This food and dietary supplement may reduce prostate cancer spread, improve survival in breast cancer, and lower the risk of several cancers.

Safety and precautions

Flaxseeds and flaxseed supplements are generally well tolerated and considered safe, but bloating and gastrointestinal effects may occur. Flaxseed oil should not be heated. High doses of flaxseed lignans such as high-lignan flax oil may cause side effects and interactions. 

Do not heat flaxseed oil, as the heat will damage the oil and form dangerous compounds.1Lemole G, Mehta P, McKee D. After Cancer Care: The Definitive Self-Care Guide to Getting and Staying Well for Patients with Cancer. New York, New York: Rodale, Inc. 2015. However, studies have shown that when whole or ground flaxseeds are heated at temperatures consistent with baking, lignans and alpha-linolenate (an omega-3 fatty acid) are not degraded.2Gerstenmeyer E, Reimer S, Berghofer E, Schwartz H, Sontag G. Effect of thermal heating on some lignans in flax seeds, sesame seeds and rye. Food Chemistry. 2013 Jun 1;138(2-3):1847-55; Cunnae SC, Hamadeh MJ et al. Nutritional attributes of traditional flaxseed in healthy young adults. American Journal of Clinical Nutrition. 1995 Jan;61(1):62-8.  

Because flaxseed does not contain all three essential omega-3 fatty acids, using flaxseed as your only source of omega-3s may lead to insufficient levels of DHA and EPA.

Side effects or adverse events

Bloating and gastrointestinal effects were cited as side effects and the cause of treatment discontinuation for 3 study participants in an uncontrolled trial.3Pruthi S, Thompson SL et al. Pilot evaluation of flaxseed for the management of hot flashes. Journal of the Society for Integrative Oncology. 2007 Summer;5(3):106-12. 

High doses of flaxseed lignans such as high-lignan flaxseed oil may lead to weight gain.4Stein N. The dangers of high lignan flax seed oil. Viewed May 17, 2019.

Interactions with other therapies

Interactions of high doses of flaxseed lignans such as high-lignan flaxseed oil:5Stein N. The dangers of high lignan flax seed oil. Viewed May 17, 2019.

  • An additive effect on blood thinners
  • Interactions with medications for managing blood sugar

In animals, a diet comprising 10% flaxseed and equivalent lignans did not interfere with but rather increased the effectiveness of tamoxifen (80 mg/day) while a diet of 4% flaxseed oil increased trastuzumab/Herceptin (2.5 mg/kg) effectiveness.6Mason JK, Thompson LU. Flaxseed and its lignan and oil components: can they play a role in reducing the risk of and improving the treatment of breast cancer? Applied Physiology, Nutrition, and Metabolism. 2014 Jun;39(6):663-78.

Keep reading about flaxseed


Maria Williams

Research and Communications Consultant
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Maria Williams is a research and communications consultant who brings over 15 years’ experience in research, consumer education, and science communication to CancerChoices. She has worked primarily in public health and environmental health.

Maria Williams Research and Communications Consultant

Nancy Hepp, MS

Lead Researcher
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Ms. Hepp is a researcher and communicator who has been writing and editing educational content on varied health topics for more than 20 years. She serves as lead researcher and writer for CancerChoices and also served as the first program manager. Her graduate work in research and cognitive psychology, her master’s degree in instructional design, and her certificate in web design have all guided her in writing and presenting information for a wide variety of audiences and uses. Nancy’s service as faculty development coordinator in the Department of Family Medicine at Wright State University also provided experience in medical research, plus insights into medical education and medical care from the professional’s perspective.

Nancy Hepp, MS Lead Researcher


Laura Pole, MSN, RN, OCNS

Senior Clinical Consultant
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Laura Pole is senior clinical consultant for CancerChoices. Laura is an oncology clinical nurse specialist who has been providing integrative oncology clinical care, navigation, consultation, and education services for over 40 years. She is the co-creator and co-coordinator of the Integrative Oncology Navigation Training at Smith Center for Healing and the Arts in Washington, DC. Laura also manages the “Media Watch Cancer News That You Can Use” listserv for Smith Center/Commonweal. In her role as a palliative care educator and consultant, Laura has served as statewide Respecting Choices Faculty for the Virginia POST (Physician Orders for Scope of Treatment) Collaborative as well as provided statewide professional education on palliative and end-of-life care for the Virginia Association for Hospices and Palliative Care.

For CancerChoices, Laura curates content and research, networks with clinical and organizational partners, brings awareness and education of integrative oncology at professional and patient conferences and programs, and translates research into information relevant to the patient experience as well as clinical practice.

Laura sees her work with CancerChoices as a perfect alignment of all her passions, knowledge and skills in integrative oncology care. She is honored to serve you.

Laura Pole, MSN, RN, OCNS Senior Clinical Consultant

Last update: December 11, 2023

Last full literature review: September 2021

CancerChoices provides information about integrative in cancer care, a patient-centered approach combining the best of conventional care, self care and evidence-informed complementary care in an integrated plan cancer care. We review complementaryin cancer care, complementary care involves the use of therapies intended to enhance or add to standard conventional treatments; examples include supplements, mind-body approaches such as yoga or psychosocial therapy, and acupuncture therapies and self-care lifestyle actions and behaviors that may impact cancer outcomes; examples include eating health-promoting foods, limiting alcohol, increasing physical activity, and managing stress practices to help patients and professionals explore and integrate the best combination of conventionalthe cancer care offered by conventionally trained physicians and most hospitals; examples are chemotherapy, surgery, and radiotherapy and complementary therapies and practices for each person.

Our staff have no financial conflicts of interest to declare. We receive no funds from any manufacturers or retailers gaining financial profit by promoting or discouraging therapies mentioned on this site.

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