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Can cannabis alone cure cancer? We asked oncologist Dr. Donald Abrams

February 4, 2020
Early research on mice has been promising, but no human studies have shown dramatic curative powers. (Mitch/AdobeStock)

Can cannabis alone cure cancer?

The short answer is no. There are as yet no major studies that offer conclusive proof that cannabis alone can cure cancer.

The long answer is more complex.

Researchers are investigating some intriguing anti-carcinogenic effects of cannabinoids like THC and CBD. Pharmaceutical companies have tested cannabinoid medications on patients with aggressive brain tumors with positive but not dramatic results. Some cancer survivors have extolled the curative value of concentrated cannabis oil. Entire books have been written on the subject.

But there may be real risk and potential deadly harm in relying solely on cannabis as a cancer-fighting strategy.


A patient’s guide to using cannabis for cancer

Experts team up to send a clear message

Last week two of the world’s foremost clinicians and researchers in the field of cannabis and cancer, Dr. Donald Abrams and Prof. Manuel Guzmán, published a JAMA Oncology article aimed at clearing up the confusion.

Two of the world's foremost experts published an article aimed at clearing up the confusion.

Abrams is a renowned integrative oncologist, clinician, medical cannabis pioneer, and medical professor at the University of California, San Francisco. Guzmán and his lab at Spain’s Complutense University of Madrid have published a number of groundbreaking studies on cannabis and cancer.

In the article, they acknowledge that “many patients with cancer diagnoses are convinced, mainly by internet testimonials, that cannabis, particularly highly concentrated oils or tinctures of THC and/or CBD, may actually cure their cancers.”

The authors don’t mention it by name, but Rick Simpson Oil (RSO), a highly concentrated cannabis oil, is often mentioned in online cannabis forums as a tool to try in the treatment of cancer.

A proven help with nausea, appetite, pain

Cannabis has long been used by cancer patients—with actual proven efficacy—to manage the side effects of chemotherapy, such as nausea and lack of appetite. It also helps many patients manage cancer pain.

Meanwhile, a number of researchers conducting cell culture studies have published data indicating that THC and other cannabinoids may trigger apoptosis (naturally programmed cell death) in cancer cells.

In a recent interview, Guzmán said this about the state of research on cancer and cannabinoids:

“Practically all the research carried out to date on cannabinoids and cancer cells has used cancer cells cultured on plates or animal models of cancer (generally mice, sometimes rats). Based on numerous scientific studies, various cannabinoids…exercise a wide range of effects that inhibit the growth of cancer cells. These include: (a) Activating cell death through a mechanism known as “apoptosis”. (b) Blocking cell division. (c) Inhibiting the formation of new blood vessels in tumours, in a process known as angiogenesis. (d) Reducing the metastatic capacity of the cancer cells, preventing them from migrating or invading neighboring tissues. To sum up, cannabinoids appear to be effective substances for the experimental treatment of at least some types of cancer, at least in small laboratory animals.”

That’s incredibly promising. But results from cultured cells or mice often fail to carry over to the human body.

‘Disturbing’ use of cannabis alone

The main takeaway from the JAMA Oncology article is this: Treatments like RSO may or may not be beneficial to individual cancer patients, but they should not be used as a substitute for all forms of conventional treatment.

Foregoing conventional therapy “for a curable malignant neoplasm while choosing cannabis as a therapy instead is disturbing,” wrote Abrams and Guzmán.

'One of the most painful things,' says Dr. Abrams, is 'seeing patients who have a potentially curable malignancy who choose to forego conventional cancer treatment.'

In a phone interview from his home in the Bay Area, Abrams told Leafly that he and Guzmán were asked to contribute the article by an editor at JAMA Oncology—indicating that clinical oncologists may be confronting the issue with increasing frequency.

In his own practice, Abrams said he too often encounters patients who have misguidedly abandoned conventional cancer treatment in favor of a cannabis-only regimen.

“As an integrative oncologist, I see patients who often have waited months to get an appointment with me,” he said. “One of the most painful things I have to deal with are people who have a potentially curable malignancy who choose to forego conventional cancer treatment, and instead choose to try to treat themselves with highly concentrated oils with either THC, CBD, or both.”

“They come to me, and by that time they have diseases that have spread and can’t be cured,” Abrams added. “I find that really tragic. They expect me to give them a pat on the back and say ‘Yeah, you’re doing the right thing, continue.’ But now they’ve lost their chance to be cured.”

First research in the 1970s

The first study to show evidence of anti-cancer effect in cannabis came out in 1975. That study, which Abrams mentions in a 2019 article, “Should Oncologists Recommend Cannabis?”, showed that THC and CBD could inhibit the growth of certain lung cancer cells in test tube experiments. Subsequent studies found that cannabinoids selectively killed glioblastoma (brain cancer) cells in mice while leaving normal cells untouched.

But the results from studies on human subjects battling brain cancer have been mixed. One of Guzmán’s own studies looked at the use of THC by nine glioblastoma patients. It found no benefit beyond that observed with chemotherapy alone.

Test tube studies aren’t human studies

While other research has shown early signs of promise with regard to cannabis and cancer cells, Abrams offered some perspective on the gap between lab tests and clinical trials in actual human subjects.

'Taking cells in culture and adding chemicals to them is very different than digesting something in the human body.'
Dr. Donald Abrams, integrative oncologist

“We know there are agents that work against cancer in the test tube that never [become drugs] that we use in fighting cancer, because they just don’t work in people,” he said. “I was an AIDS doctor for many years. We knew that soap suds and gasoline killed the virus in test tubes. But neither of those would be treatments I’d recommend a patient try.”

“Things that happen in vitro don’t necessarily translate into potential clinical benefits,” Abrams continued. “Taking cells in culture and adding chemicals to them is very different than digesting something in the human body. Humans have a digestive system, detoxification systems, and an immune system. All of those things contribute” to the interaction of a drug, the body, and cancer cells. It’s much more complex than what you see in the test tube.”

Bruce Barcott's Bio Image

Bruce Barcott

Leafly Senior Editor Bruce Barcott oversees news, investigations, and feature projects. He is a Guggenheim Fellow and author of Weed the People: The Future of Legal Marijuana in America.

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  • Sam Gamgee

    I’ve watched every person I’ve known that underwent chemo die a fairly slow, incredibly painful death. Personally, if faced with an advanced diagnosis, I’m sparking up a big blunt and gobbling RSO like there’s no tomorrow. At least I’ll go out happy, instead of professionaly poisoned.

  • Rick

    I’m a 40 yr. stoner and I still got prostate cancer. My answer is NO.

    • Sam Gamgee

      If you had been smoking chemo drugs this whole time and still got cancer, would you think chemo wasn’t a valid treatment for cancer?

  • Ned

    The doctor in this article FAILS to take into account ALL of the medical studies done in foreign countries that say the EXACT opposite. I will place my trust in the herbs of the field.

  • Bob

    Cannabis sativa has been used successfully for over two hundred years by homeopaths to treat cancer, of the lip, kidney, and the skin, especially when extremely painful or when caused by overexposure to sunlight (for the facts, see Homeopathic Cancer Drugs, by Manfred Mueller, page 423).
    However to reduce the size of a tumor is one thing, promising, but it is not necessarily a cure. And to show anticancer effect on cancer cell lines is far from a cure. But Cannabis has been proven to be highly effective in reducing cancer pain.

  • Kaabi

    Thank you for writing this article and linking to my book initially, that’s awesome. There are indeed severe limits to cannabis therapy and it doesn’t work for everyone. However, it is also clear based on the overwhelming preclinical, clinical, anecdotal, and logical evidence that it can work profoundly well in some patients. The update of my book at has over 100 human cases and detailed analysis of studies showing how phytocannabinoids and endocannabinoids kill cancer cells through similar mechanisms. The last fact makes it far more likely that high doses of cannabinoids would work in humans, which clearly they are.

  • Howard Paris

    Dr. Donald Abrams answers “No” to the question of whether cannabis cures cancer. That is the worst betrayal of his Hippocratic Oath. The correct answer is: “Yes, for a select minority of cancer types.” While many factors are at play, the evidence of significant efficacy is there. And that level of efficacy has been more than enough to cure many people, even if only anecdotally. The War on Drugs brought research to a standstill in the US and tens of millions died who could have had many more years of life. Moreover, double-blind studies are still a decade or more away. What does Dr. Abrams suggest cancer victims do in the meantime? Chemo? Given the complete lack of toxicity of cannabis and hemp oil, ALL cancer victims should consider combining cannabis/hemp oil with whatever torture the medical community recommends. Within any reasonable time frame, field testing is the only way we’ll learn what cancers can be stopped by cannabis. If the medical community had any balls, they’d publish protocols to help people use cannabis even while illegal.

  • Sam Gamgee

    My point is people tend to hold cannabis to a level of expectation in efficacy and safety that doesn’t get applied to just about anything else. Chemo on average has a moderate success rate. If chemo is the only option. i.e. not localized or no tumor to remove, the success rates are dramatically lower. Even then it needs to be administered in a particular manner. They aren’t smoked, they can’t just be poured over someone. So your claim that smoking it for years didn’t prevent you from getting cancer is a non sequitor. The article explores whether it can be used to treat cancer, which from your statement you didn’t treat your cancer with cannabis, you just happened to smoke it a bunch prior to getting cancer. Regardless, I hope everything goes well, or better yet, went well with your prostate cancer. Even if cannabis didn’t have a preventitive effect for you, hopefully it offers some relief. Either way, we’re just learning about this marvelous little herb after near a century of misinformation. But you’re likely right, smoking it doesn’t look like the right path to unlock all of its health benefits.