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SupplementScience

Flaxseed Oil Side Effects & Safety

Reviewed by·PharmD, BCPS

This content is for informational purposes only and does not constitute medical advice. Consult your healthcare provider before starting any supplement. Full disclaimer

Safety Profile

Overall safety rating: Generally Safe

Potential Side Effects

  • Mild GI discomfort (bloating, loose stools) — most common at higher doses; usually resolves within a few days
  • Allergic reactions — rare but possible in individuals with flaxseed or linseed allergy
  • Increased bleeding tendency at very high doses — due to omega-3 antiplatelet effects
  • Estrogenic effects from lignans — theoretical concern in hormone-sensitive conditions, though clinical evidence suggests protective rather than stimulatory effects
  • Rapid oxidation if improperly stored — rancid flaxseed oil may cause nausea and has reduced nutritional value

Drug & Supplement Interactions

  • Anticoagulants and antiplatelets (warfarin, aspirin, clopidogrel) — ALA omega-3s have mild antiplatelet activity; may increase bleeding risk at high doses
  • Blood pressure medications — flaxseed oil may modestly lower blood pressure; monitor for additive hypotension
  • Blood sugar-lowering medications — some evidence flaxseed may affect glycemic control; monitor blood glucose
  • Hormone therapies and oral contraceptives — lignans have weak phytoestrogenic activity; theoretical interaction with estrogen-modulating drugs

Maximum Dose

Do not exceed: 4 tablespoons/day (60 mL); higher doses offer minimal additional benefit and may cause GI discomfort

Full Flaxseed Oil Guide

References

  1. Pan A, Yu D, Demark-Wahnefried W, Franco OH, Lin X (2009). Meta-analysis of the effects of flaxseed interventions on blood lipids. The American Journal of Clinical Nutrition. DOI PubMed
  2. Khalesi S, Irwin C, Schubert M (2015). Flaxseed consumption may reduce blood pressure: a systematic review and meta-analysis of controlled trials. The Journal of Nutrition. DOI PubMed
  3. Neukam K, De Spirt S, Stahl W, Bejot M, Maurette JM, Tronnier H, Heinrich U (2011). Supplementation of flaxseed oil diminishes skin sensitivity and improves skin barrier function and condition. Skin Pharmacology and Physiology. DOI PubMed
  4. Zhao G, Etherton TD, Martin KR, West SG, Gillies PJ, Kris-Etherton PM (2004). Dietary alpha-linolenic acid reduces inflammatory and lipid cardiovascular risk factors in hypercholesterolemic men and women. The Journal of Nutrition. DOI PubMed
  5. Burdge GC, Calder PC (2005). Conversion of alpha-linolenic acid to longer-chain polyunsaturated fatty acids in human adults. Reproduction, Nutrition, Development. DOI PubMed
  6. Rodriguez-Leyva D, Dupasquier CM, McCullough R, Pierce GN (2010). The cardiovascular effects of flaxseed and its omega-3 fatty acid, alpha-linolenic acid. Canadian Journal of Cardiology. DOI PubMed