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Study: Cannabis use among breast cancer patients

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At a glance What does this mean for me?
Background Clinical trials
Study findings Guidelines
Strengths and limitations Questions for your doctor
Context Resources



What is this study about?

This study is about understanding why and how patients with breast cancer use marijuana (cannabis) to help manage treatment symptoms and side effects. 

Why is this study important?

Advances in breast cancer treatment have significantly reduced the risk of dying from the disease. However, most patients experience treatment symptoms and side effects that impact their quality of life.  This study looked at why breast cancer patients use cannabis.  It is important to know that this study did not gauge the effectiveness of cannabis for relieving treatment symptoms and side effects.


The most studied active ingredients in cannabis are THC and CBD. THC has been more widely studied, and research supports its use for pain and nausea. The has approved two drugs, dronabinol (contains man-made THC) and nabilone (contains synthetic THC) for chemotherapy-induced nausea and vomiting. Other studies support the use of THC for insomnia and anxiety.

Much less research has focused on using CBD to relieve pain, anxiety or sleep issues. Some studies have shown that CBD reduces chemotherapy-induced neural pain in rodents, but this has not been studied in humans. Several studies have shown that CBD reduces anxiety in patients with social phobias; however, this study did not include other diagnoses. The effect of CBD on sleep remains unknown.

Results of studies on the use of cannabis by cancer patients vary considerably. However, all of the studies have found that pain, anxiety and nausea are the most common reasons patients use cannabis. Having cancer is considered a medically qualifying condition in nearly all states that have approved the use of medical cannabis. However, many healthcare providers feel they lack the knowledge needed to discuss cannabis use with their patients. A national survey reported that 70 percent of oncologists did not feel prepared to discuss cannabis use or make clinical recommendations for their patients.

Researchers conducted a study on cannabis use among breast cancer patients to help healthcare providers have meaningful discussions on the subject with their patients. The researchers then presented their results in the context of what is currently known about the risk and benefits of cannabis.

Researchers of this study wanted to know

Researchers wanted to understand why breast cancer patients used cannabis, when they used it, what resources they used to get information about cannabis and the sources they used to obtain cannabis . They also wanted to know how satisfied patients were with the information they received, their perception of the safety of cannabis and whether they talked to their healthcare providers about using cannabis.

Populations looked at in this study

Between December 2019 and January 2020, members of and in the United States were invited to participate in a survey of cannabis use among breast cancer patients who had been diagnosed in the past five years. Participants represented most states except for Montana, North and South Dakota and Mississippi. They were asked to answer 47 questions about their cannabis use, provide information including their age and gender, where they lived, the time since their diagnosis,  the hormone and status and of their cancer, and their current treatment status. Eligibility requirements were met by 612 patients who completed an anonymous online survey. On average, participants were 57 years old, female (99%) and were either in treatment after surgery (46%) or had finished treatment (27%). Information on racial or ethnic demographics was not collected.

Study findings

Interest and use of cannabis

Participants were asked about their level of interest in cannabis use:

  • 64% were very interested or extremely interested.
  • 23% were somewhat interested.
  • 13% were minimally interested or not interested.

 Among the participants who used cannabis:

  • 75% reported that cannabis was extremely helpful or very helpful in relieving symptoms.
    57% said that they found no other way of treating their symptoms.
  • 42% said that they used cannabis for relief of treatment side effects, including pain, insomnia, anxiety, stress and nausea.
  • 79% used cannabis during the time they were undergoing treatment.
  • 49% thought that cannabis could be used to treat their cancer.
  • 39% talked to a healthcare provider about using cannabis.
  • 77% said they used cannabis for both medical and recreational purposes.
  • 70% thought cannabis was safe to use and were not aware that cannabis quality varies widely and is dependent on the source.

Information on cannabis

Half of the participants had looked for information on medical cannabis. According to patients, the most helpful sources of information included:

  • websites (22%)
  • family members or friends (18%)
  • non-pharmacist dispensary staff such as a budtender (12%). (A budtender is someone who helps customers at a dispensary that sells marijuana.)
  • dispensary pharmacist (12%)
  • other patients with breast cancer (7%)
  • non-physician or non-nurse healthcare provider such as a chiropractor (6%)
  • physician (4%)
  • movies or documentaries (3%)
  • nurse (2%)
  • co-worker or colleague (2%)
  • advertisements (1%)

Of those who sought information on the use of cannabis for medical purposes, most were only somewhat satisfied or unsatisfied with the information they received.

Reasons for cannabis use

Participants who used cannabis reported using it for:

  • relieving pain (78%), including acute and chronic joint and muscle aches, discomfort, stiffness or nerve pain.
  • insomnia (70%).
  • anxiety (57%).
  • managing stress (51%).
  • nausea/vomiting (46%).

Among cannabis users:

  • 75% reported that it was extremely helpful at relieving their symptoms.
  • 57% reported that they found no other way to relieve their symptoms.

Cannabis use during treatment

Among participants who reported that they used cannabis:

  • 24% reported that they used it before active treatment started,
  • 79% reported that they used it during treatment
  • 54% reported they used it after completing treatment.

Almost half (49%) of patients who reported using cannabis said that one reason they did so was to treat their cancer (beyond trying to manage treatment side effects). (Note: No documented evidence supports the use of cannabis to treat cancer.)

Sources of cannabis

Participants reported that they used various forms of cannabis, including edibles, liquids/tinctures, topicals, smoking and vaping. Most reported that they obtained cannabis from:

  • medical dispensaries (54%).
  • family or friends (33%).
  • Recreational/adult-use dispensaries (27%). 

Fewer participants reported obtaining cannabis from other sources:

  • dealer (6%)
  • delivery service (5%)
  • grew their own (5%)
  • drug store (4%)
  • online dispensary (4%).

Most participants preferred CBD to THC: 22% preferred CBD only, 21% preferred mostly CBD and 19% preferred an equal ratio of CBD to THC. Only 26% of participants preferred THC-only products, while 7% reported no preference. However, many participants reported that they did not understand the difference between CBD and THC or the difference between CBD and THC that are derived from hemp compared to marijuana products.

The perceived safety of cannabis use

 Most participants thought that cannabis should be viewed as a plant-based medicine, that natural products were better than “chemicals,” and that the benefits of using cannabis outweighed the risks. When asked about the differences between medical and recreational cannabis use, 79% believed that medical cannabis was more “clean/pure.” Most (64%) thought medical cannabis was safer than recreational cannabis, while some (35%) thought there was no difference.


While study participants reported using cannabis for a range of symptoms, they also reported using a wide range of THC and CBD products. While THC has been shown to relieve these symptoms, the effect of CBD on these symptoms is currently unknown.

Preclinical studies have shown that THC and CBD reduce tumor growth and in animal models. Whether this is also true for humans is unknown. The impact of cannabis on breast cancer treatment and outcomes also remains unknown.

Strengths and limitations


  • This study was able to capture a national sample of breast cancer patients in all age groups who were undergoing or had had a range of treatments.


  • Like all survey studies, a major limitation is selection biases.  It is possible that there was overrepresentation of patients who regularly used cannabis for recreation, had more side effects due to more aggressive treatment for advanced disease or live states where cannabis is legal. Because of these limitations, this study likely does not represent most breast cancer patients.
  • Limitations also include the possibility that cannabis use was under reported by participants due to its illegal (federal and some states) status and social stigma.

What does this mean for me?

Among breast cancer patients, there is a strong interest in medical cannibis. Currently, 36 states and four territories allow for the medical use of cannabis products to help manage treatment side effects of cancer or other medical conditions. The safest sources of cannabis products are state-approved medical dispensaries. However, these are not available to all patients, and many dispensaries require patients to obtain their healthcare provider’s certification that they can use cannabis. The price of medical cannabis is usually higher compared to other sources (including recreational or illegal sources); this may drive patients to less-regulated sources, which increases the risk of contaminants and unpredictable amounts of active ingredients.

Patients need to be aware of the potential risk of cannabis products. It is important to know that state-regulated dispensaries usually test for product purity, although this varies between states. Unregulated cannabis may contain bacteria or fungus, heavy metals, pesticides or other harmful chemicals.

Lung damage from E-cigarettes and vaping has been linked to some products that contain cannabis. However, cannabis oil that is purchased in state-regulated dispensaries is widely thought to be safe if inhalation is the way it is taken. Vaping is preferred by patients using cannabis for for help with nausea and appetite.  Vaping cannabis oil is not recommended for patients with pulmonary issues or those undergoing stem cell transplant.  Vaping or smoking flower (dried herb) has risks related to fungus which should be avoided by most if not all cancer patients.

Because most medical oncologists do not feel they have adequate knowledge about cannabis to discuss its use with their patients, if you are interested in using cannabis for medical reasons, you may need to initiate a discussion with your doctor. If you are considering using cannabis to help manage treatment side effects and your oncologist does not feel comfortable discussing the subject with you, you can talk to others—members of your oncology team, registered dieticians, dispensary pharmacists—about the health and safety concerns associated with certain cannabis products.

It is important to tell your doctor if you are using cannabis so that they have full knowledge of the medically active drugs you are taking.


Among breast cancer patients, there is a strong interest in medical marijuana: almost half of the participants reported using it. Many believe that cannabis may have anticancer benefits (despite a lack of research data supporting this idea) and few talked to their healthcare providers about this. Participants reported using a range of cannabis products, which may vary in quality and purity. Most felt that cannabis products were safe. Most were also unaware of the risk of possible contaminants, potential interactions with other drugs or the possibility for products to be mislabeled.


Weiss MC, Hibbs JE, Buckley ME et al. A Coala-T-Cannabis Survey Study of breast cancer patients' use of cannabis before, during, and after treatment. Cancer. 2022. 128(1):160-168. Published online October 12, 2021.

Disclosure: FORCE receives funding from industry sponsors, including companies that manufacture cancer drugs, tests and devices. All XRAYS articles are written independently of any sponsor and are reviewed by members of our Scientific Advisory Board prior to publication to assure scientific integrity.

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posted 1/25/22

This article is relevant for:

People interested in using cannabis to relieve treatment side effects.

This article is also relevant for:

people with breast cancer

men with breast cancer

people with metastatic or advanced cancer

people newly diagnosed with cancer

Be part of XRAY:

Questions To Ask Your Doctor
Questions To Ask Your Doctor

  • Do you feel comfortable talking about using cannabis to help relieve treatment side effects?
  • Could cannabis reduce my treatment side effects and symptoms?
  • What are the risks or benefits of using cannabis?
  • What sources of cannabis do you recommend and why?
  • If you do not feel comfortable talking about using cannabis, can you recommend someone that I can talk to?

Open Clinical Trials
Open Clinical Trials

The following studies are looking at management of side effects: 

Multiple cancers

Breast cancer

Colorectal cancer

Endometrial cancer

Ovarian cancer

  • NCT04533763: Living WELL: A Web-Based Program for Ovarian Cancer Survivors. This studies a group-based and web-delivered tool for ovarian cancer survivors in increasing quality of life and decreasing stress, depressive mood, anxiety, and fatigue across a 12-month period.
  • NCT05047926: Prehabilitation for Advanced Ovarian Cancer Patients. Prehabilitation may improve peri-operative outcomes in patients undergoing cancer surgery. This study will look at structured activity for women undergoing chemotherapy to improve their physical state prior to surgical intervention and thus improve outcomes.


Updated: 02/15/2023

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