Cannabis does not treat lung cancer, and smoking it is not safe for your lungs, though large studies have not found a clear link between cannabis smoking and lung cancer. THC slowed lung tumors in mice, but no human trial has tested cannabis as a lung cancer treatment. For people with lung cancer, the proven role for cannabinoids is limited to chemotherapy nausea, and smoked cannabis is the worst way to take it.
Lung cancer gets two different questions: can cannabis cause it, and can cannabis treat it. The answers point in opposite directions from what many people expect. This page covers both, based on research available as of October 2026, and is part of our overview of cannabis and cancer.
Evidence at a Glance
| Claim | Evidence level | Source |
|---|---|---|
| Smoking cannabis causes lung cancer | Moderate evidence of no statistical association; heavy long-term use not ruled out | NASEM 2017, Zhang 2015 |
| Cannabis smoke damages the airways | Strong (“substantial”) for cough, phlegm and bronchitis | NASEM 2017, CDC |
| THC shrinks lung tumors | Preclinical only (cells and mice) | Munson 1975, Preet 2011 |
| Cannabis treats lung cancer in people | No human evidence | ASCO 2024 |
| Cannabinoids ease chemotherapy nausea | Strong for refractory nausea | FDA, Cochrane 2015 |
| Cannabis may blunt immunotherapy response | Limited (observational) | Taha 2019 |
Does Smoking Marijuana Cause Lung Cancer?
The best current answer is: probably not in the way tobacco does, but heavy use has not been cleared. Cannabis smoke contains many of the same toxins, irritants and carcinogens as tobacco smoke, according to the CDC, and people tend to inhale it more deeply and hold it longer. Yet the population studies have mostly come back negative.
The Los Angeles case-control study (2006)
The best-known study, led by Mia Hashibe with UCLA pulmonologist Donald Tashkin, compared 611 lung cancer patients and hundreds of people with head and neck cancers against 1,040 cancer-free controls. After adjusting for cigarette smoking and other factors, even heavy cannabis use (60 or more joint-years) was not linked to higher lung cancer risk. A joint-year is one joint a day for a year. The authors cautioned that recall of lifetime use and selection bias could affect the result.
The international pooled analysis (2015)
The International Lung Cancer Consortium pooled six studies from the US, Canada, the UK and New Zealand. Habitual cannabis smokers had no overall increase in risk (odds ratio 0.96). The authors still found a weak upward trend with heavy cumulative use and said an effect at high exposure could not be excluded.
Studies that found a link
Two studies point the other way. A New Zealand case-control study of adults 55 and under found that risk rose 8% for each joint-year, with a 5.7-fold risk in the heaviest users, though it had only 79 cases. A 40-year Swedish cohort of military conscripts found that men who had used cannabis more than 50 times when assessed at conscription, around age 18 to 20, had roughly twice the lung cancer risk, after adjusting for tobacco.
What the reviews conclude
The National Academies found moderate evidence of no statistical association between cannabis smoking and lung cancer. A 2019 JAMA Network Open meta-analysis called the lung findings mixed, mainly because few people smoke only cannabis and exposure was poorly measured. The safest reading: no proven link, but not proof of safety, especially for daily smokers and anyone who also uses tobacco.
Smoking-Related Lung Harms That Are Established
Whatever the cancer data show, smoke harms the lungs. The National Academies found substantial evidence that long-term cannabis smoking causes worse respiratory symptoms and more frequent bronchitis, and that these improve after quitting. The CDC adds that smoking cannabis can scar lung tissue and damage small blood vessels. Mixing cannabis with tobacco, common in spliffs and blunts, adds tobacco’s well-established cancer risk. If you use cannabis, non-smoked forms avoid the smoke; see our guide to using cannabis without smoking and our explainer on vaporizing, which reduces but does not eliminate airway exposure.
Can Cannabis Treat Lung Cancer?
What lab and animal studies show
Lung cancer was the subject of one of the earliest cannabinoid tumor studies. In a 1975 study in the Journal of the National Cancer Institute, researchers found that oral THC slowed the growth of Lewis lung adenocarcinoma in mice and modestly extended survival. Later mouse studies reported that cannabinoids acting on CB1 and CB2 receptors cut non-small cell lung cancer growth and metastasis in mice by about half. NCI’s PDQ summary also describes CBD reducing lung cancer cell invasiveness in the lab.
What human studies show
Nothing that supports treatment. No randomized trial has tested cannabis or cannabinoids as a lung cancer therapy. ASCO’s 2024 guideline advises against using cannabis as a cancer-directed treatment outside a clinical trial.
Cannabis and Lung Cancer Immunotherapy
This matters because immunotherapy drugs such as nivolumab and pembrolizumab are now standard for many lung cancers. In a 2019 Israeli study of 140 patients with advanced cancers, the response rate to nivolumab was 37.5% without cannabis and 15.9% with it. Survival did not differ. A 2020 prospective study of 102 patients starting immunotherapy linked cannabis use to shorter time to progression and shorter survival. Both studies are observational, and sicker patients may be more likely to use cannabis, but cannabinoids do affect the immune system. Tell your oncologist before combining them.
Symptom Relief for People With Lung Cancer
- Nausea and vomiting: The FDA approved dronabinol and nabilone for chemotherapy nausea that does not respond to standard drugs. ASCO supports cannabinoids as an add-on for refractory nausea.
- Pain: A 2023 Cochrane review found that nabiximols and THC did not beat placebo for opioid-resistant cancer pain. It also found low-certainty evidence that nabilone did not reduce pain during chemoradiation in people with head and neck or non-small cell lung cancer.
- Appetite: Trials have been mostly negative; megestrol beat dronabinol for appetite and weight.
- Breathlessness and cough: No good evidence of benefit, and smoked cannabis can make both worse.
Risks and Side Effects
- Smoke irritates already damaged lungs and adds carcinogen exposure.
- CBD inhibits liver enzymes that process many targeted lung cancer drugs and chemotherapy; NCI warns of possible interactions.
- Possible reduced response to immunotherapy (observational evidence).
- Drowsiness, dizziness, low blood pressure and confusion; NIDA also notes the risk of cannabis use disorder with heavy use.
- Mold contamination of smoked cannabis is a concern raised by physicians for people with weakened immune systems.
Talk to Your Doctor
If you have lung cancer, tell your oncologist about any cannabis use, especially before starting immunotherapy or a targeted drug. Ask whether a prescription cannabinoid fits your nausea, and avoid smoking anything. If you are worried about your own risk because you smoke cannabis, tobacco or both, ask whether you qualify for lung cancer screening.
Lung Cancer and Marijuana FAQ
Can smoking weed give you lung cancer?
Large studies have not found a clear link, and the National Academies rated the evidence as moderate for no association. Some studies suggest heavy long-term use may raise risk, and cannabis smoke contains carcinogens, so it is not risk-free.
Is smoking weed worse than cigarettes for your lungs?
Per puff, cannabis smoke delivers similar toxins and is often inhaled more deeply. Most cannabis users smoke far less than cigarette smokers, which may explain why cancer studies look different. Both cause bronchitis symptoms.
Does THC kill lung cancer cells?
In lab dishes and mice, cannabinoids slowed lung tumors. No human study has shown that THC treats lung cancer.
Can I use cannabis during lung cancer immunotherapy?
Talk to your oncologist first. Observational studies have linked cannabis use to lower response rates to nivolumab.
Is vaping cannabis safer for the lungs?
Vaping flower avoids combustion and reduces some toxins, but it is not proven safe. Edibles, capsules and tinctures avoid the lungs entirely.
For adults 21+ in legal states. General information, not medical advice. Talk to a doctor before using cannabis for a health condition.