Cannabis has become one of the most discussed topics in conversations about cancer, wellness, and integrative medicine. Many patients hear testimonials on social media, forums, or support communities claiming that marijuana, cannabis oil, CBD, or THC can “cure” cancer. At the same time, some patients report relief from symptoms such as pain, nausea, anxiety, loss of appetite, or difficulty sleeping. This mixture of personal experiences, legitimate expectations, and exaggerated messages has created an important question: what do we really know about cannabis in the context of cancer?
The answer requires balance. On one hand, there are components of cannabis that have been studied for their potential to relieve symptoms related to the disease or to cancer treatments. On the other hand, to date there is no solid clinical evidence showing that cannabis or cannabinoids can cure cancer in humans. This difference is fundamental: helping with symptoms is not the same as directly treating the tumor.
What are cannabinoids?
Cannabis contains more than one hundred compounds known as cannabinoids. The best known are tetrahydrocannabinol, or THC, and cannabidiol, or CBD. THC is the main psychoactive compound in the plant; that is, it can produce a feeling of euphoria, changes in perception, drowsiness, or changes in mood. CBD, in contrast, does not produce the same classic psychoactive effect, although it can have important biological actions and can also interact with medications.
The human body has a system called the endocannabinoid system, made up of molecules produced by the body and cellular receptors that participate in processes such as pain, appetite, inflammation, immune response, sleep, and stress regulation. Two important receptors are CB1 and CB2. CB1 is found mainly in the nervous system, while CB2 is present in several cells of the immune system. For this reason, cannabinoids can influence not only neurological or digestive symptoms, but also immune functions.
This point is especially relevant in cancer. In modern oncology, many therapies seek to activate or restore the ability of the immune system to recognize and attack tumor cells. If a substance modifies the immune response, it needs to be studied carefully, especially when the patient is receiving immunotherapy.
Cannabis for symptoms: what has more support
The most accepted use of cannabinoids in oncology is related to symptom management. Some cannabinoid products have shown usefulness for chemotherapy-induced nausea and vomiting, especially when these symptoms do not improve adequately with standard antiemetic medications. There are also patients who report improvement in appetite, sleep, pain, or anxiety, although the quality of the evidence varies depending on the symptom, the product used, the dose, and the route of administration.
However, cannabis is not a universal solution. Two people may respond very differently to the same product. The concentration of THC and CBD can vary widely among oils, edibles, vaporizers, dried flower, and artisanal preparations. In addition, many commercial products do not have the same quality control as an approved medication. This can lead to problems with dosage, contamination, unexpected effects, or interactions with other treatments.
For this reason, any use of cannabis during cancer should be discussed with the medical team. It is not only a matter of asking whether it is “natural” or whether it “helps with sleep.” It is also necessary to consider the type of cancer, the current treatment, liver function, bleeding risk, concomitant medications, age, neurological status, and the risk of falls or confusion.
Can cannabis directly treat cancer?
This is one of the most delicate questions. In laboratory studies, some cannabinoids have shown effects on important processes in cancer cells, such as proliferation, meaning the ability to multiply; apoptosis, a natural and programmed form of cell death; inflammation, which can influence tumor growth and its interaction with the immune system; angiogenesis, which is the formation of new blood vessels that can feed the tumor; and cell survival signals, which are internal mechanisms that help tumor cells resist damage and continue living. There are also animal studies suggesting possible antitumor effects under specific conditions. However, although these findings are scientifically interesting and deserve further investigation, they still do not show that cannabis or cannabinoids can cure cancer in humans.
Preclinical studies are not the same as a proven therapy in patients. Many substances can reduce the growth of tumor cells in a laboratory dish or in animal models and still not work in humans, or not be safe at the required doses. Cancer is a complex disease: the tumor microenvironment, the immune system, tumor genetics, previous treatments, and the patient’s general condition all influence response.
For now, the main clinical guidelines recommend not using cannabis or cannabinoids as a cancer-directed treatment outside of a clinical trial. This recommendation does not deny the scientific interest of the topic; it simply recognizes that there is still not enough evidence to consider it a standard antitumor therapy.
Cannabis and immunotherapy: a current concern
One of the most important topics today is the possible interaction between cannabis and immunotherapy. Immunotherapies, such as immune checkpoint inhibitors, work by stimulating or unlocking the immune response against the tumor. If cannabinoids have immunomodulatory effects, there is a possibility that they could interfere with some mechanisms needed for immunotherapy to work properly.
A study in patients treated with nivolumab, an anti-PD-1 immunotherapy, in which concomitant cannabis use was associated with a lower tumor response rate. This type of finding does not definitively prove that cannabis causes a worse response, because observational studies may have confounding factors. For example, patients who use cannabis may have more pain, more symptoms, more advanced disease, or poorer general condition. Even so, the signal is important enough to justify caution.
Later studies have attempted to evaluate this possible interaction in other contexts, with results that are not always the same. Some data have suggested lower response or survival in certain groups, while other studies do not find such a clear effect. The responsible conclusion is that there is still no definitive answer, but there is a scientific reason to talk with the oncologist before using cannabis during immunotherapy.
Figure 1. Cannabis products may support selected symptoms, but their effects vary by patient, product type, dose, and treatment context. Medical guidance is especially important during active cancer therapy, including immunotherapy.
The problem of misinformation
One of the greatest difficulties for patients is distinguishing between scientific evidence and commercial promises. The internet is full of claims such as “cannabis oil cures cancer,” “THC eliminates tumors,” or “conventional medicine hides the cure.” These types of messages can be dangerous, especially if they lead a person to delay surgery, chemotherapy, radiotherapy, immunotherapy, or targeted treatments that do have clinical evidence.
It is also common for individual testimonials to be used as proof. Although personal experiences can be valuable from a human point of view, they do not make it possible to know whether a patient improved because of cannabis, another treatment, the natural biology of their tumor, or a combination of factors. In oncology, to know whether an intervention works, well-designed clinical studies are needed, with comparison groups, adequate follow-up, and objective response criteria.
Hope is important, but it must be accompanied by clear information. A patient can explore supportive options, integrative medicine, or symptom control without abandoning effective treatments or exposing themselves to unsafe products.
Safety: not all products are the same
Cannabis can cause adverse effects. Products with THC can produce drowsiness, anxiety, paranoia, dizziness, memory changes, tachycardia, or coordination problems. In older or weakened individuals, this can increase the risk of falls. In some patients, especially those with psychiatric history, it can worsen anxiety, confusion, or psychotic symptoms.
CBD also requires caution. Although it is often promoted as “harmless,” it can affect liver enzymes that metabolize medications. This means it could modify the levels of some drugs in the blood, increasing toxicity or reducing efficacy. In oncology patients, who frequently receive multiple medications, this possibility must be carefully evaluated.
Another problem is product quality. Some preparations may contain amounts of THC or CBD different from those indicated on the label, pesticides, heavy metals, residual solvents, or microbiological contaminants. Inhaled products can also irritate the respiratory system, which is relevant in patients with lung cancer, previous lung disease, or immunosuppression.
A balanced position for patients and families
Cannabis should not be presented as a cure for cancer. That claim is not supported by solid clinical evidence. However, it should also not be ignored that some patients may experience symptom relief when it is used responsibly, under supervision, and within an integrated care plan.
The best strategy is to speak openly with the medical team. Many patients do not mention cannabis use for fear of being judged, but hiding it can be risky. The oncologist needs to know what products the patient uses, at what dose, how often, and by which route, especially if the patient is receiving immunotherapy, anticoagulants, sedatives, opioid analgesics, antiepileptic drugs, liver-related treatments, or medications with a high risk of interaction.
Modern medicine is not based on rejecting questions, but on answering them with evidence. Cannabis and cancer is an active field of research, but it still needs stronger clinical trials, better standardized products, long-term follow-up, and studies that clearly differentiate between symptom relief and antitumor effect.
Important note: Patients with cancer should not start, stop, or combine cannabis products with cancer treatments without first consulting their medical team. This is especially important for patients receiving immunotherapy, chemotherapy, anticoagulants, sedatives, or other medications with a risk of interaction.
Main reference
Braun, I. M., Bohlke, K., Abrams, D. I., Anderson, H., Balneaves, L. G., Bar-Sela, G., Bowles, D. W., Chai, P. R., Damani, A., Gupta, A., Hallmeyer, S., Subbiah, I. M., Twelves, C., Wallace, M. S., & Roeland, E. J. (2024). Cannabis and Cannabinoids in Adults With Cancer: ASCO Guideline. Journal of clinical oncology : official journal of the American Society of Clinical Oncology, 42(13), 1575–1593. https://doi.org/10.1200/JCO.23.02596
Other references:
Taha, T., Meiri, D., Talhamy, S., Wollner, M., Peer, A., & Bar-Sela, G. (2019). Cannabis Impacts Tumor Response Rate to Nivolumab in Patients with Advanced Malignancies. The oncologist, 24(4), 549–554. https://doi.org/10.1634/theoncologist.2018-0383
Waissengrin, B., Leshem, Y., Taya, M., Meiri, D., Merimsky, O., Shamai, S., Wolf, I., & Rubinek, T. (2023). The use of medical cannabis concomitantly with immune checkpoint inhibitors in non-small cell lung cancer: A sigh of relief?. European journal of cancer (Oxford, England : 1990), 180, 52–61. https://doi.org/10.1016/j.ejca.2022.11.022
