Flaxseed Oil and Omega-6 Oils: Benefits, Forms, Dosing, and Side Effects

Flaxseed oil and the omega-6-rich seed oils — evening primrose, borage, black currant, and hemp — are among the most widely consumed plant-based fatty acid supplements. This comprehensive guide covers the evidence for ALA (alpha-linolenic acid) and GLA (gamma-linolenic acid), the two key fatty acids found in these oils, including their effects on cardiovascular health, skin conditions, inflammatory disorders, and more. It also covers recommended dosing, safety concerns, drug interactions, and the best dietary sources.

Table of Contents

• Overview
• Forms and Bioavailability
• Evidence for Benefits
• Recommended Dosing
• Safety and Side Effects
• Drug Interactions
• Dietary Sources
• References

Overview

Flaxseed oil and the omega-6-rich seed oils — evening primrose, borage, black currant, and hemp — are among the most widely consumed plant-based fatty acid supplements. They provide two distinct categories of polyunsaturated fatty acids: alpha-linolenic acid (ALA), an omega-3 fatty acid, and gamma-linolenic acid (GLA), an omega-6 fatty acid. Both are considered "good" fats, as opposed to saturated fats that may increase cardiovascular risk [1][2].

ALA (Alpha-Linolenic Acid) is an essential omega-3 fatty acid — meaning the body cannot manufacture it and must obtain it from the diet. Flaxseed (also known as linseed, Linum usitatissimum) contains among the highest concentrations of ALA of any plant seed: approximately 55% of flaxseed oil is ALA [1]. Chia seed oil has a similar concentration (58% ALA), though the seed itself has less total oil than flaxseed [1]. Other plant sources include hemp seed oil (19% ALA), black currant seed oil (13% ALA), soybean oil, canola oil, and walnuts [1].

From ALA, the body has a limited ability to manufacture two other critically important omega-3 fatty acids — EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). However, this conversion is inefficient: it is estimated that only 5–10% of dietary ALA is converted to EPA, and approximately 2–5% is converted to DHA [1][3]. Conversion may be somewhat higher in young women and in vegans and non-fish-eating vegetarians [4][5]. A 2025 study of red blood cell fatty acid levels across a wide population of adults found that EPA levels were not substantially different among vegans, vegetarians, pesco-vegetarians, and non-vegetarians, though DHA levels were approximately 26% lower among vegans and vegetarians than non-vegetarians and 35% lower than among pesco-vegetarians [6].

Because of this limited conversion, consuming ALA-rich foods is not an effective strategy for substantially boosting blood levels of EPA or DHA. For example, despite increasing red blood cell ALA concentrations, adding one to two ounces of walnuts (containing approximately 11% ALA) to the daily diets of older adults for two years did not increase DHA or EPA concentrations or omega-3 index compared to adults consuming their usual diets [7].

GLA (Gamma-Linolenic Acid) is an omega-6 fatty acid. Unlike ALA, GLA is not strictly essential — the body ordinarily produces sufficient GLA from linoleic acid (LA), another omega-6 fatty acid found in corn, sunflower, safflower, soy, and peanut oils [1]. However, GLA production may be reduced in several conditions: advanced age, diabetes, high alcohol intake, eczema, excessive saturated fat intake, elevated cholesterol, and certain vitamin or mineral deficiencies [1]. In such cases, supplementation may be beneficial.

Seed oils from evening primrose (Oenothera biennis), borage (Borago officinalis), and black currant (Ribes nigrum) are among the few plant oils rich in GLA. Hemp seed oil also contains a small amount. All of these oils are additionally rich in linoleic acid [1].

It is important to distinguish between flaxseed oil and whole flaxseeds. Flaxseeds themselves contain fiber and lignans — phytoestrogens that may have additional health effects including potential benefits for cancer prevention, cholesterol lowering, and menopausal symptoms. Flaxseed oil contains little or no lignans because lignans are bound to the fiber, which is lost when the oil is pressed [1]. Some specially processed flaxseed oils have lignans reintroduced after pressing.

Forms and Bioavailability

ALA Sources

The primary supplement sources of ALA differ substantially in their fatty acid profiles and practical characteristics:

Oil Source	ALA Content	LA Content	Other Notable Fatty Acids	Notes
Flaxseed oil	40–60%	~15%	Minimal GLA	Most concentrated plant source of ALA. ~7,600 mg ALA per tablespoon [1]
Chia seed oil	~58%	~20%	Minimal GLA	Similar ALA concentration to flaxseed but seeds have less total oil [1]
Hemp seed oil	~19%	~57%	~2–4% GLA, ~1% SDA	Also contains small amounts of GLA and stearidonic acid [1]
Black currant seed oil	~13%	~47%	15–20% GLA, ~1% SDA	Dual source of both ALA and GLA [1]
Echium oil	Varies	~15%	~12% SDA, ~10% GLA	Contains stearidonic acid (SDA), which converts to EPA more efficiently than ALA [8]
Walnut	~11%	~58%	Minimal GLA	Common dietary source; walnuts provide ~2,500 mg ALA per ounce [1][7]

Conversion of ALA to EPA and DHA: The conversion pathway proceeds through a series of enzymatic desaturation and elongation steps: ALA → stearidonic acid (SDA) → EPA → DPA → DHA. The rate-limiting step is the initial delta-6-desaturase enzyme, which is also used by the omega-6 pathway (LA → GLA → DGLA → arachidonic acid), creating competition between omega-3 and omega-6 substrates [1][3].

A 2025 study in healthy adults (ages 18–70) demonstrated that taking flaxseed oil containing 3,000 mg of ALA daily for nine months produced modest increases in red blood cell omega-3 levels. Those with low baseline EPA levels — most of whom followed a vegan diet — showed significantly greater increases than those starting with higher EPA levels: EPA (+62.9% vs +13.0%), DHA (+27.0% vs +7.6%), and DPA (+41.9% vs +22.3%) [9]. This suggests that flaxseed oil supplementation may be most impactful for individuals with very low omega-3 status, such as those following vegan or vegetarian diets.

Stearidonic acid (SDA) from echium oil, hemp seed oil, and black currant seed oil bypasses the rate-limiting delta-6-desaturase step, making it more efficiently converted to EPA than ALA. Daily supplementation with 15 grams of echium oil (taken in divided doses with meals) has been shown to significantly increase blood EPA levels, though not DHA [10]. One clinical study found that 17 grams per day of echium oil had a triglyceride-lowering effect similar to EPA from fish oil (17 grams of fish oil containing 1,900 mg EPA daily). Unlike fish oil, however, echium oil also lowered total and LDL cholesterol [11].

GLA Sources

GLA concentration varies substantially across the common supplement oils:

Oil Source	GLA Content	GLA per Tablespoon	Other Notable Features
Borage oil	17–25%	~3,000 mg	Highest GLA concentration. Most efficient way to obtain high-dose GLA [1]
Black currant oil	15–20%	~2,500 mg	Also contains 12–14% ALA — unique dual omega-3/omega-6 source [1]
Evening primrose oil	7–10%	~1,200 mg	Most popular and widely available GLA source despite lower concentration [1]
Hemp seed oil	2–4%	~400 mg	Low GLA content; better known as an ALA source [1]

GLA Metabolism: In the body, GLA is converted to dihomo-gamma-linolenic acid (DGLA), which binds to cyclooxygenase (COX) and lipoxygenase (LOX) enzymes and is converted to anti-inflammatory metabolites — 1-series prostaglandins and 15-HETrE [12]. However, DGLA can also be further converted to arachidonic acid (AA), which is a precursor to pro-inflammatory metabolites (2-series prostaglandins, 4-series leukotrienes). These conflicting pathways may partially explain the weak or inconsistent clinical evidence for GLA in inflammatory conditions [12].

Product Considerations

When selecting supplements, several practical factors are important [1]:

• Label specificity: Products vary significantly in amounts and ratios of fatty acids. Watch for "complex," "formula," or "blend" products that do not specify the exact amounts of GLA and ALA.
• Plant part used: Some black currant supplements are made from the "fruit" rather than the seed, which may contain no oil at all.
• Antioxidant preservation: Many products contain added vitamin E or other antioxidants to prevent rancidity, though this does not guarantee freshness.
• Storage: Because they are unsaturated fats, ALA, GLA, and LA are damaged by exposure to heat, light, and oxygen. These oils should be stored in a cool, dry place in well-sealed, opaque containers and should not be used for cooking [1].
• Saturated fat: All seed oils in this category contain some saturated fat (6–11%), though far less than coconut oil (91%) or palm kernel oil (85%) [1].
• Measurement conversion: One tablespoon of any of these oils is 15 mL or approximately 14,000 mg (14 grams), of which a percentage is ALA or GLA depending on the source [1].

Whole Flaxseed vs. Flaxseed Oil

Whole flaxseeds and milled (ground) flaxseeds offer advantages over flaxseed oil [1][2]:

• Fiber content: Flaxseeds are a rich source of both soluble and insoluble fiber, which contributes to digestive health and may have independent cholesterol-lowering effects.
• Lignans: Whole flaxseeds contain high levels of secoisolariciresinol diglucoside (SDG), a lignan precursor that acts as a phytoestrogen. Lignans are absent from standard flaxseed oil (unless reintroduced after processing).
• Blood pressure effects: Whole milled flaxseed has demonstrated significant blood pressure reduction in clinical trials, an effect not seen with refined flaxseed oil alone (see Evidence section).
• Bioavailability of ALA from seeds: Whole flaxseeds must be chewed well or consumed as ground seeds to release the oil. Swallowing whole seeds will not provide the full benefit.

Evidence for Benefits

Cardiovascular Health — ALA and Flaxseed

Cholesterol and Lipid Profile

The Mediterranean diet, which is high in ALA from plant sources, has been associated in observational studies with lower risk of coronary artery disease and possibly certain types of cancer [1]. However, isolated ALA supplementation has not been shown to significantly decrease cardiovascular disease risk on its own.

A study in Japan examined middle-aged men with elevated triglycerides (>100 mg/dL) who consumed 10 grams (10,000 mg) of flaxseed oil — containing 5,500 mg of ALA — with dinner for 12 weeks. The flaxseed oil led to a significant and meaningful decrease in small dense LDL cholesterol (sdLDL), the form of LDL most strongly associated with plaque formation and cardiovascular disease. However, flaxseed oil did not produce statistically significant changes in total cholesterol, total LDL, or triglycerides. Compared to the same amount of corn oil, flaxseed oil appeared more likely to lower total cholesterol, total LDL, and apoB, but was also more likely to lower HDL "good" cholesterol [13].

Other studies have failed to show improved triglycerides from ALA supplementation [46]. However, one study among healthy adults with normal triglyceride levels found that flaxseed oil providing 6 grams of ALA per day for one month significantly decreased triglyceride levels by 20% in younger adults (ages 18–29) but not in older adults (ages 45–69) [15].

Chia seeds, another ALA source, can modestly increase blood EPA levels (but not DHA) and have not been shown to improve risk factors for cardiovascular disease [16].

Blood Pressure

Flaxseed oil alone was not found to help lower blood pressure in people with high-normal blood pressure or stage 1 hypertension. In this study, participants consumed 5 grams of refined, cold-pressed flaxseed oil twice daily with meals (providing 4,700 mg per day of ALA) for three months. No significant blood pressure reduction was observed compared to a placebo of high-oleic sunflower oil [17].

Whole milled flaxseed, in contrast, has demonstrated significant blood pressure reduction. A controlled study in people with peripheral arterial disease (75% of whom had high blood pressure) found that consuming 1 ounce (30 grams) of milled flaxseed per day lowered blood pressure substantially. After 6 months, systolic blood pressure was approximately 10 mmHg lower and diastolic blood pressure was approximately 7 mmHg lower in the flaxseed group compared with placebo. Patients who started with a systolic blood pressure of at least 140 mmHg achieved reductions of 15 mmHg systolic and 7 mmHg diastolic [14]. These are clinically meaningful reductions, comparable to the effect of many antihypertensive medications.

Further analysis of these results led researchers to theorize that ALA in flaxseed may contribute to blood pressure reduction through inhibition of the enzyme soluble epoxide hydrolase (sEH), which reduces levels of oxylipin compounds that regulate vascular tone [18]. The additional components in whole flaxseed — fiber, lignans, and other bioactives — may work synergistically with ALA to produce the blood pressure effect that isolated flaxseed oil does not achieve.

Omega-3 Status in Vegans and Vegetarians

For individuals who do not consume fish or marine oils, flaxseed oil represents one of the few concentrated plant sources of omega-3 fatty acids. While ALA does not substitute for EPA and DHA in terms of their specific health benefits (particularly for triglyceride reduction, rheumatoid arthritis, and menstrual pain), it remains an essential fatty acid with its own dietary requirement [1].

A 2025 study demonstrated that flaxseed oil supplementation (3,000 mg ALA daily for 9 months) was more effective at raising EPA and DHA levels in individuals with low baseline omega-3 status — primarily vegans — than in those with higher starting levels [9]. This supports the use of flaxseed oil as a partial (though incomplete) omega-3 source for those who cannot or choose not to consume fish-derived omega-3s.

Gestational Diabetes

Research suggests that flaxseed oil supplements containing ALA might improve fasting glucose measures and insulin resistance in pregnant people with gestational diabetes [2][19]. A randomized, double-blind, placebo-controlled trial found that omega-3 fatty acids from flaxseed oil improved genetic and metabolic profiles in patients with gestational diabetes [19].

Weight Management

One clinical trial found that flaxseed mucilage powder (mixed with water) might support weight loss in adults with overweight or obesity [2][20]. However, flaxseed lignan extract and flaxseed oil supplements themselves do not appear to help with weight loss [2]. This finding aligns with the broader principle that the fiber and mucilage components of whole flaxseed provide benefits not found in the isolated oil.

ADHD

There is preliminary evidence that flaxseed oil might reduce hyperactivity and other symptoms of ADHD in children. The dosing used in preliminary studies was flaxseed oil providing 200 mg of ALA with 25 mg of vitamin C taken twice daily [1]. However, this evidence remains preliminary and requires confirmation in larger trials.

Dry Eye and Sjogren's Syndrome

Preliminary studies have suggested possible benefits of flaxseed oil in preventing dry eye in Sjogren's syndrome, an autoimmune condition. Dosing in studies has ranged from 1 to 2 grams daily of flaxseed oil [1].

Bipolar Disorder

Preliminary studies have suggested possible benefits of flaxseed oil as an adjunct to conventional treatments for bipolar disorder, though the evidence is early-stage [1].

Acne — GLA

A controlled study found that daily supplementation with the omega-6 fatty acid GLA significantly reduced the number and severity of acne lesions in men and women ages 18 to 33 with mild to moderate acne [21]. Participants received 2 capsules daily containing 400 mg total GLA from 2 grams of borage oil for 10 weeks. A separate group received omega-3 fatty acids (1,000 mg EPA and 1,000 mg DHA) for comparison, and a third group served as an untreated control.

Results after 10 weeks [21]:

• GLA group: 32.7% reduction in inflammatory acne lesions, 15.8% reduction in non-inflammatory lesions, 22% reduction in acne severity
• Omega-3 group: 42.6% reduction in inflammatory lesions, 19.6% reduction in non-inflammatory lesions, 29% reduction in severity
• Control group: No significant changes

Both the GLA and omega-3 supplementation groups showed statistically significant improvements compared to control. The omega-3 group showed numerically greater improvements, but both active treatments were effective.

Diabetic Neuropathy — GLA

The 2021 guidelines from the American Academy of Neurology state that GLA might be no more likely to improve pain from diabetic neuropathy than alpha-lipoic acid, which itself has only a very modest effect [22]. The typical dosing for diabetic neuropathy trials has been 400 to 600 mg of GLA daily (equivalent to approximately 4–6 grams of evening primrose oil or 2–3 grams of borage oil) [1].

Cyclic Mastalgia (Breast Pain) — GLA

GLA has been used in Europe to treat cyclic mastitis (breast inflammation associated with the menstrual cycle), although the evidence is weak [1]. Evening primrose oil alone does not appear to have much effect on cyclic mastalgia, and when given in combination with vitamin E, it has shown only slight or no benefit [23][24]. The typical dose used in mastalgia trials is 3 to 4 grams of evening primrose oil [1].

Eczema — GLA

Despite historical use in Europe, evidence indicates that GLA supplementation does not improve eczema. A comprehensive Cochrane review of data from 27 studies examining either evening primrose oil or borage oil for eczema found that neither oil was more effective than placebo [25].

Rheumatoid Arthritis — GLA

GLA may have some benefit in treating rheumatoid arthritis, particularly when used as purified GLA at higher doses and combined with traditional treatments [1]. The dosing range in rheumatoid arthritis studies has been wide, from 360 mg to as much as 2,000–3,000 mg of GLA from borage seed oil [1]. The anti-inflammatory mechanism involves DGLA's conversion to 1-series prostaglandins and 15-HETrE through the COX and LOX pathways [12].

Raynaud's Phenomenon — GLA

GLA may also have benefit in treating Raynaud's phenomenon, a condition causing reduced blood flow to the extremities, though the evidence is preliminary [1].

Dry Eye Syndrome — GLA

A 45-day study found that a combination of linoleic acid (28.5 mg twice daily) and GLA (15 mg twice daily) improved symptoms of aqueous-deficient keratoconjunctivitis sicca (dry eye syndrome) [26].

A longer 6-month study in postmenopausal women with dry eye used a supplement containing black currant seed oil and showed improvement in symptoms of irritation, better maintenance of corneal smoothness, and suppression of inflammation compared to placebo [27]. The daily dose consisted of 4 softgels providing 1,570 mg of black currant seed oil (240 mg GLA, 196 mg ALA, and 710 mg LA) in a formula that also included fish oil (126 mg EPA and 99 mg DHA) along with vitamins A, B6, C, and E [27].

Hair Loss — GLA / Black Currant Oil

Black currant seed oil is sometimes promoted for hair loss based on laboratory evidence showing that GLA can inhibit 5-alpha-reductase — the same enzyme targeted by the hair loss drug finasteride (Propecia, Proscar) [28]. An animal study showed that feeding black currant seed extract to menopausal rats slightly increased the number of hairs per hair follicle compared to control [29]. However, no clinical studies have evaluated black currant seed oil or GLA supplementation for hair growth or treating hair loss in humans [1].

The Omega-6 Controversy

A common concern is that the typical American diet already contains excessive omega-6 fatty acids (particularly LA from soybean, safflower, and corn oils) relative to omega-3 fatty acids. The ratio of omega-6 to omega-3 in the American diet may be as high as 14:1, while some authorities recommend a ratio of no more than 3:1 [1].

However, extensive evidence — including a systematic review of 30 randomized controlled trials — demonstrates that the omega-6 unsaturated fat linoleic acid (LA) does not, overall, have an inflammatory effect [30][31].

An important nuance comes from a study in Finnish men that found a common genetic variant in the FADS1 gene (which regulates fatty acid metabolism) can cause an inflammatory response to omega-6 fatty acids specifically in carriers of this variant. Adding a large amount (2–3 tablespoons) of LA-rich sunflower oil (62% LA) to the diet raised CRP (a marker of inflammation) only in those with the FADS1 genetic variant [32]. Approximately 33–42% of the population carries this variant, based on studies in China and Finland [33][34].

This finding suggests that while omega-6 fats are not inherently inflammatory for the general population, a substantial minority may have a genetically mediated inflammatory response to high omega-6 intake. This remains an active area of research.

Recommended Dosing

ALA — Adequate Intake (AI) Levels

The Institute of Medicine has established daily Adequate Intake levels for ALA and LA — the amounts needed in total from foods and supplements combined [1]:

Age/Sex	ALA (mg/day)
Children 1–3	700
Children 4–8	900
Males 9–13	1,200
Males 14+	1,600
Females 9–13	1,000
Females 14+	1,100
Pregnant women	1,400
Lactating women	1,300

LA Adequate Intake levels are approximately ten times higher than ALA. For example, the AI for adult women is 11,000–12,000 mg LA (13,000 mg during pregnancy or nursing), and for adult men aged 19–50 it is 17,000 mg [1].

Flaxseed Oil Dosing

• General supplementation: The typical serving is 1 to 2 tablespoons daily. One tablespoon of flaxseed oil provides approximately 7,000–7,600 mg of ALA [1].
• Capsule form: Flaxseed oil softgels typically provide 1,000–1,300 mg of oil per capsule, of which 500–700 mg is ALA. Multiple capsules are needed to match a tablespoon of liquid oil.
• For ADHD (preliminary): 200 mg of ALA with 25 mg of vitamin C taken twice daily [1].
• For Sjogren's syndrome (dry eye): 1 to 2 grams of flaxseed oil daily [1].

Whole Flaxseed Dosing

• For blood pressure: 30 grams (approximately 1 ounce or 2–3 tablespoons) of milled flaxseed per day, based on the trial by Rodriguez-Leyva et al. [14].
• General use: 1 tablespoon of ground flaxseed sprinkled on foods or taken with fluids 2 to 3 times a day [1].
• Important: Seeds must be chewed well or consumed in ground/milled form to release the oils. Whole seeds may pass through the digestive tract undigested [1].

GLA Dosing by Indication

Condition	GLA Dose	Evening Primrose Oil Equivalent	Borage Oil Equivalent
Diabetic neuropathy	400–600 mg/day	4–6 g/day	2–3 g/day
Cyclic mastalgia	~300–400 mg/day	3–4 g/day	1.5–2 g/day
Rheumatoid arthritis	360–3,000 mg/day	4–30 g/day	2–12 g/day
Acne	400 mg/day	4 g/day	2 g/day
Dry eye (combination)	30 mg/day (with LA)	—	—

Practical notes on GLA supplementation [1]:

• Treatment effects may take up to 6 months to reach full effect.
• It may be best to take these supplements in divided doses (twice or three times daily) rather than as a single daily dose.
• Because borage oil has the highest GLA concentration (17–25%), fewer capsules are needed to reach therapeutic GLA doses compared to evening primrose oil (7–10% GLA).

Safety and Side Effects

Common Side Effects

All products containing omega-3 or omega-6 fatty acids may cause mild gastrointestinal symptoms including nausea and diarrhea [1]. These symptoms may improve by taking smaller doses spread throughout the day, taking supplements with meals, or switching brands in case the current product is spoiled or rancid.

Higher doses of flaxseed or flaxseed oil supplements may cause uncomfortable digestive symptoms including bloating, fullness, and diarrhea [2].

Raw and Unripe Flaxseeds

Raw or unripe flaxseeds should not be consumed, as they may contain potentially toxic compounds including cyanogenic glycosides [2]. Cooking or processing eliminates this concern.

Seizure Risk with GLA

Those with seizure disorders should use caution when supplementing with GLA-containing oils (borage oil and evening primrose oil), as GLA may lower the seizure threshold [1].

Estrogenic Effects

Lignan precursors in some flaxseed products could potentially have weak estrogenic effects, affecting menstruation [1]. Standard flaxseed oil does not naturally contain lignan precursors, but some specially processed flaxseed oils have lignans reintroduced after pressing. Whole flaxseeds naturally contain high levels of lignan precursors [1].

Borage Plant — Pyrrolizidine Alkaloids

Parts of the borage plant (leaves and roots) contain pyrrolizidine alkaloids that are potentially hepatotoxic and carcinogenic [1]. However, pyrrolizidine alkaloids are not extracted with the seed oil, so borage oil supplements made from seeds are not expected to contain these compounds [1].

Prostate Cancer Risk — ALA

A study released in 2004 suggested that increased intakes of dietary ALA might increase the risk of advanced prostate cancer, although it was not associated with an increase in total cases of prostate cancer [35]. This finding has not been conclusively confirmed but warrants awareness, particularly for men consuming very high doses of ALA.

Cataract Risk — ALA

A 2007 study suggested that increased intakes of ALA might contribute to the development or progression of age-related cataracts [36]. This finding is from a single observational study and requires further investigation.

Allergic Reactions

Rarely, allergic reactions to flaxseed have been reported, including vomiting, shortness of breath, hives, and anaphylaxis [37][38][39]. Individuals with known flaxseed allergy should avoid both flaxseed and flaxseed oil products.

Fish Allergy Concerns with Combination Products

Some supplements combine seed oils with fish oils. People with fish or shellfish allergies should exercise caution with combination products, even those containing highly refined oils [1].

Pregnancy and Nursing

These products should be used cautiously during pregnancy and nursing as they may affect omega-3 metabolism, which is important for fetal and infant neurological development [1][2]. Evening primrose oil in particular may be associated with increased incidence of complications during labor and delivery [1]. Some studies suggest flaxseed use during pregnancy may be unsafe, though the evidence is not conclusive [2].

THC in Hemp Products

Hemp seed oil and hemp seeds may contain trace amounts of delta-9-THC. An analysis of three brands of hemp seed purchased from grocery stores in Canada found that all exceeded Canada's legal THC limit (10 mcg/g), with one brand 7- to 12-fold higher, such that only 30 grams (about 3 tablespoons) would provide 3.8 mg of THC [40]. There is also a case report of a man who consumed two tablespoons of cold-pressed hemp oil daily for four days and tested positive for THC on a standard drug test [41].

Due to these possibilities, some branches of the U.S. military — including the Army, Air Force, and Coast Guard — prohibit the use of any hemp-based products [1]. Under normal conditions, consuming 0.6 mg of THC would require approximately 8 tablespoons of hemp oil or 300 grams of hulled hemp seeds [42], but large variations in THC content across products make this estimate unreliable.

Drug Interactions

Anticoagulant and Antiplatelet Medications

Laboratory and animal studies, as well as preliminary research in people, suggest that flaxseeds and flaxseed oil have antiplatelet and anticoagulant (blood-thinning) effects [43][44]. Rare cases of increased bleeding and prolonged blood clotting time linked with flaxseed consumption have been reported in people taking blood thinners such as aspirin and warfarin [45].

People taking blood-thinning medications should consult with their physician before supplementing with flaxseed or flaxseed oil. Relevant medications include [1][2]:

• Aspirin
• Warfarin (Coumadin)
• Apixaban (Eliquis)
• Rivaroxaban (Xarelto)
• Betrixaban (Bevyxxa)

These products should also be used only under physician care by individuals with hemophilia, and their use should be stopped prior to surgical procedures [1].

General Drug Interaction Considerations

There are theoretical reasons to suspect that flaxseed or flaxseed oil might interact with other drugs beyond anticoagulants [2]. Anyone taking prescription medications should discuss flaxseed supplementation with their healthcare provider before starting.

Seizure Medications

Because GLA (from borage oil and evening primrose oil) may lower the seizure threshold, individuals taking anti-seizure medications should exercise particular caution and consult their neurologist before supplementing [1].

Dietary Sources

ALA-Rich Foods

Food	Serving	ALA Content (mg)
Flaxseed oil	1 tablespoon (14 g)	~7,600
Flaxseeds, ground	1 tablespoon (7 g)	~1,600
Chia seeds	1 ounce (28 g)	~5,100
Walnuts	1 ounce (28 g)	~2,500
Hemp seeds, hulled	3 tablespoons (30 g)	~2,600
Canola oil	1 tablespoon (14 g)	~1,280
Soybean oil	1 tablespoon (14 g)	~920
Edamame, cooked	1 cup	~280
Navy beans, cooked	1 cup	~320
Brussels sprouts, cooked	1 cup	~270

Flaxseeds are the most concentrated whole-food source of ALA. One tablespoon of ground flaxseed provides approximately 1,600 mg of ALA — already exceeding the daily Adequate Intake of 1,100 mg for adult women [1].

Additional sources include eggs produced from hens fed flaxseed and green leafy vegetables such as purslane [1].

GLA-Rich Foods

GLA is found in relatively few food sources. The primary sources are specialty seed oils available as supplements [1]:

Food/Oil	Serving	Approximate GLA (mg)
Borage oil	1 tablespoon (14 g)	~3,000
Black currant seed oil	1 tablespoon (14 g)	~2,500
Evening primrose oil	1 tablespoon (14 g)	~1,200
Hemp seed oil	1 tablespoon (14 g)	~400
Spirulina, dried	1 tablespoon (7 g)	~130

GLA is not widely available from common dietary sources, which is why supplementation is the primary means of obtaining therapeutic doses [1].

Practical Tips for Incorporating Flaxseed

• Ground vs. whole: Always use ground (milled) flaxseed rather than whole seeds. Whole seeds may pass through the digestive tract without being broken down, reducing ALA and lignan availability [1].
• Storage: Ground flaxseed should be refrigerated or frozen and used within a few weeks, as the oils oxidize rapidly once the seed coat is broken.
• Cooking: Flaxseed oil should not be used for cooking, as heat destroys its omega-3 fatty acids. Use it in salad dressings, smoothies, or drizzle it on cooked foods after cooking [1].
• Flaxseed oil capsules: For those who dislike the taste, softgel capsules provide ALA without the flavor of liquid oil, though multiple capsules are needed to match the ALA in a tablespoon of liquid oil.

References

1. ConsumerLab. "Flaxseed Oil and Omega-6 Fatty Acid Supplements Review (Evening Primrose, Borage, Black Currant, and Hemp Oils)." Accessed 2026. https://www.consumerlab.com/reviews/black-currant-borage-evening-primrose-flaxseed-and-hemp-oils-sources-of-ala-and-gla-omega-3-and-6-fatty-acids/flaxseed/

2. National Center for Complementary and Integrative Health (NCCIH). "Flaxseed and Flaxseed Oil." Updated February 2025. https://www.nccih.nih.gov/health/flaxseed-and-flaxseed-oil

3. Davis BC, Kris-Etherton PM. "Achieving optimal essential fatty acid status in vegetarians: current knowledge and practical implications." Am J Clin Nutr. 2003;78(3 Suppl):640S-646S. https://doi.org/10.1093/ajcn/78.3.640S

4. Burdge GC, Jones AE, Wootton SA. "Eicosapentaenoic and docosapentaenoic acids are the principal products of alpha-linolenic acid metabolism in young men." Br J Nutr. 2002;88(4):355-363. https://doi.org/10.1079/BJN2002662

5. Welch AA et al. "Dietary intake and status of n-3 polyunsaturated fatty acids in a population of fish-eating and non-fish-eating meat-eaters, vegetarians, and vegans." Am J Clin Nutr. 2010;92(5):1040-1051. https://doi.org/10.3945/ajcn.2010.29457

6. Harris WS et al. "Red blood cell fatty acid levels in vegans, vegetarians, pesco-vegetarians, and non-vegetarians." Prostaglandins Leukot Essent Fatty Acids (PLEFA). 2025.

7. Jehi T et al. "Effect of walnut supplementation on red blood cell omega-3 fatty acid levels in older adults." Br J Nutr. 2022. https://doi.org/10.1017/S0007114522000940

8. Botelho PB et al. "Effect of Echium oil compared with marine oils on cardiovascular risk markers in humans: a systematic review." Lipids Health Dis. 2013;12:121. https://doi.org/10.1186/1476-511X-12-121

9. Klein T et al. "Effects of flaxseed oil supplementation on red blood cell omega-3 fatty acid levels in healthy adults." Front Nutr. 2025. https://doi.org/10.3389/fnut.2025.1507037

10. Surette ME et al. "Dietary echium oil increases plasma and neutrophil long-chain (n-3) fatty acids and lowers serum triacylglycerols in hypertriglyceridemic humans." J Nutr. 2004;134(6):1406-1411. https://doi.org/10.1093/jn/134.6.1406

11. Kuhnt K et al. "Consumption of echium oil increases EPA and DPA in blood fractions more efficiently compared to linseed oil in humans." Lipids Health Dis. 2016;15:32. https://doi.org/10.1186/s12944-016-0199-2

12. Sergeant S, Rahbar E, Chilton FH. "Gamma-linolenic acid, dihomo-gamma-linolenic, eicosanoids and inflammatory processes." Eur J Pharmacol. 2016;785:77-86. https://doi.org/10.1016/j.ejphar.2016.04.020

13. Kawakami Y et al. "Flaxseed oil intake reduces serum small dense low-density lipoprotein concentrations in Japanese men." Nutr J. 2015;14:39. https://doi.org/10.1186/s12937-015-0023-2

14. Rodriguez-Leyva D et al. "Potent antihypertensive action of dietary flaxseed in hypertensive patients." Hypertension. 2013;62(6):1081-1089. https://doi.org/10.1161/HYPERTENSIONAHA.113.02094

15. Patenaude A et al. "Bioavailability of alpha-linolenic acid from flaxseed diets as a function of age." Eur J Clin Nutr. 2009;63(9):1123-1129. https://doi.org/10.1038/ejcn.2009.41

16. Ferreira CS et al. "Effect of chia seed consumption on cardiovascular risk factors in humans: a systematic review." Nutr Hosp. 2015;32(5):1909-1918. https://doi.org/10.3305/nh.2015.32.5.9394

17. Pieters DJ et al. "Effects of alpha-linolenic acid from flaxseed oil on blood pressure in subjects with high-normal blood pressure or mild hypertension." Br J Nutr. 2018. https://doi.org/10.1017/S0007114518002775

18. Caligiuri SP 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. 2014;64(1):53-59. https://doi.org/10.1161/HYPERTENSIONAHA.114.03179

19. Jamilian M et al. "The effects of n-3 fatty acids from flaxseed oil on genetic and metabolic profiles in patients with gestational diabetes mellitus." Br J Nutr. 2020;123(7):792-799. https://doi.org/10.1017/S0007114519003416

20. Bongartz U et al. "Flaxseed mucilage (IQP-LU-104) reduces body weight in overweight and moderately obese individuals." Obesity Facts. 2022;15(3):395-404. https://doi.org/10.1159/000522218

21. Jung JY et al. "Effect of dietary supplementation with omega-3 fatty acid and gamma-linolenic acid on acne vulgaris." Acta Derm Venereol. 2014;94(5):521-525. https://doi.org/10.2340/00015555-1802

22. Price R et al. "Oral and Topical Treatment of Painful Diabetic Polyneuropathy: Practice Guideline Update Summary." Neurology. 2022;98(1):31-43. https://doi.org/10.1212/WNL.0000000000013038

23. Kumari N et al. "Evening primrose oil for cyclic mastalgia: A systematic review." Cureus. 2024.

24. Pruthi S et al. "Vitamin E and evening primrose oil for management of cyclical mastalgia." Altern Med Rev. 2010;15(1):59-67. https://pubmed.ncbi.nlm.nih.gov/20359269/

25. Bamford JTM et al. "Oral evening primrose oil and borage oil for eczema." Cochrane Database Syst Rev. 2013;(4):CD004416. https://doi.org/10.1002/14651858.CD004416.pub2

26. Barabino S et al. "Systemic linoleic and gamma-linolenic acid therapy in dry eye syndrome with an inflammatory component." Cornea. 2003;22(2):97-101. https://doi.org/10.1097/00003226-200303000-00002

27. Sheppard JD et al. "Long-term supplementation with n-6 and n-3 PUFAs improves moderate-to-severe keratoconjunctivitis sicca." Cornea. 2013;32(10):1297-1304. https://doi.org/10.1097/ICO.0b013e318299549c

28. Liang T, Liao S. "Inhibition of steroid 5 alpha-reductase by specific aliphatic unsaturated fatty acids." Biochem J. 1992;285(Pt 2):557-562. https://doi.org/10.1042/bj2850557

29. Nanashima N et al. "Hair growth promotion effects of black currant seed extract." Molecules. 2019;24(8):1494. https://doi.org/10.3390/molecules24081494

30. Innes JK, Calder PC. "Omega-6 fatty acids and inflammation." Prostaglandins Leukot Essent Fatty Acids. 2018;132:41-48. https://doi.org/10.1016/j.plefa.2018.03.004

31. Su H et al. "Dietary linoleic acid intake and blood inflammatory markers: a systematic review and meta-analysis of randomized controlled trials." Food Funct. 2017;8(9):3091-3103. https://doi.org/10.1039/C7FO00433H

32. Lankinen MA et al. "A healthy Nordic diet alters the plasma lipidomic profile in adults with features of metabolic syndrome." Am J Clin Nutr. 2019. https://doi.org/10.1093/ajcn/nqz238

33. Zhu J et al. "FADS1 and FADS2 polymorphisms and fatty acid desaturation." J Lipid Res. 2013. https://doi.org/10.1194/jlr.M035378

34. Takkunen MJ et al. "FADS1, FADS2 gene variant and dietary fatty acid intake." Mol Nutr Food Res. 2016. https://doi.org/10.1002/mnfr.201500692

35. Brouwer IA et al. "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(4):919-922. https://doi.org/10.1093/jn/134.4.919

36. Lu M et al. "Dietary alpha-linolenic acid intake and risk of age-related cataract." J Am Coll Nutr. 2007;26(1):1-9. https://pubmed.ncbi.nlm.nih.gov/17353577/

37. Leon F et al. "Anaphylaxis to Linum usitatissimum (flaxseed/linseed)." Allergol Immunopathol (Madr). 2003;31(4):213-215. https://doi.org/10.1016/S0301-0546(03)79180-3

38. Alonso L et al. "Anaphylaxis caused by linseed (flaxseed) intake." J Allergy Clin Immunol. 1996;98(2):469-470. https://doi.org/10.1016/S0091-6749(96)70174-3

39. Harris KE, Unsworth DJ. "Flaxseed allergy." Ann Allergy Asthma Immunol. 2023. https://doi.org/10.1016/j.anai.2022.09.029

40. Yang Y et al. "Cannabis-related content in commercial hemp seeds." Cannabis Cannabinoid Res. 2018;3(1):110-113. https://doi.org/10.1089/can.2017.0045

41. Struempler RE et al. "A positive cannabinoids workplace drug test following the ingestion of commercially available hemp seed oil." J Anal Toxicol. 1997;21(4):283-285. https://doi.org/10.1093/jat/21.4.283

42. Leson G et al. "Evaluating the impact of hemp food consumption on workplace drug tests." J Anal Toxicol. 2001;25(8):691-698. https://doi.org/10.1093/jat/25.8.691

43. Nandish SKS et al. "Antiplatelet activity of flaxseed by in vitro and in vivo analysis." Pharmacogn Mag. 2018;14(57):S518-S523. https://doi.org/10.4103/pm.pm_420_17

44. Allman MA et al. "Supplementation with flaxseed oil versus sunflower seed oil in healthy young men consuming a low fat diet: effects on platelet composition and function." Eur J Clin Nutr. 1995;49(3):169-178. https://pubmed.ncbi.nlm.nih.gov/7774533/

45. Levy I et al. "Potential drug interactions with dietary and herbal supplements during hospitalization." Br J Clin Pharmacol. 2017;83(7):1483-1492. https://doi.org/10.1111/bcp.13243

46. Rodriguez-Leyva D et al. "The cardiovascular effects of flaxseed and its omega-3 fatty acid, alpha-linolenic acid." Can J Cardiol. 2010;26(9):489-496. https://doi.org/10.1016/S0828-282X(10)70455-4

47. Thompson LU, Mason JK. "Flaxseed." In: Coates PM, Betz JM, Blackman MR, et al., eds. Encyclopedia of Dietary Supplements. 2nd ed. New York, NY: Informa Healthcare; 2010:274-287.

48. Toulabi T et al. "Effects of flaxseed on blood pressure, body mass index, and total cholesterol in hypertensive patients." Explore (NY). 2022;18(4):438-445. https://doi.org/10.1016/j.explore.2021.07.001

49. Kuhnt K et al. "Evaluation of the impact of ruminant trans fatty acids on human health." J Nutr. 2014. (Echium oil comparison study with fish oil.)