Common Names

  • Flax
  • linseed
  • lint bells
  • linum

For Patients & Caregivers

How It Works

Flaxseed appears to be effective in reducing menopausal symptoms, but evidence of its ability to reduce cholesterol levels is mixed.

Flaxseed is a very concentrated source of phytoestrogenic compounds called lignans, which have hormone-like effects on the body (soybeans are another source of phytoestrogens). These lignans are likely the reason why flaxseed can affect menstrual cycle length and menopausal symptoms. It contains alpha-linolenic acid (ALA), a building block of omega-3 fatty acids. ALA has been shown to have numerous effects on the body including protecting the kidneys from damage. Results from clinical studies are mixed on flaxseed’s ability to reduce cholesterol.

Flaxseed has also been shown to affect intracellular signals within the body that may play a role in breast and prostate cancer growth. Because flaxseed has phytoestrogenic effects, patients with estrogen receptor positive (ER+) breast cancer should use flaxseed with caution.

Purported Uses

  • Cancer prevention
    Studies of postmenopausal women showed that flaxseed supplementation improved the ratio of hormones that are thought to help prevent breast cancer. Studies in animals have shown promising results, but human data are lacking.
  • High cholesterol
    Study results are mixed.
  • Menopausal symptoms
    A study showed flaxseed to be as effective as hormone replacement therapy in the management of menopausal symptoms.
  • Mucositis
    One study indicated that flaxseed was not effective for mucositis.
  • Periodontal disease
    Flaxseed was shown ineffective against periodontal disease in a study.

Do Not Take If

  • You are undergoing radiological procedures as linseed may interfere with the reading of certain tests.

Side Effects

  • Allergic reactions
  • Increase of the luteal phase of the menstrual cycle
  • Increased bowel movement
  • Constipation
  • Flatulence
    Case Reports:
  • Anaphylaxis has been reported following intake of flaxseeds.
  • Dietary flaxseed was shown to worsen dextran sodium sulfate-induced colonic injury and inflammation in mice.
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For Healthcare Professionals

Brand Name

Salinum ®, Brevail®

Scientific Name

Linum usitatissimum

Clinical Summary

Flaxseed has been used in traditional medicine to treat coughs, colds, constipation, urinary tract infections, as a topical demulcent and as an emollient (1). It is rich in omega-3 fatty acids and phytoestrogenic lignans. Flaxseed was shown to have chemoprotective effects in postmenopausal women (2), conferred renoprotection in patients with lupus nephritis (3), and improved mild menopausal symptoms (11). Supplementation with a major lignan derived from flaxseed improved glycemic control in Type-2 diabetic patients (13), and a meta analysis showed significant reductions in blood pressure following supplementation with flaxseed products (34). Although flaxseed-derived lignan reduces blood glucose levels in hypercholesterolemic individuals (14), data on the cholesterol-lowering effects of flaxseed are mixed (11) (15) (26). Flaxseed supplementation may benefit women with polycystic ovarian syndrome by reducing androgen levels (23); a moderate reduction of estrogens and androgens was also seen in postmenopausal women (24). However, lignan supplementation was ineffective in reducing hot flashes in postmenopausal women with or without breast cancer (28)

Flaxseed has been investigated for its anticancer potential. It was shown to inhibit the growth and metastasis of human breast cancer (6) (29), prostate cancer (7) and melanoma (8) in vitro and in mice. It also reduced radiation therapy-induced lung damage and improved survival (27). In other studies, flaxseed was shown to lower tumor biomarkers in men with prostate cancer (9) (25) and in patients with breast cancer (10), but a flaxseed extract was ineffective in preventing oral infection following radiation treatment for head and neck cancer (12).

Flaxseed ingestion can increase urinary lignan excretion (4) and the length of the luteal phase of the menstrual cycle (5).

Purported Uses

  • Cancer prevention
  • Constipation
  • High cholesterol
  • Menopausal symptoms
  • Mucositis
  • Periodontal disease
  • Premenstrual syndrome
  • Radiation therapy side effects

Mechanism of Action

Flaxseed is the most concentrated food source of the plant lignan, secoisolariciresinol, a precursor for enterolactone. It is thought that phytoestrogenic lignans contribute to the plant’s hormonal effects (4). Flaxseed has been shown to affect the length of the menstrual cycle in premenopausal women (5). It may also alter estrogen metabolism, increasing the ratio of 2-hydroxyestrogen to 16 alpha-hydroxyestrone in a dose dependent fashion (2). Flaxseed’s renoprotective effects are thought to be via high concentration of alpha-linolenic acid, an omega-3 fatty acid precursor (3) or through inhibition of angiogenesis, tyrosine protein kinases and cytokine-induced activation of transcription factors (16). The laxative effects of flaxseed are likely due to its fiber content (22).

In addition, flaxseed’s inhibition of growth of human breast cancer, and metastasis in mice is due in part to the down-regulation of insulin-like growth factor I and expression of epidermal growth factor receptor (6). Flaxseed was also shown to induce apoptosis by significantly upregulating p53 mRNA in breast cancer cell lines (29). In another study, flaxseed oil enhanced the effects of trastuzumab in reducing HER2 signaling via the Akt and mitogen-activated protein kinase (MAPK) pathways, resulting in reduction in cell proliferation and an increase in apoptosis (33).

The antiproliferative activity of flaxseed against prostate cancer in mice is attributed to its inhibition of cellular proliferation (7). The hormonal effects of flaxseed may also play a role in its ability to modulate prostate cancer biology and associated biomarkers (9), and lower serum lipid levels (10).


Because flaxseed has phytoestrogenic effects, patients with estrogen receptor positive (ER+) breast cancer should use flaxseed with caution.

Adverse Reactions

Common: Increased bowel movements (16), constipation and flatulence (9)
Case Reports:
Anaphylaxis has been reported following ingestion of flaxseeds. (17) (30)
A case of false polyposis coli on double contrast barium enema (18), and an increase in the luteal phase of the menstrual cycle (5) were observed after flaxseed supplementation.
Dietary flaxseed was shown to exacerbate dextran sodium sulfate-induced colonic injury and inflammation in mice (31).

Dosage (OneMSK Only)


  1. DerMarderosian A. The Review of Natural Products. St. Louis: Facts and Comparisons, 1999.

  2. Haggans CJ, Hutchins AM, Olson BA, Thomas W, Martini MC, Slavin JL. Effect of flaxseed consumption on urinary estrogen metabolites in postmenopausal women. Nutrition & Cancer. 1999;33:188-95.

  3. Clark WF, Kortas C, Heidenheim AP, Garland J, Spanner E, Parbtani A. Flaxseed in lupus nephritis: a two-year nonplacebo-controlled crossover study. Journal of the American College of Nutrition. 2001;20:Suppl-8.

  4. Hutchins AM, Martini MC, Olson BA, Thomas W, Slavin JL. Flaxseed influences urinary lignan excretion in a dose-dependent manner in postmenopausal women. Cancer Epidemiology, Biomarkers & Prevention. 2000;9:1113-8.

  5. Phipps WR, Martini MC, Lampe JW, Slavin JL, Kurzer MS. Effect of flax seed ingestion on the menstrual cycle. J Clin Endocrinol.Metab 1993;77:1215-9.

  6. Lin X, Gingrich JR, Bao W, Li J, Haroon ZA, Demark-Wahnefried W. Effect of flaxseed supplementation on prostatic carcinoma in transgenic mice. Urology 2002;60:919-24.

  7. Yan L, Yee JA, Li D, McGuire MH, Thompson LU. Dietary flaxseed supplementation and experimental metastasis of melanoma cells in mice. Cancer Letters. 1998;124:181-6.

  8. Thompson LU, Chen JM, Li T, Strasser-Weippl K, Goss, PE. Dietary flaxseed alters tumor biological markers in postmenopausal breast cancer. Clin Cancer Res. 2005;11(10):3828-3835.

  9. Lemay A, Dodin S, Kadri N, Jacques H, Forest JC. Flaxseed dietary supplement versus hormone replacement therapy in hypercholesterolemic menopausal women. Obstetrics & Gynecology. 2002;100:495-504.

  10. Johansson G, Andersson G, Attstom R, Edwardsson S. Oral mucous membrane flora in patients using saliva substitutes. Gerodontology. 2000;17:87-90.

  11. Cunnane SC, Hamadeh MJ, Liede AC, Thompson LU, Wolever TM, Jenkins DJ. Nutritional attributes of traditional flaxseed in healthy young adults. Am J Clin Nutr 1995;61:62-8.

  12. Leon F, Rodriguez M, Cuevas M. Anaphylaxis to Linum. Allergologia et Immunopathologia. 2003;31:47-9.

  13. Petty DR,.Mannion RA. A case of multiple linseeds mimicking polyposis coli on double contrast barium enema. Clinical Radiology. 2003;58:87-8.

  14. Ranich T, Bhathena SJ, Velasquez MT. Protective effects of dietary phytoestrogens in chronic renal disease. Journal of Renal Nutrition. 2001;11:183-93.

  15. Nesbitt PD, Lam Y, Thompson LU. Human metabolism of mammalian lignan precursors in raw and processed flaxseed. Am J Clin Nutr. 1999;69:549-55.

  16. Dahl WJ, Lockert EA, Cammer AL, et al. Effects of flax fiber on laxation and glycemic response in healthy volunteers. J Med Food. 2005 Winter;8(4):508-11.

  17. Nowak DA, Snyder DC, Brown AJ, Demark-Wahnefried W. The Effect of Flaxseed Supplementation on Hormonal Levels Associated with Polycystic Ovarian Syndrome: A Case Study. Curr Top Nutraceutical Res. 2007;5(4):177-181.

  18. Sturgeon SR, Heersink JL, Volpe SL, et al. Effect of dietary flaxseed on serum levels of estrogens and androgens in postmenopausal women. Nutr Cancer. 2008;60(5):612-8.

  19. Demark-Wahnefried W, Polascik TJ, George SL, et al. Flaxseed supplementation (not dietary fat restriction) reduces prostate cancer proliferation rates in men presurgery. Cancer Epidemiol Biomarkers Prev. 2008 Dec;17(12):3577-87.

  20. Alvarez-Perea A, Alzate -Pérez D, Doleo Maldonado A, Baeza ML. Anaphylaxis caused by flaxseed. J Investig Allergol Clin Immunol. 2013;23(6):446-7.

  21. Zarepoor L, Lu JT, Zhang C, et al. Dietary flaxseed intake exacerbates acute colonic mucosal injury and inflammation induced by dextran sodium sulfate. Am J Physiol Gastrointest Liver Physiol. 2014 Jun 15;306(12):G1042-55.

  22. Herchi W, Arráez-Román D, Trabelsi H, et al. Phenolic compounds in flaxseed: a review of their properties and analytical methods. An overview of the last decade. J Oleo Sci. 2014;63(1):7-14.

  23. Ursoniu S, Sahebkar A, Andrica F, Serban C, Banach M; Lipid and Blood Pressure Meta-analysis Collaboration (LBPMC) Group. Effects of flaxseed supplements on blood pressure: A systematic review and meta-analysis of controlled clinical trial. Clin Nutr. 2016 Jun;35(3):615-25.

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