What Cancer.gov Forgot to Say About Cannabis


The internet is abuzz with the word that the prestigious National Cancer Institute (NCI) has announced, through its website at cancer.gov, that the active ingredients in cannabis resin may be effective in killing cancer cells. The site’s FAQ page now includes a sampling of preclinical data listing some of the evidence for the ability of cannabinoids to inhibit or even kill tumors, including:

  • “Studies in mice and rats have shown that cannabinoids may inhibit tumor growth by causing cell death, blocking cell growth, and blocking the development of blood vessels needed by tumors to grow. Laboratory and animal studies have shown that cannabinoids may be able to kill cancer cells while protecting normal cells.”
  • “A study in mice showed that cannabinoids may protect against inflammation of the colon and may have potential in reducing the risk of colon cancer, and possibly in its treatment.”
  • “A laboratory study of delta-9-THC in hepatocellular carcinoma (liver cancer) cells showed that it damaged or killed the cancer cells. The same study of delta-9-THC in mouse models of liver cancer showed that it had antitumor effects. Delta-9-THC has been shown to cause these effects by acting on molecules that may also be found in non-small cell lung cancer cells and breast cancer cells.”
  • “A laboratory study of cannabidiol (CBD) in estrogen receptor positive and estrogen receptor negative breast cancer cells showed that it caused cancer cell death while having little effect on normal breast cells. Studies in mouse models of metastatic breast cancer showed that cannabinoids may lessen the growth, number, and spread of tumors.”
  • “A laboratory study of cannabidiol (CBD) in human glioma cells showed that when given along with chemotherapy, CBD may make chemotherapy more effective and increase cancer cell death without harming normal cells. Studies in mouse models of cancer showed that CBD together with delta-9-THC may make chemotherapy such as temozolomide more effective.”

Tantalizing stuff. Yet despite all of this data, the site still disclaims that “[a]t this time, there is not enough evidence to recommend that patients inhale or ingest Cannabis as a treatment for cancer-related symptoms or side effects of cancer therapy.” By way of explanation, the site maintains that “[n]o clinical trials of Cannabis as a treatment for cancer in humans have been found in the CAM on PubMed database maintained by the National Institutes of Health.”

This statement is technically true, but rather misleading. To test its veracity, I conducted my own search on the CAM on PubMed database for studies containing the keywords “cannabinoids” and “cancer.” The results came back with dozens of studies supporting the idea that cannabis and/or individual cannabinoids had some kind of antitumor, antiproliferative or improved quality of life effects for cancer patients, though admittedly the vast majority of them had methodologies similar to the studies cited by NCI: studies on mice, cancer cell lines in vitro, population-level data and so on.

Yet the search results were not devoid of human clinical trials: among others, they included this study from a 2011 issue of the Annals of Oncology which tested THC on adult cancer patients using a randomized, double-blind, placebo-controlled methodology (often called the “gold standard” in medical research) and which reported an increased quality of life for cancer patients given THC over those given placebo by improving appetite, sleep and the ability to relax. Anyone adept at splitting hairs could point out that this study didn’t actually study the use of cannabinoids to treat cancer — merely some of the symptoms of cancer and treatments like chemotherapy. But the studied cancer patients undeniably got better.

I also found this study from a 2006 issue of the British Journal of Cancer which tested the application of THC in humans who suffered from advanced glioblastoma multiforme, an extremely aggressive and deadly form of brain cancer. The study found that injection of THC into the tumors had the effect of triggering apoptosis (AKA “programmed cell death”) in the cancerous cells without damaging any healthy brain cells — a finding sure to have caused Ronald Reagan to turn over in his grave. The treatment also extended the lives of some, though not all, of the study participants. This is very promising research, although — once again, splitting fine hairs — technically the study was designed to study whether cannabinoids could be safely administered to cancer patients under a doctor’s supervision (spoiler alert: they can); the findings of the study related to actually treating cancer were just icing on the cake.

So is it actually too early to tell whether cannabis is an effective treatment for cancer, despite the reams of anecdotal reports of seemingly miraculous recoveries? More research is obviously needed, but given the clear and mounting evidence of the plant’s safety, it’s getting more and more difficult to maintain that cancer patients have anything to lose — unless, of course, their medical marijuana is contaminated.


Since graduating from Harvard Law School in 2008, Jeremy has devoted his career to educating voters and lawmakers on the consequences of cannabis prohibition and the available alternatives. He is the editor of TheLeafOnline.com, the digital reboot of the West Coast Leaf newspaper, and formerly worked as the Editor-in-Chief of Cannabis Now Magazine. Besides his work on MarijuanaPolitics.com, he also guest blogs for AlterNet Drugs, About.com, Salon.com and others.