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Cannabis & Cancer: What Do We Really Know?

Columnist: Peter Brett, M.D.
August, 2017 Issue

Peter Brett, M.D.
All articles by columnist

As an oncologist in Sonoma County for more than a quarter century, I see nearly 100 patients with cancer every week. As their doctor, care involves treating, counseling, supporting and listening to them. More than a third of those diagnosed with cancer will die from it, and no one escapes its effects on health. 

Many of my patients and their family members also want to know whether cannabis can help or hurt and how it’s used medicinally.

Parts of the cannabis sativa plant can be turned into many products these days, and you can get them into your body in a variety of ways. Cannabis can be smoked, vaped, eaten, and “dabbed” (which involves the flash vaporization of cannabis concentrates once applied to a hot surface and inhaled). The plant has more than 100 “cannabinoids,” related compounds that bind to cannabinoid receptors in the nervous system. The main two—tetrahydrocannabinol (THC) and cannabidiol (CBD)— are often put into cannabis products in different ratios. THC is the only cannabinoid that’s “psychoactive,” causing the euphoria of a marijuana high. THC is also formulated as dronabinol, a drug approved by the Food and Drug Administration (FDA), which has been around for 30 years.

Is cannabis an effective treatment? After a massive review of the current scientific literature published a few months ago by the National Academies of Sciences, Engineering, and Medicine, here’s how I respond to my patients’ questions.

1. Do cannabis products make a cancer go away and stay away? Though there are anecdotal cases of cancers receding with cannabis, there are no major, well-done studies in people that show a general benefit. Maybe some day there will be studies, but in the meantime, we have many proven and effective treatments for cancer that should be considered first. Nevertheless, at some point in their treatment, some patients opt to try cannabis products with different ratios of TCH and CBD. I believe that’s okay; there’s little harm in trying.

2. Are cannabis products effective in minimizing cancer symptoms such as nausea, pain, and poor appetite? Absolutely, however, the effect is only mild to moderate. For severe nausea or pain, we have better treatments, but cannabis products often have few side effects, which can be an advantage. It’s likely that THC helps best with nausea, but both THC and CBD may help relieve pain and improve appetite.

3. Do cannabis products help improve a sense of well-being? Studies show that patients with advanced cancer can have an improved sense of well being if they use cannabis that contains THC. However, some people don’t like the “high” feeling that THC causes.

Two case studies

Here are two examples, of patients who used cannabis as a medical treatment, which resulted in different outcomes. (Their social and clinical histories have been changed to maintain confidentiality.)

Case One: Patient LS is a 50-year-old woman, a tennis player, with prior sun exposure. She developed a serious skin cancer called melanoma, in the skin of her left arm, three years ago. This was surgically removed, but unfortunately the cancer spread extensively to her lungs a year later. We recommended treatment with immunotherapy, which has been approved by the FDA, but the patient opted to try cannabis oil that contained both THC and CBD. Though LS felt a little “spacey” and “forgetful” from the oil, remarkably, the melanoma in her lungs has gradually gone away. Now two years later, CAT scans show no sign of melanoma, and she’s probably cured. It’s possible the cancer might have spontaneously improved on its own, but cannabis certainly could’ve played a role.

Case Two: Patient RL is a 60-year-old man, a retired business executive, always in good health. A year ago he was losing weight and experiencing pain. An exam, blood tests and scans showed prostrate cancer, and it had spread to nearly all his bones. Chemotherapy and hormonal treatments helped for a time, but the cancer then quickly worsened. RL didn’t try another type of chemotherapy that we recommended, and instead took only cannabis oil with THC and CBD. Although he felt a little better for a few weeks, the cancer continued to grow rapidly, and he recently died.

It’s been more than 20 years since California legalized the medical use of cannabis, and this past November, the state voted to legalize nonmedical use of marijuana for those age 21 and older. One day, cannabis use may become as common as drinking wine in California. In the meantime, as its popularity grows, there’s still much to learn about cannabis as a treatment for cancer.

Peter Brett, M.D.
, is a board-certified medical oncologist at Sutter Medical Group of the Redwoods in Santa Rosa, and affiliated with the Sutter Santa Rosa Regional Hospital. He’s been practicing oncology for more than 25 years. For more information, go to, or call (707) 521-7750.


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