Cannabis and Cancer: What the Research Says (2026)

By James Buddsey · Updated October 30, 2026

Cannabis does not cure cancer, and no cannabis product is approved to treat any cancer. Lab and animal studies show that cannabinoids can kill or slow some cancer cells, but these results have not held up in human trials. The best human evidence supports cannabinoids for one thing: chemotherapy nausea and vomiting that standard drugs have not controlled.

Cancer is the topic where cannabis claims do the most harm. Patients read that THC “shrinks tumors” or that a concentrated oil cured someone’s cancer, and some delay treatment that works. This page sums up what the research actually shows as of October 16, 2026. It draws on the National Cancer Institute’s PDQ summary on cannabis and cannabinoids, the 2024 ASCO guideline on cannabis in adults with cancer, the 2017 National Academies report and Cochrane reviews. It links to our detailed pages on breast, lung, leukemia, pancreatic, colon, oral and brain tumor research.

Evidence at a Glance

Does Cannabis Cure Cancer?

No. There is no human evidence that cannabis, THC, CBD or any cannabis oil cures cancer or extends survival. The National Academies concluded in 2017 that there was insufficient evidence to say whether cannabinoids are an effective treatment for any cancer, including glioma. ASCO’s 2024 guideline goes further: clinicians should recommend against using cannabis or cannabinoids as a cancer-directed treatment unless it is part of a clinical trial.

The FDA has approved cannabinoid drugs only for symptoms, never for the cancer itself. It has also sent warning letters to companies selling CBD products with claims that they treat cancer. The NCI notes that highly concentrated THC or CBD oils promoted as cancer cures have not been tested in clinical trials for either anticancer activity or safety.

Lab and Animal Studies vs. Human Evidence

Most of the headlines come from preclinical research, meaning cells in a dish or tumors grown in mice and rats. That work is real and goes back decades. A 1975 study in the Journal of the National Cancer Institute found that oral THC slowed the growth of lung tumors in mice. Since then, researchers have reported that cannabinoids can trigger cancer cell death, block blood vessel growth into tumors and reduce spread in models of breast, lung, pancreatic, colon, brain and blood cancers. A 2012 Nature Reviews Cancer review lays out the proposed mechanisms.

Three cautions apply to every one of these studies:

• Doses are often far higher than a person could reach by smoking or eating cannabis, and some are injected straight into the tumor.
• Results are not consistent. The NCI notes that in mouse models with a working immune system, THC suppressed antitumor immunity and enhanced tumor growth.
• Most cancer drugs that work in mice fail in people. A positive animal result is a reason to run a human trial, not a reason to use a product.

The Few Human Trials

Human trials of cannabinoids against cancer are small and mostly in brain tumors. A 2006 Spanish pilot study injected THC directly into the tumors of nine patients with recurrent glioblastoma. It was safe, but median survival was 24 weeks and there was no control group. A 2021 UK phase 1b trial gave nabiximols (a THC and CBD mouth spray) or placebo with the chemotherapy drug temozolomide to 21 randomized patients. One-year survival was 83% with nabiximols and 44% with placebo, but the trial was designed to test safety and was too small to prove a survival benefit. Our guide to cannabis and tumors covers this in detail.

What Cannabis Can Help With: Symptoms

This is where the evidence is useful. NCI’s PDQ summary cites a survey of more than 13,000 patients at 12 NCI-designated cancer centers in which about a third reported using cannabis since diagnosis, mostly for pain, sleep, nausea and appetite. Here is how those uses hold up.

Nausea and vomiting from chemotherapy

The strongest evidence. The FDA approved dronabinol (Marinol, and later the oral solution Syndros) and nabilone (Cesamet) for chemotherapy nausea and vomiting in patients who have not responded to standard antiemetics. A 2015 Cochrane review found cannabis-based medicines may help refractory nausea, though the trials are old and predate modern drugs. A 2020 Australian randomized trial found that adding an oral THC:CBD extract to standard antiemetics raised the complete response rate from 14% to 25%, with more sedation and dizziness. ASCO says cannabinoids may help refractory nausea when added to guideline-based antiemetics, not instead of them.

Appetite and weight loss

Weak. In a 469-patient trial, the prescription drug megestrol improved appetite in 75% of patients versus 49% for dronabinol. A 243-patient phase III trial found no difference in appetite or quality of life between cannabis extract, THC and placebo. ASCO calls the evidence for appetite uncertain.

Cancer pain

Disappointing so far. Cannabis has substantial evidence for chronic pain in general, according to the National Academies, but cancer pain trials are a different story. A 2023 Cochrane review of 14 studies found moderate-certainty evidence that nabiximols and THC did not relieve opioid-resistant cancer pain better than placebo. A 2020 meta-analysis reached the same conclusion and found more sleepiness and dizziness with cannabinoids.

Sleep and anxiety

Patients often report better sleep and less anxiety, but NCI describes the clinical evidence as limited to small studies. ASCO found it insufficient to make a recommendation.

Newest research: the October 2026 Penn State survey

A survey published October 9, 2026 in Supportive Care in Cancer surveyed 186 patients at the Penn State Cancer Institute between June 2023 and June 2024 about cannabis; 26.1% had used it since diagnosis. Read more: Cancer Patients Say Cannabis Helps Sleep, Appetite and Pain. Among users, most said it improved insomnia (89.7%), appetite (85.7%), mood (83.7%) and cancer pain (80.7%), and 30.1% said they used cannabis instead of opioids for pain. Evidence level: low. This was a small, self-reported survey of roughly 46 to 48 users with no control group, so it shows what patients believe helps, not what cannabis does, and it does not outweigh the negative appetite and cancer pain trials above. If you are using cannabis or thinking about it, tell your oncologist, especially before cutting back on prescribed medicines.

Does Smoking Cannabis Cause Cancer?

The research is reassuring but not a clean bill of health. The National Academies found moderate evidence of no statistical association between smoking cannabis and lung cancer, and moderate evidence of no association with head and neck cancers. A 2019 JAMA Network Open meta-analysis agreed, but found low-strength evidence linking long-term use to a type of testicular cancer (nonseminoma germ cell tumors). The CDC notes that cannabis smoke contains many of the same toxins and carcinogens as tobacco smoke and can damage lung tissue. Our pages on lung cancer and oral cancer cover the risk studies.

Research by Cancer Type

Risks and Side Effects for People With Cancer

• Delaying real treatment. The biggest risk. No cannabis product replaces surgery, chemotherapy, radiation or immunotherapy.
• Drug interactions. CBD inhibits liver enzymes (cytochrome P450) that break down many drugs. NCI warns that concentrated CBD oils could raise chemotherapy toxicity or reduce its effect.
• Immunotherapy. In a 2019 Israeli study of 140 patients on nivolumab, response rates were 37.5% without cannabis and 15.9% with it, though survival did not differ. A 2020 prospective study of 102 patients linked cannabis use to shorter time to progression and survival. Both are observational, but they are a reason to tell your oncologist.
• Common side effects. Drowsiness, dizziness, confusion, fast heart rate, low blood pressure and anxiety. NIDA lists impaired memory and coordination and, with heavy use, psychosis and cannabis use disorder.
• Smoke. Inhaled smoke irritates airways. The American Cancer Society notes that doctors who recommend cannabis generally prefer forms other than smoking. See our guide to using cannabis without smoking.
• Product quality. Dispensary and online products vary in actual THC and CBD content. Prescription cannabinoids have consistent doses.

Talk to Your Doctor

ASCO’s guideline asks oncologists to discuss cannabis openly and without judgment, so bring it up. Tell your care team what you use, how much and how often, and ask:

• Could cannabis or CBD interact with my chemotherapy, targeted therapy or immunotherapy?
• Would a prescription cannabinoid such as dronabinol or nabilone fit my nausea better than a dispensary product?
• Are there clinical trials I qualify for? NCI keeps a searchable trial database.

Washington and Oregon both include cancer among the qualifying conditions for their medical cannabis programs. See our Washington and Oregon law guides, and the cannabis research hub for other conditions.

Cannabis and Cancer FAQ

For adults 21+ in legal states. General information, not medical advice. Talk to a doctor before using cannabis for a health condition.