How much do we know about cannabis and cancer?

Marijuana’s medicinal use dates back to ancient times, but its role in cancer care remains unclear today.

The legalization of medical marijuana in two dozen states has raised many questions among cancer patients. Could products made from a plant formally known as cannabis help ease cancer-related pain or nausea? Could it help patients gain weight or get a good night’s sleep? Many Internet sites suggest that cannabis products may actually shrink tumors. Is that true? Does marijuana have cancer-fighting properties?

So many unknowns

Doctors have many of the same questions, says Dr. Shauna Birdsall, Naturopathic Physician at our Phoenix hospital. That’s because the body of evidence is inconclusive. Marijuana’s medicinal use dates back to ancient times, but its role in cancer care remains unclear today. “Unfortunately, it isn’t a prescription medication where we understand the dose, indications and the potential side effects,” says Dr. Birdsall, who also serves as Medical Director of Naturopathic Medicine and Integrative Oncology at our Arizona hospital.  

The amount of active ingredients found in medical marijuana is also vastly inconsistent and unpredictable. More high-quality studies are needed, she says, especially since until recently, federal research restrictions have made it difficult for scientists to research marijuana’s health effects. Large studies tend to uncover new side effects, drug interactions and other complications. For example, Dr. Birdsall says, “a lot of natural products—green tea, curcumin, resveratrol—have really interesting anti-cancer effects, but we’re learning you need huge amounts to have an effect.”

In a recent paper published in the journal Current Oncology Reports, Dr. Birdsall and her colleagues outline what the scientific community knows and doesn’t know about medical marijuana’s potential in treating cancer and its side effects. After analyzing the data from more than 40 published reports, she and co-authors Dr. Lucas Tims and Dr. Timothy Birdsall say that time and further research may show that medical marijuana helps some cancer patients. But because the U.S. Drug Enforcement Administration continues to list marijuana as a Schedule I controlled substance, the federal government considers it illegal to prescribe, posing a significant barrier for doctors and patients alike.

Our brains, spinal cord and nerves are studded with tiny receptors that respond to so-called cannabinoids, the active chemicals found in marijuana. The receptors affect mood, memory, appetite and pain. Some studies have suggested cannabinoids may affect how cancer cells behave, causing them to live longer, invade other tissues, establish a blood supply and move throughout the body.  

What's the impact on pain?

In exploring whether marijuana may help ease the side effects of cancer and its treatment, Dr. Birdsall’s paper points out that a systematic review of 79 clinical trials on marijuana and its chemical ingredients concluded that cannabis had only a moderate impact on chronic pain and spasticity. The review also found little evidence that specific cannabinoids helped alleviate chemotherapy-related nausea and vomiting or improved weight gain and sleep disorders. As for short-term adverse effects, the review suggested that marijuana use may lead to a higher risk of dry mouth, anxiety, euphoria and psychosis , depending on the amount used and the patient’s reactions to it. “My preference would be for my patients to try approved medications, supplements that have shown benefits and other evidence-based supportive therapies,” Dr. Birdsall says. “We encourage patients to inform us if they are using medical marijuana, so we can include it in their chart and be aware in case they develop certain symptoms and side effects.”   

Because marijuana remains a controlled substance on the federal level, even though many states have legalized its medical use, doctors at Cancer Treatment Centers of America® (CTCA) do not prescribe it, Dr. Birdsall notes. Still, she’s aware that many patients have used medical marijuana to manage some of their cancer symptoms. “Overall, medical marijuana may have use in cancer care, but more research is needed to better inform physicians and patients,” Dr. Birdsall and her colleagues conclude in their paper.