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Cannabis oil is often heralded as a treatment for cancer and other diseases, but there’s no science to support these claims.
The internet is full of “miracle cures” for cancer and alleged surefire ways to prevent it, and well-meaning people may urge cancer patients to just try them out in hopes of eliminating their disease. Some patients, worried that conventional treatments won’t work or pose significant side effects, seek a treatment whose effectiveness isn’t actually supported by scientific evidence or may even prove dangerous. During a time of uncertainty and anxiety, it’s understandable that any hope for a cure — even if it isn’t medically proven — is tempting.
“Amid the growing preference for natural products to bolster general health, patients often confront a myriad of misinformation,” explains Jason Hou, a pharmacist and herbalist at Memorial Sloan Kettering. “Despite this, they seek natural remedies to combat or prevent cancer recurrence. Often, advocates of such products lack medical or oncological expertise.” Dr. Hou is especially concerned when patients delay conventional treatment to explore such therapies. “They may later don’t discover, when they do seek out conventional treatment, that their cancer has already metastasized.”
Dr. Hou manages both the About Herbs database, and the Herbal Oncology Program (HOP), created and maintained by MSK’s Integrative Medicine Service. The service provides complementary therapies such as acupuncture, music therapy, and massage that are used in addition to — not as alternatives to — standard cancer treatments including chemotherapy, radiation, and surgery.
Here, Dr. Hou explains the hype and the scientific evidence surrounding four highly publicized but unproven therapies: Cannabis oil, castor oil, Laetrile, and a pH-manipulation (also known as alkaline) diet.
The hype: Cannabis oil is often heralded as a treatment to destroy or shrink cancerous tumors, as well as a cure for diabetes, ulcers, arthritis, migraines, insomnia, infections, and many other diseases. Also called marijuana oil or hemp oil, it’s extracted from marijuana plants, often with higher proportion of a compound known as CBD (cannabidiol), which has less of a psychoactive effect than the more-famous THC (tetrahydrocannabinol) compound that gets marijuana users high.
Cannabis oil is available in several forms with different potencies. It can be infused into cooking oil that users squirt under the tongue or mix into food. Its vapors can also be inhaled. By federal law, cannabis products are illegal, though several states have enacted laws to legalize their medical use.
The evidence: While commercially available cannabis compounds are FDA-approved to reduce cancer treatment–related side effects such as nausea and vomiting and to improve appetite, no clinical trials have shown that cannabis products can treat cancer.
Claims that cannabis oil cures cancer are anecdotal and largely unsupportable, based on scant research done in mice and in labs. Side effects can include memory and attention loss. Perhaps most important, there is evidence that cannabis compounds may inhibit enzymes that patients need to metabolize other anticancer drugs, thereby increasing their toxicity or reducing their effectiveness.
The verdict: “Thus far, there haven’t been any human studies demonstrating that cannabis oil can effectively treat cancer,” Dr. Hou explains. “If patients are using it, or any other form of cannabis, it’s important to inform their doctors so they can provide appropriate guidance.” According to a 2024 American Society of Clinical Oncology (ASCO) guideline, “Clinicians should recommend against using cannabis or cannabinoids as a cancer-directed treatment unless within the context of a clinical trial.”
The hype: Castor oil has been recently promoted as a cancer cure over the Internet and social media, particularly on TikTok with claims that it can treat breast cancer by topical application. Recently, we began receiving requests for information about the benefits of castor oil.
The evidence: There is no evidence that castor oil can fight cancer. This underscores the importance of About Herbs in providing trustworthy information while helping to debunk false claims, especially given how easily they get shared and amplified on social media.
The verdict: “We consistently warn patients that ‘natural doesn’t always mean safe.” Dr. Hou explains. “But with social media emerging as a means of disseminating information, we should add that videos that go viral, should not always be trusted!”
The hype: Laetrile, first popularized as a cancer therapy in Russia and the United States more than a century ago, is the trade name for a purified form of amygdalin, an extract derived from apricot pits and some nuts and plants. Intestinal enzymes break down Laetrile to produce cyanide, which proponents claim kills cancer cells and leaves normal tissue unharmed. Some also claim that Laetrile is actually a vitamin called B-17 and that deficiencies can cause certain cancers. Banned in the United States, an oral form of Laetrile is available in other countries.
The evidence: Laetrile indeed breaks down into cyanide, but the poison doesn’t just selectively strike cancer cells — it can sicken or kill patients as well. Clinical studies done in the 1970s and 1980s, including those sponsored by the National Institutes of Health, indicated that Laetrile didn’t reduce malignant tumors’ size or growth, but some patients experienced cyanide poisoning.
The verdict: “Laetrile hasn’t been shown to combat cancer and can pose the risk of cyanide poisoning,” Dr. Hou emphasizes. “If amygdalin is ever considered for use in an anticancer medication, it would need to be in a modified form, as the oral version is toxic to normal human cells and too hazardous for use.”
The hype: Based on the scientific observation that cancer cells thrive in an acidic environment — meaning low pH levels — some people contend that highly “acidic” foods such as meat, cheese, and grain products raise the risk of cancer by reducing pH levels in the blood. They claim that eating “alkaline” foods such as fruit, green vegetables, and other plant-based products discourages the growth of cancer cells by raising blood pH levels and tout the benefits of the alkaline diet (also known as the alkaline ash diet or alkaline acid diet).
The evidence: Cancer cells create an acidic microenvironment due to a high metabolic rate. Cancer cells can’t live in a highly alkaline environment, but neither can healthy cells. Your body works to keep pH levels constant, and changing your diet is not going to substantially change the pH levels of your blood, which are tightly regulated by the kidneys and lungs regardless of foods consumed.
The pH of bodily fluids, such as saliva and urine, does change temporarily depending on the foods you eat, but that doesn’t affect blood pH levels (or, hence, the environment of cancer cells in the body). In fact, any significant deviation in blood pH levels can cause serious, even life-threatening conditions known as acidosis (low pH) or alkalosis (high pH)
The verdict: “There is no evidence to support the notion that altering your diet can alter blood pH levels, let alone impact cancer growth,” Dr. Hou states. “The science behind this has been misconstrued. Modifying the pH of your saliva doesn’t influence the pH of your blood. Some patients may attempt to adjust their blood pH using chemicals, but this can pose serious risks.”
“Natural” cancer therapies should be regarded with great caution because most are unsupported by evidence. Many people offering testimonials to the effectiveness of such treatments may attribute benefits to them simply because their condition improved after using them — when the actual cause for the improvement is unrelated.
The good news is that mainstream cancer therapies are safer and more effective than ever. New chemotherapies work better with fewer side effects, and novel drugs target specific mutations in cancer cells to minimize harm to healthy cells. Highly precise forms of radiation therapy destroy tumors while sparing normal tissue. New approaches harness the body’s own immune powers to destroy cancer cells. And new surgical techniques are making it possible to remove tumors more safely while minimizing both risk of recurrence and recovery times.
If you’re considering using a complementary therapy in addition to your traditional cancer treatments, always check with a reputable source such as our About Herbs database or the National Cancer Institute, and always tell your doctor.
The Truth Behind Four Natural Cancer “Cures” – On Cancer – Memorial Sloan Kettering
