Common Names

  • Flax
  • Linseed
  • Lint bells
  • Linum

For Patients & Caregivers

How It Works

Flaxseed may help improve mild menopausal symptoms and reduce blood pressure, but evidence of its ability to improve cholesterol levels is mixed.

Flaxseed is a concentrated source of phytoestrogenic compounds called lignans, which have hormone-like effects on the body. 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. Other studies suggest it may reduce blood pressure and help with some aspects of diabetes or related conditions, especially along with other lifestyle modifications. 

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 consult their physicians before using flaxseed.

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.
  • Diabetes and associated conditions
    Some studies suggest supplementation with flaxseed may help some aspects of diabetes or related conditions, especially along with other lifestyle modifications. 
  • 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: Flax or linseed may interfere with the reading of certain tests.
Side Effects
  • Allergic reactions
  • Longer luteal phase of the menstrual cycle
  • Increased bowel movement
  • Constipation
  • Flatulence

Case Reports

  • Anaphylaxis following intake of flaxseeds
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For Healthcare Professionals

Brand Name
Salinum®, Brevail®
Scientific Name
Linum usitatissimum
Clinical Summary

Flaxseed, rich in omega-3 fatty acids and phytoestrogenic lignans, has been used in traditional medicine to treat coughs, colds, constipation, urinary tract infections, and as a topical demulcent and emollient. In clinical studies, flaxseed improved mild menopausal symptoms (11); and exerted chemoprotective effects (2) along with affecting moderate reductions in estrogens and androgens (24) in postmenopausal women. It may also benefit women with polycystic ovarian syndrome by reducing androgen levels (23); and flaxseed powder combined with Vitex agnus may help to reduce cyclical mastalgia (39).

In other studies, supplementation with a major lignan derived from flaxseed improved glycemic control in Type-2 diabetic patients (13). However, it was ineffective in reducing hot flashes in postmenopausal women with or without breast cancer (28). Flaxseed products have also been shown to reduce blood pressure (1) (34) (40) (41). In pre-diabetic patients, daily intake of flaxseed powder lowered blood pressure but did not improve insulin resistance or glycemic indices (35). Supplementation along with lifestyle modification was more effective than lifestyle modification alone to manage metabolic syndrome (36) and non-alcoholic fatty liver disease (37). Flaxseed was also found more effective than psyllium for improving symptoms of constipation, as well as glycemic and lipid levels (42). In patients with ulcerative colitis, both flaxseed and flaxseed oil were reported to reduce inflammatory markers, disease severity, and blood pressure (44). Daily flaxseed oil consumption also significantly reduced inflammatory markers related to cardiovascular disease (38), and may help reduce bone resorption (43) in hemodialysis patients. Furthermore, flaxseed conferred renoprotection in patients with lupus nephritis (3), but additional studies are needed.

Although flaxseed-derived lignan reduced blood glucose levels in hypercholesterolemic individuals (14), data on its cholesterol-lowering effects are mixed (11) (15) (26).

Flaxseed has also been investigated for its anticancer potential. Preclinical studies suggest it may inhibit growth and metastasis of human breast (6) (29), prostate (7) cancers and melanoma (8); and may reduce radiation therapy-induced lung damage and improve survival (27). Flaxseed was reported to lower tumor biomarkers in patients with prostate (9) (25) and breast cancer (10). But a flaxseed extract was ineffective in preventing oral infection following radiation treatment in head and neck cancer patients (12); and supplementation with secoisolariciresinol diglucoside, a lignan, was not superior to placebo in reducing proliferation in benign breast tissue of premenopausal women at increased risk of breast cancer (45).

Flaxseed ingestion can increase urinary lignan excretion (4) and the length of the luteal phase of the menstrual cycle (5). Because flaxseed has phytoestrogenic effects, patients with estrogen receptor positive (ER+) breast cancer should consult their physicians before using it.

Purported Uses
  • Cancer prevention
  • Diabetes
  • High cholesterol
  • Menopausal symptoms
  • Mucositis
  • Periodontal disease
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). The renoprotective effects of flaxseed are thought to be due to 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).

Animal studies suggest inhibition of growth and metastasis of established human breast cancer with flaxseed is due in part to downregulation of insulin-like growth factor I and expression of the epidermal growth factor receptor (6). Flaxseed also induced apoptosis by significantly upregulating p53 mRNA in breast cancer cell lines (29). In another study, flaxseed oil enhanced effects of trastuzumab in reducing HER2 signaling via Akt and mitogen-activated protein kinase (MAPK) pathways, resulting in reduced cell proliferation and increased apoptosis (33). Inhibition of cell proliferation with flaxseed was also reported in models of prostate cancer (7).

In human studies, dietary flaxseed reduced central aortic blood pressure through changes in plasma oxylipins (40) (41). Other studies suggest hormonal effects may play a role in the ability of flaxseed to modulate prostate cancer biology and associated biomarkers (9), and lower serum lipid levels in postmenopausal breast cancer (10).

Adverse Reactions

Common: Increased bowel movements (16), constipation, and flatulence (9)

Case Reports
Anaphylaxis: Following ingestion of flaxseeds (17) (30).
False polyposis coli: On double contrast barium enema after flaxseed supplementation (18).
Increase in the luteal phase of the menstrual cycle: After flaxseed supplementation (5).

Dosage (OneMSK Only)
  1. Di Y, Jones J, Mansell K, et al. Influence of flaxseed lignan supplementation to older adults on biochemical and functional outcome measures of inflammation. J Am Coll Nutr. Nov-Dec 2017;36(8):646-653.
  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. Chen J, Stavro PM, Thompson LU. Dietary flaxseed inhibits human breast cancer growth and metastasis and downregulates expression of insulin-like growth factor and epidermal growth factor receptor. Nutrition & Cancer. 2002;43:187-92.
  7. 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.
  8. 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.
  9. Demark-Wahnefried W, Price DT, Polascik TJ, Robertson CN, Anderson EE, Paulson DF et al. Pilot study of dietary fat restriction and flaxseed supplementation in men with prostate cancer before surgery: exploring the effects on hormonal levels, prostate-specific antigen, and histopathologic features. Urology 2001;58:47-52.
  10. 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.
  11. 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.
  12. Johansson G, Andersson G, Attstom R, Edwardsson S. Oral mucous membrane flora in patients using saliva substitutes. Gerodontology. 2000;17:87-90.
  13. Pan A, Sun J, Chen Y, et al. Effects of a flaxseed-derived lignan supplement in type 2 diabetic patients: a randomized, double-blind, cross-over trial. PLoS ONE 2007;2(11):e1148.
  14. Zhang W, Wang X, Liu Y, et al. Dietary flaxseed lignan extract lowers plasma cholesterol and glucose concentrations in hypercholesterolaemic subjects. Br J Nutr. 2008 Jun;99(6):1301-9.
  15. Jenkins DJ, Kendall CW, Vidgen E, Agarwal S, Rao AV, Rosenberg RS et al. Health aspects of partially defatted flaxseed, including effects on serum lipids, oxidative measures, and ex vivo androgen and progestin activity: a controlled crossover trial. Am J Clin Nutr. 1999;69:395-402.
  16. 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.
  17. Leon F, Rodriguez M, Cuevas M. Anaphylaxis to Linum. Allergologia et Immunopathologia. 2003;31:47-9.
  18. Petty DR,.Mannion RA. A case of multiple linseeds mimicking polyposis coli on double contrast barium enema. Clinical Radiology. 2003;58:87-8.
  19. Ranich T, Bhathena SJ, Velasquez MT. Protective effects of dietary phytoestrogens in chronic renal disease. Journal of Renal Nutrition. 2001;11:183-93.
  20. 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.
  21. Brooks JD, Ward WE, Lewis JE, et al. Supplementation with flaxseed alters estrogen metabolism in postmenopausal women to a greater extent than does supplementation with an equal amount of soy. Am J Clin Nutr 2004 Feb;79(2):318-25.
  22. 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.
  23. 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.
  24. 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.
  25. 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.
  26. Fukumitsu S, Aida K, Shimizu H, Toyoda K. Flaxseed lignan lowers blood cholesterol and decreases liver disease risk factors in moderately hypercholesterolemic men. Nutr Res. 2010 Jul;30(7):441-6.
  27. Christofidou-Solomidou M, Tyagi S, Tan KS, et al. Dietary flaxseed administered post thoracic radiation treatment improves survival and mitigates radiation-induced pneumonopathy in mice. BMC Cancer. 2011 Jun 24;11:269.
  28. Pruthi S, Qin R, Terstreip SA et al. A phase III, randomized, placebo-controlled, double-blind trial of flaxseed for the treatment of hot flashes: North Central Cancer Treatment Group N08C7. Menopause. 2012 Jan;19(1):48-53.
  29. Lee J, Cho K. Flaxseed sprouts induce apoptosis and inhibit growth in MCF-7 and MDA-MB-231 human breast cancer cells. In Vitro Cell Dev Biol Anim. 2012 Apr;48(4):244-50.
  30. 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.
  31. 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.
  32. 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.
  33. Mason JK, Fu M, Chen J, Thompson LU. Flaxseed oil enhances the effectiveness of trastuzumab in reducing the growth of HER2-overexpressing human breast tumors (BT-474). J Nutr Biochem. 2015 Jan;26(1):16-23.
  34. 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.
  35. Javidi A, Mozaffari-Khosravi H, Nadjarzadeh A, et al. The effect of flaxseed powder on insulin resistance indices and blood pressure in prediabetic individuals: A randomized controlled clinical trial. J Res Med Sci. 2016;21:70.
  36. Yari Z, Rahimlou M, Poustchi H, et al. Flaxseed Supplementation in Metabolic Syndrome Management: A Pilot Randomized, Open-labeled, Controlled Study. Phytother Res. Aug 2016;30(8):1339-1344.
  37. Yari Z, Rahimlou M, Eslamparast T, et al. Flaxseed supplementation in non-alcoholic fatty liver disease: a pilot randomized, open labeled, controlled study. Int J Food Sci Nutr. Jun 2016;67(4):461-469.
  38. Mirfatahi M, Tabibi H, Nasrollahi A, et al. Effect of flaxseed oil on serum systemic and vascular inflammation markers and oxidative stress in hemodialysis patients: a randomized controlled trial. Int Urol Nephrol. Aug 2016;48(8):1335-1341.
  39. Mirghafourvand M, Mohammad-Alizadeh-Charandabi S, Ahmadpour P, et al. Effects of Vitex agnus and Flaxseed on cyclic mastalgia: A randomized controlled trial. Complement Ther Med. Feb 2016;24:90-95.
  40. Caligiuri SP, Aukema HM, Ravandi A, et al. Flaxseed consumption reduces blood pressure in patients with hypertension by altering circulating oxylipins via an alpha-linolenic acid-induced inhibition of soluble epoxide hydrolase. Hypertension. Jul 2014;64(1):53-59.
  41. Caligiuri SP, Rodriguez-Leyva D, Aukema HM, et al. Dietary Flaxseed Reduces Central Aortic Blood Pressure Without Cardiac Involvement but Through Changes in Plasma Oxylipins. Hypertension. Oct 2016;68(4):1031-1038.
  42. Soltanian N, Janghorbani M. Effect of flaxseed or psyllium vs. placebo on management of constipation, weight, glycemia, and lipids: A randomized trial in constipated patients with type 2 diabetes. Clin Nutr ESPEN. 2019 Feb;29:41-48.
  43. Mirfatahi M, Imani H, Tabibi H, Nasrollahi A, Hedayati M. Effects of Flaxseed Oil on Serum Bone Turnover Markers in Hemodialysis Patients: a Randomized Controlled Trial. Iran J Kidney Dis. 2018 Jul;12(4):215-222.
  44. Morshedzadeh N, Shahrokh S, Aghdaei HA, et al. Effects of flaxseed and flaxseed oil supplement on serum levels of inflammatory markers, metabolic parameters and severity of disease in patients with ulcerative colitis. Complement Ther Med. 2019 Oct;46:36-43.
  45. Fabian CJ, Khan SA, Garber JE, et al. Randomized Phase IIB Trial of the Lignan Secoisolariciresinol Diglucoside in Pre-menopausal Women at Increased Risk for Development of Breast Cancer. Cancer Prev Res (Phila). 2020 Apr 20. pii: canprevres.0050.2020.
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