Purported Benefits, Side Effects & More


Purported Benefits, Side Effects & More

Common Names

  • Flax
  • Linseed
  • Lint bells
  • Linum

For Patients & Caregivers

Tell your healthcare providers about any dietary supplements you’re taking, such as herbs, vitamins, minerals, and natural or home remedies. This will help them manage your care and keep you safe.

What is it?

Flaxseed comes from the flax plant. It has omega-3 fatty acids and fiber. Flaxseed is also a source of plant-based estrogens that have hormone-like effects in the body. They may help mild menopausal symptoms like hot flashes.

Flaxseed is in many different foods including crackers, waffles, and oatmeal. You can also get flaxseed whole or grounded to use in foods and drinks.

What are the potential uses and benefits?

Flaxseed is used to:

  • Prevent breast, prostate, and colon cancer
  • Control blood sugar level in patients with type-2 diabetes
  • Lower high cholesterol
  • Manage symptoms of menopause (permanent end of menstrual cycles) such as hot flashes and night sweats
  • Treat constipation (difficult or infrequent bowel movements)

Flaxseed also has other uses that haven’t been studied by doctors to see if they work.

It’s generally safe to use flaxseed in food and drinks but talk with your healthcare providers before taking flaxseed supplements. Herbal supplements are stronger than the herbs you would use in cooking.

Supplements can also interact with some medications and affect how they work. For more information, read the “What else do I need to know?” section below.

What are the side effects?

Side effects of using flaxseed can include:

  • Allergic reactions
  • Increased bowel movements (poop)
  • Constipation (having fewer bowel movements than usual)
  • Having gas
What else do I need to know?
  • Talk to your doctor if you’re going to have radiology procedure such as double contrast barium enema. Flaxseed may affect the results of your test.
  • Talk with your doctor or Registered Dietitian if you have questions about adding flaxseed to your food or taking it as a supplement.

For Healthcare Professionals

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

Flaxseed, rich in omega-3 fatty acids and phytoestrogenic lignans, is used in traditional medicine to treat coughs, colds, constipation, urinary tract infections, and as a topical demulcent and an 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 reduce cyclical mastalgia (39). Supplementation with a major lignan derived from flaxseed improved glycemic control in Type-2 diabetic patients (13). But it was ineffective in reducing hot flashes in postmenopausal women with or without breast cancer (28).
In other studies, flaxseed products were found to reduce blood pressure (1) (34) (40) (41) (35) (53) but did not improve insulin resistance or glycemic indices in pre-diabetic patients (35) although conflicting data suggest otherwise (49) (54). Supplementation along with lifestyle modification was more effective than lifestyle modification alone to manage metabolic syndrome (36) and non-alcoholic fatty liver disease (37) (46). Systematic reviews determined that flaxseed may have a role in decreasing appetite and hunger (55) and in preventing cardiovascular events by inhibiting platelet aggregation (56). It was also found more effective than lactulose (47) and psyllium for improving symptoms of constipation (42). In patients with ulcerative colitis, both flaxseed and flaxseed oil may affect reductions in systemic inflammation (50) as well as disease severity (44). In addition, daily flaxseed oil consumption significantly decreased inflammatory markers related to cardiovascular disease (38), and may help reduce bone resorption (43) in hemodialysis patients. Flaxseed was also shown to confer renoprotection in patients with lupus nephritis (3); and may benefit patients with rheumatoid arthritis (51).

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

Preclinical studies suggest that flaxseed may inhibit growth and metastasis of human breast (6) (29), prostate (7) cancers and melanoma (8); and reduce radiation therapy-induced lung damage and improve survival (27). It was also shown to lower tumor biomarkers in patients with prostate (9) (25) and breast cancer (10); and may confer protection against radiation-induced adverse effects in lung cancer patients although such effects could not be accurately determined due to poor tolerability of flaxseed (52). In other studies, 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 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 and Benefits
  • Cancer prevention
  • Diabetes
  • High cholesterol
  • Menopausal symptoms
  • Constipation
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).
Gynecomastia: In a 70-year-old male patient after taking flaxseed oil for three months to address hyperlipidaemia (48).
Cutaneous pseudolymphomatous drug eruption: In a 51-year-old woman after using flaxseed oil. The rash resolved after discontinuing oil use (57).

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.
  46. Rezaei S, Sasani MR, Akhlaghi M, Kohanmoo A. Flaxseed oil in the context of a weight loss programme ameliorates fatty liver grade in patients with non-alcoholic fatty liver disease: a randomised double-blind controlled trial. Br J Nutr. 2020 May 14;123(9):994-1002.
  47. Sun J, Bai H, Ma J, et al. Effects of flaxseed supplementation on functional constipation and quality of life in a Chinese population: A randomized trial. Asia Pac J Clin Nutr. 2020;29(1):61-67.
  48. Takenaka T, Nagano M, Yamashita K, Kikuchi K. Flaxseed oil stimulates gynecomastia. BMJ Case Rep. 2020 Dec 10;13(12):e237948.
  49. Mahdavi A, Bagherniya M, Mirenayat MS, Atkin SL, Sahebkar A. Medicinal Plants and Phytochemicals Regulating Insulin Resistance and Glucose Homeostasis in Type 2 Diabetic Patients: A Clinical Review. Adv Exp Med Biol. 2021;1308:161-183.
  50. Morshedzadeh N, Shahrokh S, Chaleshi V, Karimi S, Mirmiran P, Zali MR. The effects of flaxseed supplementation on gene expression and inflammation in ulcerative colitis patients: An open-labelled randomised controlled trial. Int J Clin Pract. 2021 May;75(5):e14035.
  51. Ghaseminasab-Parizi M, Nazarinia MA, Akhlaghi M. The effect of flaxseed with or without anti-inflammatory diet in patients with rheumatoid arthritis, a randomized controlled trial. Eur J Nutr. 2022 Apr;61(3):1377-1389.
  52. Lim TL, Pietrofesa RA, Arguiri E, et al. Phase II Trial of Flaxseed to Prevent Acute Complications After Chemoradiation for Lung Cancer. J Altern Complement Med. 2021 Oct;27(10):824-831.
  53. Mahmudiono T, Jasim SA, Karim YS, et al. The effect of flaxseed oil consumtion on blood pressure among patients with metabolic syndrome and related disorders: A systematic review and meta-analysis of randomized clinical trials. Phytother Res. 2022 Oct;36(10):3766-3773.
  54. Villarreal-Renteria AI, Herrera-Echauri DD, Rodríguez-Rocha NP, et al. Effect of flaxseed (Linum usitatissimum) supplementation on glycemic control and insulin resistance in prediabetes and type 2 diabetes: A systematic review and meta-analysis of randomized controlled trials. Complement Ther Med. 2022 Nov;70:102852.
  55. Zarei M, Adeli S, Hosseini S, Daneshzad E. The effect of flaxseed intake on appetite reduction: A systematic review of randomized clinical trials. Phytother Res. 2022 Oct;36(10):3792-3804.
  56. Nouruzi S, Vasheghani Farahani A, Rezaeizadeh H, et al. Platelet Aggregation Inhibition: An Evidence-Based Systematic Review on the Role of Herbs for Primary Prevention Based on Randomized Controlled Trials. Iran J Med Sci. 2022 Nov;47(6):505-516.
  57. Larson EL, Scheufele C, Rohr BR, Honda K, Cooper K. Cutaneous pseudolymphomatous drug eruption secondary to supplemental flaxseed oil. JAAD Case Rep. 2022 Jun 3;27:82-84.
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