Herb library · Herb · Linum usitatissimum
Flaxseed
The seed of the flax plant (the source of linen), eaten ground or pressed for its oil, which is rich in the omega-3 fat ALA. Research is of varying quality: one trial suggests flaxseed mucilage might help with weight, while lignan extracts and the oil don't seem to.
Traditional use
First cultivated near the Middle East, flax was used for linen cloth in ancient Egypt, stews in Ethiopia and laxatives in ancient Greece; European settlers in North America made poultices for cuts and burns from the seed and paint from its oil. Today flaxseed and flaxseed oil supplements are promoted for the heart, brain and immune system.
What studies show
- Limited
Weight: one clinical trial suggests flaxseed mucilage powder mixed with water might help adults with overweight or obesity lose weight; flaxseed lignan extract and flaxseed oil don't seem to help.
- Limited
Gestational diabetes: some research suggests flaxseed oil supplements with ALA might improve fasting measures and insulin resistance in pregnant people with gestational diabetes.
- Insufficient
Type 2 diabetes and diabetic foot ulcers: more research is needed on whether lignan extract improves blood sugar control, and it is unclear whether flaxseed oil helps other people with diabetes.
Be careful of
Cautions
- NoteDon't eat raw or unripe flaxseeds; they may contain potentially toxic compounds.
- AmountLimited amounts, and flaxseed oil supplements, may be safe short term (up to 6 months). Higher doses can cause bloating, fullness and diarrhea.
- InteractionThere are theoretical reasons to expect interactions with blood thinners (anticoagulant and antiplatelet drugs).
- PregnancySome studies suggest flaxseed is possibly unsafe during pregnancy, though the evidence is not conclusive; little is known about flaxseed or its oil while breastfeeding, or the oil in pregnancy.
- Ask a clinicianTalk with a clinician or pharmacist before using this if you take prescription medicines, are pregnant or breastfeeding, or are giving it to a child.
From the old books
What herbals and dispensaries of the past printed. History, in their words.
“Flaxseed poultice causes the skin to be blanched, sodden, and wrinkled. Flaxseed poultice is frequently employed in acute pulmonic disorders.”
“The seeds finely ground, furnish a dark, ash-colored powder, flaxseed meal, which forms with hot water a tenacious substance, used for luting in chemical operations.”
In scripture
Where the Bible names this plant, and which plant scholars think is meant.
The flax and the barley were struck, for the barley had ripened and the flax was blooming.
Flax, the plant whose seed is on this page (Linum usitatissimum; Tristram, 1898, writes Linum sativum). These verses are about it as the source of linen, not of seed. H. B. Tristram, The Natural History of the Bible (1898), p. 445 (opens in a new tab)
But she had brought them up to the roof, and hidden them under the stalks of flax which she had laid in order on the roof.
Flax, the same plant as this page's seed, drying on a roof for its fiber (Tristram, 1898). H. B. Tristram, The Natural History of the Bible (1898), p. 445 (opens in a new tab)
Sources
- Flaxseed and Flaxseed Oil: Usefulness and Safety (opens in a new tab) · NCCIH · read September 25, 2026
Reviewed September 25, 2026.