Herb & supplement monograph

Flaxseed Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by ·Updated July 2026
What is this page for?

First and foremost: how Flaxseed interacts with medications. The heart of this page is the interaction list — every drug Flaxseed is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Flaxseed is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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Flaxseed Drug Interactions: The Bottom Line

From the HelloPharmacist Editorial Team · Updated July 2026

Based on the available evidence, the overall risk of a clinically significant Flaxseed drug interaction appears low for most people, though a few medication types deserve extra awareness. None of the listed interactions are rated major, and most rest on theoretical reasoning rather than proven effects in people.

Interactions deserving the most attention

The best-documented concern involves diabetes medications, since human studies suggest flaxseed can lower blood glucose, which could add to a drug's effect and raise the chance of low blood sugar. There is also some clinical evidence that flaxseed oil may reduce platelet clumping, so we give anticoagulant and antiplatelet drugs attention because even a small added effect matters with bleeding risk. Because daily flaxseed can modestly lower blood pressure over time, people taking blood pressure medications may notice an additive effect worth watching.

What the rest of the list means

The long list of interacting medications mostly reflects broad drug categories and theoretical concerns, not proven harm from each combination. For example, antibiotics might change how gut bacteria process flaxseed's natural compounds, and flaxseed's plant lignans could in theory compete with estrogens, but neither effect has been clearly shown to matter in people. In short, moderate ratings here signal caution and awareness rather than known danger.

Check your medications against Flaxseed

Based on HelloPharmacist’s Flaxseed interaction data and reviewed under our editorial standards.

Interaction report

Drugs that interact with Flaxseed

597 medications have a known interaction with Flaxseed, graded by severity. Select any drug for the full evidence-based detail.

2,830 drugs
AbciximabReoPro
Moderate Anticoagulant/antiplatelet Drugs

Theoretically, using flaxseed in combination with anticoagulant or antiplatelet drugs might have additive effects and increase the risk of bleeding.

Read the full Flaxseed + Abciximab interaction
AbrocitinibCibinqo
Moderate Anticoagulant/antiplatelet Drugs

Theoretically, using flaxseed in combination with anticoagulant or antiplatelet drugs might have additive effects and increase the risk of bleeding.

Read the full Flaxseed + Abrocitinib interaction Abrocitinib drug page: uses, dosage & side effects
AcarboseGlucobay, Prandase, Precose
Moderate Antidiabetes Drugs

Theoretically, flaxseed might have additive effects when used with antidiabetes drugs and increase the risk for hypoglycemia.

Read the full Flaxseed + Acarbose interaction Acarbose drug page: uses, dosage & side effects
AcebutololRhotral, Sectral
Moderate Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Read the full Flaxseed + Acebutolol interaction Acebutolol drug page: uses, dosage & side effects
AcenocoumarolSintrom
Moderate Anticoagulant/antiplatelet Drugs

Theoretically, using flaxseed in combination with anticoagulant or antiplatelet drugs might have additive effects and increase the risk of bleeding.

Read the full Flaxseed + Acenocoumarol interaction
Acetaminophen, AspirinGemnisyn
Moderate Anticoagulant/antiplatelet Drugs

Theoretically, using flaxseed in combination with anticoagulant or antiplatelet drugs might have additive effects and increase the risk of bleeding.

Read the full Flaxseed + Acetaminophen, Aspirin interaction
Acetaminophen, Aspirin, CaffeineExcedrin, Excedrin Extra Strength, Excedrin Migraine
Moderate Anticoagulant/antiplatelet Drugs

Theoretically, using flaxseed in combination with anticoagulant or antiplatelet drugs might have additive effects and increase the risk of bleeding.

Read the full Flaxseed + Acetaminophen, Aspirin, Caffeine interaction
Acetaminophen, IbuprofenCombogesic
Moderate Anticoagulant/antiplatelet Drugs

Theoretically, using flaxseed in combination with anticoagulant or antiplatelet drugs might have additive effects and increase the risk of bleeding.

Read the full Flaxseed + Acetaminophen, Ibuprofen interaction
AcetazolamideAk-Zol, Diamox
Moderate Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Read the full Flaxseed + Acetazolamide interaction Acetazolamide drug page: uses, dosage & side effects
AcetohexamideDymelor
Moderate Antidiabetes Drugs

Theoretically, flaxseed might have additive effects when used with antidiabetes drugs and increase the risk for hypoglycemia.

Read the full Flaxseed + Acetohexamide interaction
Acetylsalicylic AcidEntrophen
Moderate Anticoagulant/antiplatelet Drugs

Theoretically, using flaxseed in combination with anticoagulant or antiplatelet drugs might have additive effects and increase the risk of bleeding.

Read the full Flaxseed + Acetylsalicylic Acid interaction Acetylsalicylic Acid drug page: uses, dosage & side effects
AlbiglutideTanzeum
Moderate Antidiabetes Drugs

Theoretically, flaxseed might have additive effects when used with antidiabetes drugs and increase the risk for hypoglycemia.

Read the full Flaxseed + Albiglutide interaction
AliskirenTekturna
Moderate Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Read the full Flaxseed + Aliskiren interaction Aliskiren drug page: uses, dosage & side effects
AlogliptinNesina
Moderate Antidiabetes Drugs

Theoretically, flaxseed might have additive effects when used with antidiabetes drugs and increase the risk for hypoglycemia.

Read the full Flaxseed + Alogliptin interaction Alogliptin drug page: uses, dosage & side effects
Alogliptin, MetforminKazano
Moderate Antidiabetes Drugs

Theoretically, flaxseed might have additive effects when used with antidiabetes drugs and increase the risk for hypoglycemia.

Read the full Flaxseed + Alogliptin, Metformin interaction
Alogliptin, PioglitazoneOseni
Moderate Antidiabetes Drugs

Theoretically, flaxseed might have additive effects when used with antidiabetes drugs and increase the risk for hypoglycemia.

Read the full Flaxseed + Alogliptin, Pioglitazone interaction
Alteplase, TpaActilyse, Activase
Moderate Anticoagulant/antiplatelet Drugs

Theoretically, using flaxseed in combination with anticoagulant or antiplatelet drugs might have additive effects and increase the risk of bleeding.

Read the full Flaxseed + Alteplase, Tpa interaction
Aluminum Hydroxide, Aspirin, Codeine Phosphate, Magnesium HydroxideAscriptin Codeine #2
Moderate Anticoagulant/antiplatelet Drugs

Theoretically, using flaxseed in combination with anticoagulant or antiplatelet drugs might have additive effects and increase the risk of bleeding.

Read the full Flaxseed + Aluminum Hydroxide, Aspirin, Codeine Phosphate, Magnesium Hydroxide interaction
Aluminum Hydroxide, Aspirin, Magnesium HydroxideAscriptin
Moderate Anticoagulant/antiplatelet Drugs

Theoretically, using flaxseed in combination with anticoagulant or antiplatelet drugs might have additive effects and increase the risk of bleeding.

Read the full Flaxseed + Aluminum Hydroxide, Aspirin, Magnesium Hydroxide interaction Aluminum Hydroxide, Aspirin, Magnesium Hydroxide drug page: uses, dosage & side effects
AmbrisentanLetairis, Volibris
Moderate Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Read the full Flaxseed + Ambrisentan interaction Ambrisentan drug page: uses, dosage & side effects
AmikacinAmikin, Arikayce
Moderate Antibiotic Drugs

Theoretically, antibiotics might interfere with the metabolism of flaxseed constituents, which could potentially alter the effects of flaxseed.

Read the full Flaxseed + Amikacin interaction Amikacin drug page: uses, dosage & side effects
AmilorideAmilamont, Midamor
Moderate Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Read the full Flaxseed + Amiloride interaction Amiloride drug page: uses, dosage & side effects
Amiloride, HydrochlorothiazideAmil-Co, Amilzide, Moduret 25, Moduretic
Moderate Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Read the full Flaxseed + Amiloride, Hydrochlorothiazide interaction Amiloride, Hydrochlorothiazide drug page: uses, dosage & side effects
AmlodipineNorliqva
Moderate Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Read the full Flaxseed + Amlodipine interaction Amlodipine drug page: uses, dosage & side effects
Amlodipine BenzoateKaterzia
Moderate Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Read the full Flaxseed + Amlodipine Benzoate interaction Amlodipine Benzoate drug page: uses, dosage & side effects
Amlodipine BesilateIstin
Moderate Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Read the full Flaxseed + Amlodipine Besilate interaction
Amlodipine BesylateNorvasc
Moderate Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Read the full Flaxseed + Amlodipine Besylate interaction Amlodipine Besylate drug page: uses, dosage & side effects
Amlodipine Besylate, BenazeprilLotrel
Moderate Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Read the full Flaxseed + Amlodipine Besylate, Benazepril interaction
Amlodipine, CelecoxibConsensi
Moderate Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Read the full Flaxseed + Amlodipine, Celecoxib interaction
Ammonium ChlorideAmmonium Chloride
Moderate Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.

Read the full Flaxseed + Ammonium Chloride interaction
Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

  • Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
  • Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
  • Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
  • No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

  • Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
  • Probable. Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • Possible. Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists
  • Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

  • Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
  • Each drug listed above links to the full report for that exact Flaxseed combination — clinical detail, likelihood, evidence level, and citations.
  • Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.
The big picture

The kinds of drugs Flaxseed affects

Every type of medication (drug category) Flaxseed is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 5 drug categories Flaxseed interacts with
Antibiotic DrugsAnticoagulant/antiplatelet DrugsAntidiabetes DrugsAntihypertensive DrugsEstrogens
Antibiotic Drugs

Theoretically, antibiotics might interfere with the metabolism of flaxseed constituents, which could potentially alter the effects of flaxseed.
Some potential benefits of flaxseed are thought to be due to its lignan content. Secoisolariciresinol diglucoside (SDG), a major lignan precursor, is found in high concentrations in flaxseed. SDG is converted by bacteria in the colon to the lignans enterolactone and enterodiol. Antibiotics alter the flora of the colon, which could theoretically alter the metabolism of flaxseed.

Likelihood Possible Evidence D
Anticoagulant/Antiplatelet Drugs

Theoretically, using flaxseed in combination with anticoagulant or antiplatelet drugs might have additive effects and increase the risk of bleeding.
Some clinical evidence suggests that the oil contained in flaxseed can decrease platelet aggregation.

Likelihood Possible Evidence B
Antidiabetes Drugs

Theoretically, flaxseed might have additive effects when used with antidiabetes drugs and increase the risk for hypoglycemia.
Some clinical research suggests that flaxseed can lower blood glucose levels.

Likelihood Probable Evidence B
Antihypertensive Drugs

Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.
Clinical research shows that daily flaxseed consumption, especially for longer than 12 weeks, modestly reduces blood pressure.

Likelihood Possible Evidence D
Estrogens

Theoretically, taking flaxseed might decrease the effects of estrogens.
Flaxseed contains lignans with mild estrogenic and possible antiestrogenic effects. The lignans seem to compete with circulating endogenous estrogen and might reduce estrogen binding to estrogen receptors, resulting in an anti-estrogen effect. It is unclear if this effect transfers to exogenously administered estrogens.

Likelihood Possible Evidence D
Monograph

Flaxseed: Uses, Safety & Side Effects

Medically reviewed by · Reviewed July 2026 ·
The bottom line

Flaxseed is a nutritious food rich in fiber, omega-3 fats (ALA), and plant compounds called lignans. It is most reliably helpful for constipation and may modestly lower cholesterol, but evidence for many other uses is mixed or limited. It is generally safe as a food, but talk to your pharmacist or doctor before using it as a supplement, especially if you are pregnant or breastfeeding.

Flaxseed
Scientific name
Linum usitatissimum
Family
Linaceae
Part used
Seeds and seed oil
Common forms
Whole seeds, ground meal, oil, capsules, powder
People commonly use it for
  • Constipation and digestive health
  • High cholesterol
  • Heart health
  • Menopausal symptoms
  • Blood sugar support

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance
OverallUse caution

Generally safe as a food, but drink plenty of water and start with small amounts to reduce bloating and gas.

PregnancyPossibly Unsafe

When used orally. Flaxseed can have mild estrogenic effects. Theoretically, this might adversely affect pregnancy; however, there is no reliable clini...

Read the full pregnancy detail
BreastfeedingInsufficient reliable information

Insufficient reliable information available; avoid using.

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Jump to a section

Overview

Flaxseed (also called linseed) comes from the flax plant, Linum usitatissimum, one of the oldest cultivated crops in the world. It is grown in many regions, including Canada, the United States, India, and parts of Europe, for both its seeds and its fibers.

The small, glossy seeds can be brown or golden. People use flaxseed as a food and as a dietary supplement. It is taken as whole seeds, ground meal (the form best absorbed by the body), oil, or capsules. Ground flaxseed is often added to cereal, smoothies, yogurt, and baked goods.

Flaxseed is valued because it is rich in fiber, plant-based omega-3 fatty acids, protein, and plant compounds called lignans.

How it works

Flaxseed contains several active components that may explain its possible effects:

  • Fiber: Flaxseed has both soluble and insoluble fiber. Soluble fiber may help bind cholesterol and slow digestion, while insoluble fiber adds bulk that helps move stool through the gut.
  • Omega-3 fatty acids (ALA): Flaxseed is rich in alpha-linolenic acid, a plant-based omega-3 that the body can partly convert into other omega-3s. These fats are studied for possible anti-inflammatory and heart-related effects.
  • Lignans: These plant compounds have weak estrogen-like activity and antioxidant properties.

Much of what we know about how these compounds work comes from laboratory and animal studies, so the real-world effects in people are not fully proven.

Effectiveness

Does Flaxseed work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by .

Evidence overview · 31 uses evaluated
7 Possibly effective 1 Leans ineffective 23 Insufficient evidence
How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.
2Likely EffectiveGood evidence, though not yet conclusive.
3Possibly EffectiveSome evidence suggests a benefit.
4Possibly IneffectiveSome evidence it may not help.
5Likely IneffectiveFairly strong evidence it doesn’t help.
6IneffectiveStrong evidence it doesn’t work.
7Insufficient Reliable Evidence to RateToo little research to say either way.
Possibly Effective Constipation
Rating & evidence shown verbatim from Natural Medicines

Oral flaxseed is a bulk forming laxative that helps to relieve constipation.

Possibly Effective Diabetes
Rating & evidence shown verbatim from Natural Medicines

Oral ground flaxseed modestly reduces blood glucose in patients with diabetes and pre-diabetes. It is unclear if oral whole flaxseed reduces blood glucose.

Possibly Effective Hypercholesterolemia
Rating & evidence shown verbatim from Natural Medicines

Oral whole and ground flaxseed modestly reduce lipid levels.

Possibly Effective Hypertension
Rating & evidence shown verbatim from Natural Medicines

Daily oral flaxseed consumption, especially for longer than 12 weeks, seems to modestly reduce blood pressure.

Possibly Effective Mastalgia
Rating & evidence shown verbatim from Natural Medicines

Oral flaxseed seems to reduce symptoms of cyclic mastalgia.

Possibly Effective Obesity
Rating & evidence shown verbatim from Natural Medicines

Oral flaxseed and flaxseed mucilage seem to modestly improve weight loss in patients who are obese or overweight. However, flaxseed lignan extract does not seem to be beneficial.

Possibly Effective Systemic lupus erythematosus (SLE) nephritis
Rating & evidence shown verbatim from Natural Medicines

Oral flaxseed might be beneficial for improving kidney function in SLE.

Possibly Ineffective Osteoporosis
Rating & evidence shown verbatim from Natural Medicines

Oral flaxseed does not seem to be beneficial in osteoporosis.

Also studied for 23 conditions — evidence insufficient to rate
Insufficient Reliable Evidence To Rate Acne
Rating & evidence shown verbatim from Natural Medicines

Although there is interest in using oral flaxseed for acne, there is insufficient reliable information about the clinical effects of flaxseed for this purpose.

Insufficient Reliable Evidence To Rate Benign prostatic hyperplasia (BPH)
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral flaxseed lignan improves symptoms of BPH.

Insufficient Reliable Evidence To Rate Breast cancer
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral flaxseed reduces the risk for breast cancer or the progression of breast cancer.

Insufficient Reliable Evidence To Rate Burning mouth syndrome
Rating & evidence shown verbatim from Natural Medicines

Flaxseed has only been evaluated in a mouthwash in combination with German chamomile; its effect when used alone is unclear.

Insufficient Reliable Evidence To Rate Cardiovascular disease (CVD)
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral flaxseed or flaxseed lignans reduce the development or progression of CVD.

Insufficient Reliable Evidence To Rate Chronic kidney disease (CKD)
Rating & evidence shown verbatim from Natural Medicines

Although there is interest in using oral flaxseed for CKD, there is insufficient reliable information about the clinical effects of flaxseed for this condition.

Insufficient Reliable Evidence To Rate Colorectal cancer
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral flaxseed reduces the risk of colorectal cancer.

Insufficient Reliable Evidence To Rate Endometrial cancer
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral flaxseed reduces the risk of endometrial cancer.

Insufficient Reliable Evidence To Rate Fatigue
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral ground flaxseed reduces fatigue in overweight children.

Insufficient Reliable Evidence To Rate Impaired glucose tolerance (prediabetes)
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral flaxseed is beneficial in prediabetes.

Insufficient Reliable Evidence To Rate Irritable bowel syndrome (IBS)
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral flaxseed improves IBS symptoms.

Insufficient Reliable Evidence To Rate Lung cancer
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral flaxseed reduces the risk of lung cancer.

Insufficient Reliable Evidence To Rate Menopausal symptoms
Rating & evidence shown verbatim from Natural Medicines

There is contradictory evidence about the effects of flaxseed for reducing menopausal symptoms.

Insufficient Reliable Evidence To Rate Metabolic syndrome
Rating & evidence shown verbatim from Natural Medicines

Small studies suggest that oral flaxseed is beneficial for metabolic syndrome.

Insufficient Reliable Evidence To Rate Nonalcoholic fatty liver disease (NAFLD)
Rating & evidence shown verbatim from Natural Medicines

Small clinical studies suggest that oral flaxseed may modestly reduce markers of liver disease progression in patients with NAFLD.

Insufficient Reliable Evidence To Rate Osteoarthritis
Rating & evidence shown verbatim from Natural Medicines

It is unclear if topical flaxseed is beneficial in patients with osteoarthritis.

Insufficient Reliable Evidence To Rate Peripheral arterial disease (PAD)
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral flaxseed is beneficial in patients with PAD.

Insufficient Reliable Evidence To Rate Pharyngitis
Rating & evidence shown verbatim from Natural Medicines

Although there is interest in using oral flaxseed for pharyngitis, there is insufficient reliable information about the clinical effects of flaxseed for this purpose.

Insufficient Reliable Evidence To Rate Polycystic ovary syndrome (PCOS)
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral flaxseed is beneficial in patients with PCOS.

Insufficient Reliable Evidence To Rate Prostate cancer
Rating & evidence shown verbatim from Natural Medicines

Small clinical studies suggest that oral flaxseed may modestly improve biomarkers of prostate cancer.

Insufficient Reliable Evidence To Rate Radiation-induced pneumonitis
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral flaxseed is beneficial for preventing radiation-induced pneumonitis in patients with non-small cell lung cancer (NSCLC).

Insufficient Reliable Evidence To Rate Rheumatoid arthritis (RA)
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral flaxseed is beneficial in patents with RA.

Insufficient Reliable Evidence To Rate Ulcerative colitis
Rating & evidence shown verbatim from Natural Medicines

It is unclear if oral flaxseed is beneficial in patients with ulcerative colitis.

Source & disclaimer. Effectiveness ratings and evidence summaries are provided by Natural Medicines (Therapeutic Research Center) and shown as licensed. Where Natural Medicines hasn’t rated a use, HelloPharmacist’s pharmacists may add their own reviewed rating and evidence (each such entry is labeled). This is educational information, not medical advice — talk with your pharmacist or doctor before starting, stopping, or changing a supplement.

Safety & precautions

Flaxseed is widely eaten as a food and is generally considered safe for most adults when used in normal amounts. To lower the chance of side effects, increase your intake slowly and drink plenty of water.

Use extra caution if you:

  • Have a bowel narrowing or blockage, or trouble swallowing, since the fiber can swell and worsen blockage.
  • Have a hormone-sensitive condition, because lignans have weak estrogen-like effects (evidence is unclear, so talk to your doctor).
  • Are scheduled for surgery, since flaxseed may affect bleeding in some people.

Pregnancy: Eating flaxseed as a food is likely fine, but supplement doses may have hormone-like effects, so avoid them unless your doctor approves. Breastfeeding: There is not enough reliable safety information for supplement doses, so use caution. Avoid raw or unripe flaxseed, which may contain natural compounds that release small amounts of cyanide.

Side effects

The most common side effects come from its fiber content and include:

  • Bloating, gas, and stomach cramps
  • Loose stools or, if you don't drink enough water, constipation

These often improve if you start with a small amount and slowly increase it. Drinking enough fluid is important.

Rarely, some people are allergic to flaxseed and could have a serious reaction. Eating large amounts of raw or unripe flaxseed is not recommended because of natural cyanide-forming compounds. Stop and seek medical help if you have trouble breathing, swelling, or signs of a blockage such as severe belly pain.

Flaxseed: Reported Adverse Effects

Documented safety reports on Flaxseed from the evidence-graded Natural Medicines (TRC Healthcare) database, shown word-for-word from the licensed record.

Orally, flaxseed is usually well-tolerated.

Most Common Adverse Effects:

Orally: Bloating, diarrhea, gastrointestinal complaints.

Serious Adverse Effects (Rare):

Orally: Severe allergic reactions such as and anaphylaxis.

Reports by condition
Cancer Oncologic

Flaxseed contains alpha-linolenic acid (ALA). High dietary intake of ALA has been associated with increased risk for prostate cancer. However, ALA from plant sources, such as flaxseed, does not seem to increase this risk.

  1. Kolonel LN, Nomura AM, Cooney RV. Dietary fat and prostate cancer: current status. J Natl Cancer Inst 1999;91:414-28.
  2. Ramon JM, Bou R, Romea S, et al. Dietary fat intake and prostate cancer risk: a case-control study in Spain. Cancer Causes Control 2000;11:679-85.
  3. Giovannucci E, Rimm EB, Colditz GA, et al. A prospective study of dietary fat and risk of prostate cancer. J Natl Cancer Inst 1993;85:1571-9.
  4. De Stefani E, Deneo-Pellegrini H, Boffetta P, et al. Alpha-linolenic acid and risk of prostate cancer: a case-control study in Uruguay. Cancer Epidemiol Biomarkers Prev 2000;9:335-8.
  5. Brouwer IA, Katan MB, Zock PL. Dietary alpha-linolenic acid is associated with reduced risk of fatal coronary heart disease, but increased prostate cancer risk: a meta-analysis. J Nutr 2004;134:919-22.
  6. Laaksonen DE, Laukkanen JA, Niskanen L, et al. Serum linoleic and total polyunsaturated fatty acids in relation to prostate and other cancers: a population-based cohort study. Int J Cancer 2004;111:444-50..
Constipation Gastrointestinal

Integrating flaxseed in the diet can cause digestive symptoms similar to other sources of dietary fiber including bloating, fullness, flatulence, abdominal pain, diarrhea, constipation, dyspepsia, and nausea. Higher doses are likely to cause more gastrointestinal side effects. Flaxseed can significantly increase the number of bowel movements and the risk for diarrhea. Doses greater than 45 grams per day may not be tolerated for this reason. Metallic aftertaste and bowel habit deterioration have also been reported in a clinical trial.

There is some concern that taking large amounts of flaxseed could result in bowel obstruction due to the bulk forming laxative effects of flaxseed. Bowel obstruction occurred in one patient in a clinical trial. However, this is not likely to occur if flaxseed is consumed with an adequate amount of fluids.

  1. Dodin S, Lemay A, Jacques H, et al. The effects of flaxseed dietary supplement on lipid profile, bone mineral density, and symptoms in menopausal women: a randomized, double-blind, wheat germ placebo-controlled clinical trial. J Clin Endocrinol Metab 2005
  2. 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;17:3577-87.
  3. Thompson LU, Chen JM, Li T, et al. Dietary flaxseed alters tumor biological markers in postmenopausal breast cancer. Clin Cancer Res 2005;11:3828-35.
  4. Cockerell KM, Watkins AS, Reeves LB, et al. Effects of linseeds on the symptoms of irritable bowel syndrome: a pilot randomised controlled trial. J Hum Nutr Diet 2012;25:435-43.
  5. Colli MC, Bracht A, Soares AA, et al. Evaluation of the efficacy of flaxseed meal and flaxseed extract in reducing menopausal symptoms. J Med Food 2012;15:840-5.
  6. Simbalista RL, Sauerbronn AV, Aldrighi JM, Areas JA. Consumption of a flaxseed-rich food is not more effective than a placebo in alleviating the climacteric symptoms of postmenopausal women. J Nutr 2010;140:293-7.
  7. Patade A, Devareddy L, Lucas EA, et al. Flaxseed reduces total and LDL cholesterol concentrations in Native American postmenopausal women. J Womens Health (Larchmt) 2008;17:355-66.
  8. Bloedon LT, Balikai S, Chittams J, et al. Flaxseed and cardiovascular risk factors: results from a double blind, randomized, controlled clinical trial. J Am Coll Nutr 2008;27:65-74.
  9. Haidari F, Banaei-Jahromi N, Zakerkish M, Ahmadi K. The effects of flaxseed supplementation on metabolic status in women with polycystic ovary syndrome: a randomized open-labeled controlled clinical trial. Nutr J. 2020;19(1):8.
  10. Cunnane SC, Hamadeh MJ, Liede AC, et al. Nutritional attributes of traditional flaxseed in healthy young adults. Am J Clin Nutr 1995;61:62-8.
  11. Clark WF, Kortas C, Heidenheim P, et al. Flaxseed in lupus nephritis: a two-year nonplacebo-controlled crossover study. J Am Coll Nutr 2001;20:143-8.
  12. Clark WF, Parbtani A, Huff MW, et al. Flaxseed: a potential treatment for lupus nephritis. Kidney Int 1995;48:475-80.
DISCLAIMER: This tool is intended for informational purposes only, and should not be interpreted as specific medical advice. Patients should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.

Adverse-effects data: Natural Medicines, Therapeutic Research Center

Dosing

There is no single official dose for flaxseed, and the right amount depends on why you are using it and the form you choose. Ground (milled) flaxseed is generally better absorbed than whole seeds, which can pass through undigested.

The best approach is to follow the directions on the product label and start with a small amount, increasing slowly while drinking plenty of water. Take it with fluids, especially when using it for constipation.

Because doses and product strengths vary, check with your pharmacist or doctor before starting flaxseed as a supplement, particularly if you have a health condition or take medications.

Pregnancy & Breastfeeding

Flaxseed & Breastfeeding

Insufficient reliable information

Insufficient reliable information available; avoid using.

DISCLAIMER: This tool is intended for informational purposes only, and should not be interpreted as specific medical advice. Patients should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.

© 2026 Therapeutic Research Center

Pregnancy & lactation ratings: Natural Medicines, Therapeutic Research Center

References & further reading

The 37 references that drive our Flaxseed monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Kolonel LN, Nomura AM, Cooney RV. Dietary fat and prostate cancer: current status. J Natl Cancer Inst 1999;91:414-28. PubMed
  2. Ramon JM, Bou R, Romea S, et al. Dietary fat intake and prostate cancer risk: a case-control study in Spain. Cancer Causes Control 2000;11:679-85. PubMed
  3. Thompson LU, Rickard SE, Cheung F, et al. Variability in anticancer lignan levels in flaxseed. Nutr Cancer 1997;27:26-30. PubMed
  4. Nordstrom DC, Honkanen VE, Nasu Y, et al. Alpha-linolenic acid in the treatment of rheumatoid arthritis. A double-blind, placebo-controlled and randomized study: flaxseed vs. safflower seed. Rheumatol Int 1995;14:231-4. PubMed
  5. Cunnane SC, Ganguli S, Menard C, et al. High alpha-linolenic acid flaxseed (Linum usitatissimum): some nutritional properties in humans. Br J Nutr 1993;69:443-53.
  6. Clark WF, Parbtani A, Huff MW, et al. Flaxseed: a potential treatment for lupus nephritis. Kidney Int 1995;48:475-80. PubMed
  7. Cunnane SC, Hamadeh MJ, Liede AC, et al. Nutritional attributes of traditional flaxseed in healthy young adults. Am J Clin Nutr 1995;61:62-8. PubMed
  8. De Stefani E, Deneo-Pellegrini H, Boffetta P, et al. Alpha-linolenic acid and risk of prostate cancer: a case-control study in Uruguay. Cancer Epidemiol Biomarkers Prev 2000;9:335-8.
  9. Giovannucci E, Rimm EB, Colditz GA, et al. A prospective study of dietary fat and risk of prostate cancer. J Natl Cancer Inst 1993;85:1571-9. PubMed
  10. Clark WF, Kortas C, Heidenheim P, et al. Flaxseed in lupus nephritis: a two-year nonplacebo-controlled crossover study. J Am Coll Nutr 2001;20:143-8. PubMed
  11. Serraino M, Thompson LU. The effect of flaxseed supplementation on early risk markers for mammary carcinogenesis. Cancer Lett 1991;60:135-42. PubMed
  12. Rickard SE, Yuan YV, Thompson LU. Plasma insulin-like growth factor I levels in rats are reduced by dietary supplementation of flaxseed or its lignan secoisolariciresinol diglycoside. Cancer Lett 2000;161:47-55. PubMed
  13. Mousavi Y, Adlercreutz H. Enterolactone and estradiol inhibit each other's proliferative effect on MCF-7 breast cancer cells in culture. J Steroid Biochem Mol Biol 1992;41:615-9.. PubMed
  14. Adlercreutz H, Fotsis T, Bannwart C, et al. Determination of urinary lignans and phytoestrogen metabolites, potential antiestrogens and anticarcinogens, in urine of women on various habitual diets. J Steroid Biochem 1986;25:791-7.. PubMed
  15. Rose DP. Dietary fiber and breast cancer. Nutr Cancer 1990;13:1-8.. PubMed
Keep reading

This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Brand directory

Brands that make products with Flaxseed

101 brands in our database make a supplement containing Flaxseed.

Product directory

Supplement products with Flaxseed

268 products in our database contain Flaxseed. Open any to see its full ingredient list and every drug interaction we check.

100% Whey Cookies & Cream by GNC Pro Performance Powder 4.84 Pound(s) · 77.4 Ounce(s) · 2195.2 Gram(s) View ingredients & interactions Advanced Reds by BodSmith Powder 324.9 Gram(s) · 11.5 Ounce(s) View ingredients & interactions AdvoGreens Greens Powder Lemon by AdvoCare Powder 7 Ounce(s) · 200 Gram(s) View ingredients & interactions AdvoGreens Reds Powder Berry by AdvoCare Powder 7 Ounce(s) · 200 Gram(s) View ingredients & interactions BarnDad's FiberDX Flavorless by BarnDad Innovative Nutrition Powder 21.1 Oz(s) · 1.32 lb(s) · 600 Gram(s) View ingredients & interactions BarnDad's FiberDX German Chocolate by BarnDad Innovative Nutrition Powder 24.7 Ounce(s) · 1.54 Pound(s) · 700 Gram(s) View ingredients & interactions Battle Fuel by MusclePharm Capsule 126 Capsule(s) View ingredients & interactions BioCleanse Plus by Nutra BioGenesis Powder 1.606 Pound(s) · 731 Gram(s) View ingredients & interactions Black Seed Oil Blend with Pure Cold-Pressed Flax Seed Oil by Amazing Herbs Liquid 8 Fluid Ounce(s) · 240 mL View ingredients & interactions Blood Pressure Mixture by Hawaii Pharm Liquid 4 Fluid Ounce(s) · 120 mL View ingredients & interactions Blood Pressure Mixture Sugar Free by Herbal Terra Liquid 2 Fluid Ounce(s) · 60 mL View ingredients & interactions Blood Pressure Support by Hawaii Pharm Liquid 4 Fluid Ounce(s) · 120 mL View ingredients & interactions Blood Pressure Support Alcohol Free by Hawaii Pharm Liquid 4 Fluid Ounce(s) · 120 mL View ingredients & interactions Blood Pressure Support Non-Alcohol by Hawaii Pharm Liquid 4 Fluid Ounce(s) · 120 mL View ingredients & interactions CapraCleanse by Mt. Capra Other (e.g. Tea Bag) 180 Caplet(s) View ingredients & interactions Certified Organic High Lignan Flax Oil by Flora Liquid 17 Fluid Ounce(s) · 500 mL View ingredients & interactions Certified Organic High Lignan Flax Oil by Flora Liquid 8.5 fl. Oz. · 250 mL View ingredients & interactions Certified Organic High Lignan Flax Oil by Flora Liquid 17 fl. Oz. · 500 mL View ingredients & interactions Cleanse by Optimal Alpha Capsule 30 Capsule(s) View ingredients & interactions Colon Cleanse Detox by Thrive Naturals Capsule 60 Veggie Capsule(s) View ingredients & interactions Colon Normalizer by T/H/P/ Inc. Powder 150 Gram(s) View ingredients & interactions COLONIX Intestinal Cleanser by DrNatura Powder 360 Gram(s) · 12.7 Ounce(s) View ingredients & interactions Complete Shake Chai by Spectra Wellness Solutions Powder 2.91 lbs · 1320 Gram(s) · 44.6 Oz(s) View ingredients & interactions Complete Shake Chai by Elevation Health Powder 46.6 oz. · 1320 Gram(s) View ingredients & interactions
Pharmacist Counseling Corner

Flaxseed: Common Questions

What is Flaxseed used for, and does it work?
People use Flaxseed for many reasons, but the evidence varies by use. According to the Natural Medicines database, there is at least some clinical evidence supporting Flaxseed for Constipation, Diabetes, Hypercholesterolemia and Hypertension. For most other uses it has been studied for, the evidence is currently insufficient to rate. See the graded list on this page, and always confirm with your pharmacist or doctor.
Does Flaxseed interact with prescription medications?
Yes. We list 597 medications with a known interaction with Flaxseed. Use the checker above to see how Flaxseed interacts with a specific drug.
How are Flaxseed interactions rated?
Each interaction is graded major, moderate, or minor based on how clinically significant it is and the strength of the evidence behind it. Major interactions are the most serious and are best avoided, or used only under close professional supervision.
Is it safe to take Flaxseed with my medications?
It depends on the specific medication. Some combinations are fine, while others call for monitoring, timing changes, or should be avoided. Check your exact drug above and confirm with your pharmacist or doctor before starting, stopping, or changing anything.
Where does this Flaxseed interaction information come from?
Our interaction data is built on the Natural Medicines database — an evidence-graded reference for vitamins, herbs, and supplements — and is reviewed by licensed HelloPharmacist pharmacists, who may add clinical context.
What is Flaxseed used for?
People most commonly use Flaxseed for constipation and digestive health, and for modestly lowering cholesterol. It is also tried for heart health, menopausal symptoms, and blood sugar, but the evidence for these is weaker.
Should I use whole or ground Flaxseed?
Ground (milled) Flaxseed is usually better because whole seeds can pass through your body undigested. Grinding helps your body absorb the nutrients and beneficial compounds.
Is Flaxseed safe to take every day?
For most adults, Flaxseed is generally safe as a food when eaten in normal amounts with plenty of water. Start with a small amount to avoid bloating and gas, and check with your pharmacist if you have a health condition.
Can I take Flaxseed while pregnant or breastfeeding?
Eating Flaxseed as a food is likely fine, but supplement doses may have hormone-like effects and lack good safety data, so it is safest to avoid concentrated supplements unless your doctor approves.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

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Products that contain Flaxseed

A rotating sample of real supplements in our database that list Flaxseed — open any to see its full ingredients and every drug interaction we check.

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