Medical marijuana may have a potential role in oncology for treating anticipatory and refractory chemotherapy-induced nausea and vomiting, for treating refractory cancer pain, and as an antitumor agent, a new review concludes. However, most of the evidence comes from small clinical trials and animal studies, many of which are outdated.

As a result, the authors call for more research and hesitate to recommend smoked marijuana as a first-line antiemetic. Neither would they recommend it as a first-line analgesic for cancer pain or as an antitumor agent.

The review of medical marijuana in oncology was published in JAMA Oncology. The senior author is Tina Rizack, MD, MPH, from the Alpert Medical School of Brown University, Providence, Rhode Island.

Patients May Ask

Twenty-three states and the District of Columbia have already legalized medical marijuana. While federal regulations still classify marijuana as an illegal substance, recent years have witnessed a trend by states to legalize it for medical and/or recreational use. Increasingly, patients may ask their doctors about the risks and benefits of marijuana use, the review authors write.

The antiemetic properties of cannabis are well known, they comment.

A previous review (BMJ. 2001;323:16-21) found that first-line use of cannabinoid derivatives may be more effective than various antiemetic drugs (prochlorperazine, metoclopramide hydrochloride, chlorpromazine, haloperidol, domperidone, or alizapride) in patients receiving medium emetogenic regimens (consisting of cyclophosphamide, methotrexate, or fluorouracil) but not highly emetogenic regimens (consisting of high-dose methotrexate, cisplatin, or doxorubicin and cyclophosphamide).

In addition, studies comparing derivatives of 9-tetrahydrocannabinol (THC, the most bioactive compound in marijuana) with other antiemetics have suggested that combined therapy may work best for nausea, though research is inconsistent.

Because of lack of evidence, the National Comprehensive Cancer Network Clinical Practice Guidelines in Oncology currently do not recommend marijuana for the treatment of chemotherapy-induced nausea and vomiting.

"Given the lack of data with regard to smoked cannabis as a form of treatment, it is not recommended as a first-line antiemetic," the review authors comment.

Clinical trials evaluating the analgesic properties of cannabinoids in cancer have been limited by small sample sizes, but they support the analgesic effects of THC and cannabinoid, even in opioid-refractory pain. However, sedation at high doses may limit its use.

"Because each study used different preparations of cannabis or THC, there is insufficient evidence to recommend cannabis or THC for the first-line management of cancer-associated pain, but the results suggest a benefit as an add-on medication," the authors write.

Compared with other analgesics, the safety profile of cannabinoids is favorable, they add. While studies have suggested that THC may be more sedating than codeine, THC is not associated with respiratory depression.

Some data suggest that THC may play an antitumor role and prevent metastasis, but most of the studies have been done in animals. Two clinical trials are evaluating the antitumor activity of cannabis in humans: a safety study comparing nabiximols to placebo in recurrent glioblastoma (NCT01812616) and a study of pure cannabidiol as a single-agent therapy for solid tumors (NCT02255292).

"Currently, there is insufficient evidence that cannabis or THC should be used for its antitumor properties outside of a clinical trial," the authors write.

Currently, cannabis is not a primary means of treatment for any cancer or treatment-related adverse effect. Rizack et al. Currently, cannabis is not a primary means of treatment for any cancer or treatment-related adverse effect.

Marijuana carries a low risk for overdose, with animal studies suggesting the lethal dose of cannabinoids is about 680 kg smoked in 15 minutes. Cannabinoid dependence is reported at 9% in long-term users, much less than addiction to heroin, cocaine, alcohol, and prescribed anxiolytics, they continue.

"Currently, cannabis is not a primary means of treatment for any cancer or treatment-related adverse effect. However, as marijuana legalization, access, and research increases, this may change," the authors conclude.

They also call for more research in all areas related to medical marijuana use.

The authors have disclosed no relevant financial relationships.

JAMA Oncol. 2016;2:670-675. Abstract

Follow Medscape Oncology on Twitter: @MedscapeOnc