Cancer patients often attest to the benefits of medical marijuana to help ease nausea and pain, but rock solid evidence of benefit does not exist, say the authors of a comprehensive review on the topic.
"Marijuana in oncology may have potential for use as an antiemetic, for refractory cancer pain, and as an antitumor agent, but more research is needed in all areas to clearly define benefit," Tina Rizack, MD, MPH, a medical oncologist at the Warren Alpert Medical School of Brown University, Providence, Rhode Island, told Medscape Medical News.
Medical marijuana is now legal in 23 states and the District of Columbia, and chances are good that a physician anywhere in the country will be asked about it at some point. "Many of our patients ask for medical marijuana licenses and inquire about the benefits of marijuana, [but] there were no reviews available in the literature to guide discussion," Dr Rizack said.
Dr Rizack's and colleagues' review, published online March 17 in JAMA Oncology, covers the history, adverse effects, and proposed mechanisms of action of marijuana and summarizes the current literature regarding symptom relief and therapeutic value in cancer patients.
Cannabis is known for its antiemetic properties, which makes it an appealing treatment for chemotherapy-induced nausea and vomiting, the authors note. It has "anecdotally" been effective in suppressing anticipatory nausea. Yet, the exact mechanism of action remains unclear, they point out.
"There are currently no clinical trials comparing smoked cannabis to current first-line antiemetic therapies.... [I]t is not recommended as a first-line antiemetic," Dr Rizack and colleagues write.
Cannabinoids have also been studied for their analgesic potential in cancer-associated pain, specifically, neuropathic pain.
But because each study used different preparations of cannabis or delta-9-tetrahydrocannabinol (THC), the active component, "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 observe.
More clinical trials examining the effects of smoked cannabis and its derivatives, such as THC, on pain are needed, they also say.
However, the authors of the new review may be outsiders on the subject, suggested an expert who was not involved with the article.
"This is a very thorough review, but I can suggest a caveat to consider," David Casarett, MD, told Medscape Medical News. "The authors provide recommendations about whether medical marijuana should be first-line treatment for these symptoms, but in my experience, that's not how it's used."
Dr Casarett is director of hospice and palliative care, Penn Medicine, is a professor of medicine at the University of Pennsylvania Perelman School of Medicine, in Philadelphia, and is the author of the book, Stoned: A Doctor's Case for Medical Marijuana (Penguin Random House).
"In researching Stoned, I spoke with dozens of patients, many of whom had cancer, and they all told me that they turned to medical marijuana after other treatments had failed. Sometimes those other treatments didn't work, or sometimes those other treatments had unacceptable (for them) side effects. But evaluating marijuana as a first-line treatment sets the bar much higher than most patients do," Dr Casarett said.
"I think it's plausible ― even likely ― that patients could get some benefit from medical marijuana for some symptoms, either in addition to first-line treatments or as second- or third-line options when more traditional treatments fail," he argued.
"Also, let's be honest, for some people, the euphoria of marijuana is part of the attraction. That's certainly not the only 'benefit' of marijuana for patients with cancer, and probably isn't the most important benefit for many patients. But it is for some," Dr Casarett pointed out.
"Don't Bet Your Life on It"
Dr Rizack and colleagues note in their review that there is some evidence to suggest that cannabis may be a potential chemotherapeutic agent, but that evidence is mostly based on animal models. "Currently, there is insufficient evidence that cannabis or THC should be used for its antitumor properties outside of a clinical trial," they conclude.
Dr Casarett agrees and has a sad supporting anecdote.
The authors are to be "commended for their warning that medical marijuana shouldn't be used for its antitumor effects," he commented "True, there is some intriguing science from animal models, but it's too premature to bet your life on. In researching Stoned, I spoke with a young woman with a very treatable form of lymphoma who gave up chemotherapy and chose cannabis oil instead. She died a few months before the book was published."
"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," Dr Rizack and colleagues conclude.
Physicians should be prepared to field questions from patients.
"Doctors certainly need to be prepared to talk with their patients about medical marijuana. Even if they're in a state where it's not legal, their patients are using it," Dr Casarett said.
He first became interested in this topic when a patient asked him about it. "It turned out that she was using it daily, even though I practice in a state (Pennsylvania) where it's not legal," he said.
But that may soon change. On March 17, Pennsylvania lawmakers in the House of Representatives passed Senate Bill 3, which would legalize medical marijuana in the state.
Dr Casarett also noted that patients do not rely on doctors for advice on marijuana. "They need a doctor to get permission to purchase marijuana legally, but, in my experience, most patients will get advice from dispensaries. So dispensary workers need training, too."
Dr Casarett said that many patients turn to medical marijuana in search of a sense of control. "It's not just medical benefits, although those are real. It's also the ability to tailor your own treatment to meet your needs. People facing serious illnesses like cancer often lose control, and the ability to manage your own symptoms helps some people get a little of that control back," he said.
The study received no funding. The authors have disclosed no relevant financial relationships.
JAMA Oncol. Published online March 17, 2016. Full text
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Cite this: Marijuana for Cancer: No Benefit, but Don't Tell Patients - Medscape - Mar 17, 2016.