Cannabis has become a frequent topic in my clinic—and for good reason. Many of my patients are using it, whether through legal medical marijuana programs, over-the-counter CBD products, or something shared by a neighbor or friend. It’s part of the everyday reality of cancer care in 2025, and we need to talk about it openly and honestly.
Where Cannabis Helps: Symptom Management During Chemotherapy
From my own clinical experience, I’ve seen clear benefits of cannabis for patients going through chemotherapy. Many struggle with chemotherapy-induced nausea and vomiting (CINV), pain, insomnia, and appetite loss—symptoms that can make an already difficult journey even harder.
One patient I recently saw who was receiving chemotherapy for advanced pancreas cancer. Despite our best anti-nausea medications, she was still struggling to keep food down and was rapidly losing weight. At her daughter’s urging, she tried a medical cannabis product. Within a week, her nausea eased, her appetite improved, and she was able to tolerate her treatment better. Maria felt more in control—and more like herself.
Stories like hers are not uncommon. When used judiciously, cannabis can improve quality of life for cancer patients, especially those dealing with the harsh side effects of chemotherapy. Ensure to follow state guidelines and regulations. In Florida, where I practice, I often refer patients to licensed medical marijuana clinics for further guidance on product choice, dosing, and safety.
Where Cannabis May Harm: Immunotherapy and Potential Risks
However, cannabis is not without risks, and one area of concern is its use during immunotherapy—a cornerstone treatment for many cancers today.
Although research is still emerging, two small studies published within an ASCO review article suggest that cannabis might blunt the effectiveness of immune checkpoint inhibitors:
- In a prospective observational study of 102 patients with advanced cancer receiving immune checkpoint inhibitors, those who also used cannabis had a shorter time to disease progression (3.4 months vs. 13.1 months) and shorter median overall survival (6.4 months vs. 28.5 months).
- Another retrospective study of 140 patients showed lower treatment response rates in those using cannabis (19% vs. 37.5%), though there was no significant difference in progression-free survival or overall survival.
These are small studies, and the data is far from definitive. But the possibility of harm—especially when we know that other medications like antibiotics can similarly reduce immunotherapy effectiveness—leads me to counsel caution. Until we have stronger evidence, I advise patients to avoid cannabis use during immunotherapy, particularly in the early months when immune activation is most critical.
What About Cannabis as a Cancer Treatment?
I also frequently hear patients ask whether cannabis can treat cancer itself. The answer, for now, is no. Despite some laboratory studies suggesting anti-cancer effects in cell lines, we have no clinical evidence that cannabis or cannabinoids shrink tumors or improve survival in humans.
In fact, when used in high doses in the hope of “treating cancer,” cannabis could potentially cause harm—through interactions with treatments, worsening cognitive function, or other toxicities. This is especially true for older adults, who may be more vulnerable to side effects like dizziness, confusion, and increased fall risk.
Alcohol vs. Cannabis: A Quick Perspective
I’m often struck by the fact that alcohol—an established carcinogen—remains widely accepted and socially promoted, while cannabis, which has not been definitively linked to cancer risk, still carries social stigma. While I’m not advocating for recreational use, I do think it’s time to have balanced, evidence-driven conversations about both substances.
As for me, I’ve come to terms with my one remaining vice—and the known risks that come with enjoying a neat single malt scotch from time to time.
Key Takeaways for Patients and Families
- Cannabis may help with chemotherapy-related side effects such as nausea, vomiting, pain, insomnia, and appetite loss. Medical marijuana programs can provide safe, regulated options.
- Cannabis should be avoided during immunotherapy when possible, due to potential interference with treatment effectiveness, though more research is needed.
- Cannabis is not a proven cancer treatment—patients should be cautious about claims suggesting otherwise.
- Potential toxicities exist, especially in older adults, including cognitive changes, sedation, and fall risk.
- Open, nonjudgmental conversations with your oncology team are key. We can help you weigh the risks and benefits and guide you toward safe use when appropriate.
I’m encouraged to see organizations like ASCO providing formal guidelines and patient education resources on cannabis use in oncology, helping clinicians and patients navigate this evolving landscape. You can find the latest ASCO guidance.
We still have much to learn. But by staying informed, open-minded, and evidence-driven, we can ensure that cannabis—like every other tool in oncology—serves the ultimate goal: helping our patients live longer, better lives.
About the author
Dr. Sajeve Thomas is a distinguished medical professional and a compassionate guide in the field of oncology. With over a decade of dedicated experience as a board-certified medical oncologist/internal medicine specialist, Dr. Thomas has become a trusted expert in the treatment of melanoma, sarcoma, and gastrointestinal conditions. He brings a wealth of expertise to the complex and challenging world of oncology.
Disclosures:
Dr. Thomas serves as a speaker for Bristol Myers Squibb (BMS), Merck, Ipsen, Natera, Immunocore, Pfizer, and SpringWorks. He also receives industry grants in support of numerous clinical trials.