Flaxseed
Summary
Ground flaxseed has some of the better trial evidence among food supplements. A meta-analysis of 33 trials (2,427 people) found about 3 mmHg lower systolic blood pressure, with larger drops at 30 g/day or more, and 62 RCTs (3,772 people) found small LDL and triglyceride reductions (grade B). A 188-woman trial found flax lignans did not ease hot flashes.
Key facts
- Seed of Linum usitatissimum; a food source of ALA omega-3, lignans and fiber, sold whole, milled, as oil or as lignan extract[1]
- Blood pressure: modest reduction (B); LDL and triglycerides: small reduction (B); fasting glucose and insulin: small reduction in pooled trials (C); hot flashes: no effect (B)[2][5][6][7]
- Larger blood-pressure effects at 30 g/day or more of flaxseed for over 20 weeks; the landmark trial used 30 g/day milled flaxseed for 6 months[2][4]
- None set; flaxseed is a food[1]
- Theoretical interaction with anticoagulant and antiplatelet drugs; none confirmed in trials[1]
- 5 graded human outcomes on this page
- October 10, 2026
How it works
ProposedFlaxseed supplies alpha-linolenic acid, lignans that gut bacteria convert to enterolignans, and fiber. In a 6-month trial, blood ALA and enterolignans rose 2- to 50-fold and ALA levels tracked with lower blood pressure, but which component drives the effect is not settled.[4]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Cholesterol | Grade B | Improved | Meta-analysis of 62 trials · n = 3,772 · 2020 | 1 row |
| Blood pressure | Grade B | Improved | Meta-analysis of 33 trials · n = 2,427 · 2023 | 2 rows |
| Menopause | Grade B | No effect | RCT · n = 188 · 2012 | 1 row |
| Diabetes | Grade C | Mixed | Meta-analysis of 16 trials · n = 1,136 · 2025 | 1 row |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Total cholesterol, LDL and triglycerides | Improved | Grade B | Meta-analysis · n = 3,772 · 2020 Adults in 62 RCTs Form: flaxseed and flaxseed products · Dose: Varied across trials · Duration: Varied across trials Total cholesterol fell 5.4 mg/dL, LDL 4.2 mg/dL and triglycerides 9.4 mg/dL; HDL did not change. | 31899314 (opens PubMed)Source [5] |
| Systolic and diastolic blood pressure | Improved | Grade B | Meta-analysis · n = 2,427 · 2023 Adults in 33 trials (43 arms) of flaxseed products Form: whole or milled flaxseed, oil, lignan extracts · Dose: Varied; larger effects at 30 g/day or more of flaxseed · Duration: Varied; larger effects beyond 20 weeks Systolic BP fell 3.19 mmHg (95% CI −4.15 to −2.24) and diastolic 2.61 mmHg (−3.27 to −1.94). Effects were bigger in people with hypertension, at 30 g/day or more and in trials over 20 weeks. | 36622248 (opens PubMed)Source [2] |
| Menopausal hot flashes | No effect | Grade B | RCT · n = 188 · 2012 Postmenopausal women with or without breast cancer (US, North Central Cancer Treatment Group) Form: flaxseed bar · Dose: 410 mg lignans/day · Duration: 6 weeks Hot flash scores fell 4.9 points with flaxseed and 3.5 with placebo (p=0.29); about a third in each group halved their scores. | 21900849 (opens PubMed)Source [7] |
| Blood pressure in hypertensive patients with peripheral artery disease | Improved | Grade B | RCT · n = 110 · 2013 Adults with peripheral artery disease, many with hypertension (Canada) Form: milled flaxseed baked into foods · Dose: 30 g/day · Duration: 6 months Systolic BP was about 10 mmHg and diastolic about 7 mmHg lower than placebo; patients starting at 140 mmHg or more saw a 15 mmHg systolic drop. Body weight did not differ. | 24126178 (opens PubMed)Source [4] |
| Weight, blood pressure and lipids in people with diabetes | Mixed | Grade C | Meta-analysis · n = 1,136 · 2025 Adults with diabetes in 16 trials Form: flaxseed products · Dose: Varied across trials · Duration: Varied across trials Weight, waist circumference and triglycerides improved, but BMI, systolic and diastolic blood pressure, total cholesterol, LDL and HDL did not change significantly. | 40499336 (opens PubMed)Source [8] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Ground or milled flaxseed | Varies[1][4] | Milling lets the body reach the ALA and lignans; in a 6-month trial plasma ALA and enterolignans rose 2- to 50-fold on 30 g/day.[4] | Higher amounts can cause bloating, fullness and diarrhea.[1] | Blood-pressure trials (30 g/day); glucose subgroup effects were seen only with whole flaxseed |
| Flaxseed oil | Varies[1] | Supplies ALA but none of the fiber and little of the lignans.[1] | Probably safe short-term (up to 6 months) in limited amounts.[1] | Included in pooled blood-pressure and lipid analyses; did not show weight benefits |
| Flaxseed lignan extract | Varies[7] | Concentrated lignans; no human absorption data in our sources.[7] | GI symptoms were similar to placebo in a 6-week trial.[7] | Hot-flash trial (410 mg lignans/day) |
| Raw or unripe flaxseed (avoid) | Varies[1] | Not applicable.[1] | May contain potentially toxic compounds.[1] | Not studied; avoid |
Studied doses
Doses studied in human trials ranged from 410 mg/day of flax lignans to 30 g/day of milled flaxseed. The clearest blood-pressure trial used 30 g/day of milled flaxseed for 6 months, pooled analyses found larger effects at 30 g/day or more for over 20 weeks, and the hot-flash trial used 410 mg/day of lignans for 6 weeks.[2][4][7]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Medicines
- Anticoagulants and antiplatelet drugsNIH fact sheetTheoretical risk of added bleeding effect; not confirmed in trials. Check with a clinician before combining.[1]
Who should be careful
- Raw or unripe flaxseed
- Raw or unripe seeds may contain potentially toxic compounds; use mature, processed seed.[1]
- Pregnancy
- Some studies suggest flaxseed may be unsafe in pregnancy, though the evidence is not conclusive; safety while breastfeeding is unknown.[1]
- Blood thinners
- There is a theoretical interaction with anticoagulant and antiplatelet drugs.[1]
- Expecting hot-flash relief
- A 188-woman phase III trial found 410 mg/day of lignans did no better than placebo.[7]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Safety
Flaxseed is a common food and looks safe short-term; digestive upset is the usual problem.
- GI effects
- Higher doses can cause bloating, fullness and diarrhea; these also occurred on placebo in the hot-flash trial.[1][7]
- Short-term use
- Limited amounts of flaxseed, lignan extract or oil may be safe for up to 6 months.[1]
- Pregnancy
- Evidence on pregnancy is not conclusive, and some studies suggest possible harm.[1]
How to read the label
- Label dose vs clinical doseBlood-pressure benefits were clearest at 30 g/day of ground flaxseed, about 3 to 4 tablespoons. Flaxseed-oil softgels of 1 g supply ALA but not the fiber or most of the lignans.[2][4]
- Ground beats whole for most outcomesThe blood-pressure trial used milled seed, and in the glucose meta-analysis benefits appeared only with whole flaxseed products, not oil or lignan extracts.[4][6]
- Oil, lignans and seed are not interchangeableResults for one flaxseed product (seed, oil or lignan extract) do not transfer to the others.[1][7]
Cost per studied dose, without the sales pitch
Compare any product you already have by the amount it delivers, not by capsule count or front-of-pack weight.
Cost per studied dose
Enter the price, servings and the amount per serving from your label.
Frequently asked questions
Does flaxseed lower blood pressure?
Modestly. Across 33 trials systolic pressure fell about 3 mmHg, with bigger drops in people with hypertension, at 30 g/day or more and after 20 weeks; an earlier 14-trial analysis found about 1.8 mmHg.[2][3]
How much ground flaxseed should I use?
Trials that showed the clearest blood-pressure effects used about 30 g/day of milled flaxseed, roughly 3 to 4 tablespoons.[2][4]
Does flaxseed lower cholesterol?
Slightly. Across 62 RCTs LDL fell about 4 mg/dL and triglycerides about 9 mg/dL, with no change in HDL.[5]
Does flaxseed help hot flashes?
No. A 188-woman phase III trial found a flax lignan bar did no better than placebo over 6 weeks.[7]
Is flaxseed oil as good as ground flaxseed?
Not for every outcome. Oil supplies ALA but not the fiber or lignans, and the glucose benefits in pooled trials were seen only with whole flaxseed.[1][6]
Is flaxseed safe?
It is a common food and looks safe short-term. Higher doses cause bloating and diarrhea, raw or unripe seeds should be avoided, and use in pregnancy may be unsafe.[1]
Sources
- [1]Flaxseed and Flaxseed Oil: Usefulness and Safety (last updated February 2025). NIH National Center for Complementary and Integrative Health, 2025. fact-sheet
- [2]Effect of flaxseed supplementation on blood pressure: a systematic review, and dose-response meta-analysis of randomized clinical trials.. Food Funct, 2023. meta-analysis
- [3]Flaxseed consumption may reduce blood pressure: a systematic review and meta-analysis of controlled trials.. J Nutr, 2015. meta-analysis
- [4]Potent antihypertensive action of dietary flaxseed in hypertensive patients.. Hypertension, 2013. RCT
- [5]Effect of flaxseed supplementation on lipid profile: An updated systematic review and dose-response meta-analysis of sixty-two randomized controlled trials.. Pharmacol Res, 2020. meta-analysis
- [6]Flaxseed supplementation on glucose control and insulin sensitivity: a systematic review and meta-analysis of 25 randomized, placebo-controlled trials.. Nutr Rev, 2018. meta-analysis
- [7]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. RCT
- [8]The effect of flaxseed supplementation on anthropometric indices, blood pressure, and lipid profile in diabetic patients: A GRADE-assessed systematic review and meta-analysis of randomized controlled trials.. Diabetes Metab Syndr, 2025. meta-analysis
- [9]The effect of flaxseed supplementation on body weight and body composition: a systematic review and meta-analysis of 45 randomized placebo-controlled trials.. Obes Rev, 2017. meta-analysis
What changed
- First draft. Every PMID checked against NCBI E-utilities esummary (title and year taken from the record) and abstracts read for the cited rows.
- Adversarial review pass: every evidence row re-read against its PubMed abstract; pooled totals and effect sizes copied from the abstracts. Retraction and expression-of-concern check run on all 8 PMIDs via PubMed records: none flagged. Page set indexable.