You can use cannabis during chemotherapy, but smoking it is the least advisable way to do so, and the decision involves real tradeoffs worth understanding before you light up or eat an edible. Cannabis can help with chemo-related nausea, appetite loss, and discomfort, yet it also carries specific risks: it can interact with chemotherapy drugs through shared liver enzymes, it may reduce the effectiveness of certain immunotherapies, and smoking it introduces lung irritation at a time when your immune system is already compromised.
How Cannabis Helps During Chemo
The most well-supported benefit of cannabis during chemotherapy is nausea control. A systematic review in the BMJ found that cannabinoids were significantly more effective than conventional anti-nausea medications. About 59% of patients using cannabinoids achieved complete control of nausea, compared with 43% on standard drugs. For every six patients treated with cannabinoids instead of conventional options, one additional patient avoided nausea entirely. When the analysis was limited to trials where anti-nausea drugs were moderately effective, the numbers were even more favorable, with fewer than four patients needing treatment for one additional person to benefit.
Appetite stimulation is the other commonly cited benefit. A synthetic version of THC called dronabinol is FDA-approved specifically for appetite loss and chemo-related nausea. In a pilot study of cancer patients, those given THC reported better pre-meal appetite, improved sleep quality, more relaxation, and food that “tasted better” compared to placebo. However, the evidence for actual weight gain is weaker. Larger trials comparing cannabis extracts and THC to placebo have failed to show clear differences in appetite improvement, weight, quality of life, or mood. So while cannabis may make food more appealing, it hasn’t been proven to reverse the muscle and weight loss that often accompanies cancer treatment.
The Drug Interaction Problem
Cannabis compounds are processed by the same liver enzymes that break down many chemotherapy drugs. CBD is the bigger concern here. It strongly inhibits a broad range of these enzymes, meaning it can slow down or speed up how your body processes certain medications. THC also inhibits some of the same pathways, though generally less potently than CBD.
In practical terms, if your liver can’t break down a chemo drug at its normal rate, that drug may accumulate to higher-than-intended levels, increasing side effects. Alternatively, if a drug needs to be activated by the liver, inhibiting that enzyme could make the drug less effective. One reassuring finding: clinical studies showed that cannabis did not meaningfully alter the blood levels of two common chemo agents, irinotecan and docetaxel. But the enzyme overlap is real and broad enough that your oncologist needs to know what you’re using. The specific chemo regimen you’re on matters enormously in determining whether cannabis poses a meaningful interaction risk.
Cannabis and Immunotherapy
If your treatment involves immune checkpoint inhibitors rather than traditional chemotherapy, cannabis use raises a distinct concern. A study of 140 patients with advanced melanoma, lung cancer, or kidney cancer found that those using cannabis alongside the immunotherapy drug nivolumab had a tumor response rate of just 15.9%, compared to 37.5% for patients on nivolumab alone. Cannabis was the only statistically significant factor that reduced response rates in that analysis.
Interestingly, cannabis use did not affect how long patients lived or how long they went without their cancer progressing. The study was retrospective, meaning it looked backward at patient records rather than testing the question in a controlled way, so it can’t prove cannabis caused the lower response. But the signal is strong enough to warrant a conversation with your oncologist, especially if immunotherapy is part of your plan.
Why Smoking Is the Worst Option
Chemotherapy suppresses your immune system, making your lungs more vulnerable to irritation and infection. Smoking cannabis produces many of the same combustion byproducts as smoking tobacco, including compounds that inflame the airways. For patients receiving drugs that carry their own risk of lung damage, such as bleomycin (commonly used for Hodgkin lymphoma), cannabis smoke is an added insult that has been linked in case reports to progressive lung toxicity.
Beyond lung-specific chemo drugs, any patient with a suppressed white blood cell count faces increased risk from inhaling hot, irritating smoke. Airway inflammation can become a pathway for bacterial or fungal infections when your body’s defenses are down. Vaporizing cannabis reduces exposure to some of these harmful combustion byproducts compared to smoking, though it doesn’t eliminate all risk. Edibles, tinctures, and capsules bypass the lungs entirely and are generally considered safer routes during treatment.
Edibles, Capsules, and Prescription Options
If you and your oncologist decide cannabis is worth trying, oral forms avoid the lung risks but come with their own considerations. Edibles take 30 minutes to two hours to kick in, making it harder to control your dose. You may eat more than intended before feeling the first dose. Oral cannabinoids also tend to produce more side effects like dizziness, low blood pressure, and mood changes compared to inhaled forms, partly because the liver converts THC into a more potent metabolite when it’s swallowed.
Three FDA-approved synthetic cannabinoid medications exist specifically for chemo-related nausea: dronabinol (sold as Marinol and Syndros) and nabilone (sold as Cesamet). These offer standardized dosing, which removes the guesswork of dispensary products, and they can be prescribed by your oncologist as part of your anti-nausea regimen. The American Society of Clinical Oncology’s 2024 guideline notes that cannabis or cannabinoids may improve nausea and vomiting that hasn’t responded to standard anti-nausea drugs, but emphasizes that the evidence for other benefits like pain, sleep, or anxiety remains uncertain.
What to Tell Your Oncologist
ASCO’s guideline specifically calls for open, nonjudgmental communication about cannabis use. Your oncologist isn’t going to drop you as a patient for using cannabis, but they need to know about it for the same reason they need to know about every supplement and medication you take. The liver enzyme interactions are real, the immunotherapy data raises legitimate questions, and the form you’re using (smoked, vaped, eaten, or prescribed) changes the risk profile. Many oncologists are comfortable incorporating cannabis into a treatment plan when they know the full picture. The worst approach is using it without telling anyone.
One thing ASCO is clear about: cannabis should not be used as a cancer treatment itself. No reliable evidence supports using cannabis to fight cancer outside of a clinical trial. Its role is in managing symptoms, and in that role, it can be a useful tool when the standard options aren’t enough.