in marijuana smokers. They also found that marijuana-smoking patients were younger at the time of diagnosis than most patients with bladder cancer. Cigarette smoking is a major risk factor for bladder cancer, but the researchers concluded that smoking marijuana may be as bad or worse than cigarette smoking as a risk factor for bladder cancer.
In 1999, a study published in the journal Cancer Epidemiology found that squamous cell carcinoma of the head and neck increased with marijuana use and there was a strong dose-response curve, the heavier marijuana users had higher rates of cancer. However, in 2004, a study published in Cancer Research found no association between marijuana user and squamous cell carcinoma.
This is not a complete list of studies, but there aren’t many. So it is not enough to draw definitive conclusions on marijuana and cancer. However, the evidence that marijuana smoking is linked to cancer is far more substantial than the research supporting marijuana as treatment for most of the disorders listed in Arizona’s new medical marijuana law. Also, remember, it took decades of heavy tobacco use by large swaths of the population before we had a definitive link between smoking and cancer.
Also, in November 2010 an article printed in the European Journal of Immunology described a possible mechanism by which smoking marijuana causes cancer and the research supporting this possible mechanism. If further studies support these findings, then we will have direct evidence linking marijuana smoking to cancer in humans.
Anyone who goes on the internet will find the pro-marijuana groups misrepresenting research. What they almost always do is take one study or one bit of information and run with it as if that were the whole story. That’s how Arizona ended up with a law that says marijuana is good for glaucoma even though the Glaucoma Foundation warns patients not to use marijuana because it could make their symptoms worse.
There are even pro-marijuana websites claiming that marijuana cures cancer. This comes from research showing that certain cannabinoids might have an anti-tumor effect, but the same research also showed that marijuana smoke contained many of the same carcinogens found in tobacco or that marijuana suppresses the immune system making cancer more likely, and the pro-marijuana groups never mention that.
The American Cancer Society points out on its website that it’s hard to study marijuana and cancer because so many marijuana users also smoke cigarettes and because it’s hard to study illegal drugs. British cancer researchers noticed the same problem. Both noted a weak link between marijuana and cancer based on very limited research. Not definitive, but not negligible.
One part of the research is very clear. We know for certain that marijuana smoke contains many of the same carcinogens as tobacco smoke, produces more tar than tobacco, and that the way people smoke marijuana (down to the roach, unfiltered, inhaling deeply, holding it in) delivers more tar to the lungs than the way people smoke tobacco.
Calfornia’s Office of Environmental Health Hazard Assessment ruled in 2009 that marijuana smoke is carcinogenic. They are not calling the marijuana plant a carcinogen, just the smoke. That seems right; the research shows a link between smoking marijuana and several types of cancer also commonly caused by smoking tobacco. There is no evidence that ingesting marijuana by other methods causes cancer.
Smoking marijuana is also linked to respiratory problems. Research shows that marijuana smokers have decreased respiratory function, increased airflow obstruction, and fewer of the anti-oxidants that protect against cancer and heart disease.
In summary, smoking marijuana has been implicated in several health problems including cancer. So no doctor should be recommending marijuana in a form that can be smoked. And states with medical marijuana laws, including Arizona, should not allow such a dangerous route of administration. Following the basic dictum, First, do no harm, doctors should always prescribe medications by the least harmful route of administration.
We always try to put medications in a form that can be taken orally. For people whose illness makes it hard to take a pill or to keep one down, we have skin patches and suppositories. The last resort is injecting medicine. But there is no precedent for a medication that is smoked, and for good reason. Smoking causes cancer and lung damage.