In the US, nutraceuticals are marketed under the Dietary Supplement and Health Education Act of 1994 (DSHEA). Consequently, scientific data supporting claimed benefit(s) are not always available for nutraceuticals as they are for traditional pharmaceuticals since nutraceuticals are not regulated as drugs. Consumers should also note that rigid quality control standards are not required for nutraceuticals and substantial variability can occur in both the potency and the purity of these products. Monographs on nutraceuticals are included when reliable clinical data are available. The information presented below is condensed from the best clinical data we could find.
Flaxseed, Linum usitatissimum, is an annual plant cultivated in temperate and tropical regions worldwide traditionally used as a bulk laxative. Various species of the plant exist and all are equally useable for the medical purposes listed. The parts of the plant used include the stem (as a sterile linen thread), the oil extracted from the seeds, the dry ripe seeds, the linseed cakes, and the fresh flowering plant. Flaxseed oil is the richest plant source of fatty acids (30-45%) with the chief fatty acids being alpha-linolenic acid (40-70%), linoleic acid (10-25%), and oleic acid (13-30%). Flaxseed contains high concentrations of the lignan precursor secoisolariciresinol-diglycoside and about 25% protein; it also contains soluble and insoluble fiber. Flaxseed is used orally for chronic constipation, colon damage due to laxative abuse, diverticulitis, enteritis, gastritis, irritable colon, and hypercholesterolemia. Topical flaxseed preparations are used as poultices for burns, scalds, and other types of skin irritation. Germany's Commission E has approved flaxseed as a bulk laxative and as a topical poultice. In the US, flaxseed is regulated as an herbal dietary supplement and is not FDA-approved for any use. One product, Numoisyn liquid, contains sorbitol mixed with flaxseed (linseed) extract and it is formulated for the relief of chronic and temporary xerostomia (dry mouth). Flaxseed dietary supplements must not be confused with Denatured flaxseed or linseed oil is a component of paints and varnishes and is toxic to humans.
General Administration Information
For storage information, see the specific product information within the How Supplied section.
Route-Specific Administration
Oral Administration
Oral Solid Formulations
-Flaxseed: Available as whole, bruised, or milled seed for oral administration. Adequate amounts of fluids should be taken to prevent possible GI obstruction. The seeds may be also be incorporated into muffins or breads or given as encapsulated or loose powder. To prepare mucilage (gruel), use one tablespoonful of seeds to one cup or about 30-50 g of seeds to a liter. To prepare a decoction, simmer 15 g of whole seed in 1 cup water for 10-15 minutes.
-Flaxseed oil soft gels: Flaxseed oil is best absorbed when taken with food.
Oral Liquid Formulations
-Flaxseed oil: Flaxseed oil is best absorbed when taken with food. For maximum benefits, it is recommended that flaxseed oil be added to foods but not cooked or heated.
Topical Administration
-30-50 g of flaxseed flour is typically used as a hot moist poultice or compress.
When flaxseed is taken within recommended dosage ranges, there are no side effects with either the whole seeds, bruised seeds, flour, or oil. When flaxseed is taken as a nutritional supplement it may increase stool bulk and frequency. Patients taking flaxseed for bulk laxative effect may note the usual gassy or bloated feelings from increased dietary fiber intake. However, large doses taken without sufficient liquid can cause GI obstruction or ileus. Unspecified thyroid problems have also been reported. Chronic use or overuse of flaxseed may cause hypokalemia by promoting excessive potassium loss from the intestinal tract. Allergic and anaphylactoid reactions have been reported following ingestion of flaxseed products including: dyspnea, throat or chest tightness, chest pain (unspecified), urticaria, rash (unspecified), headache, pruritus, GI upset, and nausea. Also, hypersensitivity reactions may be more likely in workers processing flax products.
Flaxseed has not been evaluated by the Food and Drug Administration (FDA). Products containing flaxseed are not intended to diagnose, treat, cure, or prevent any disease. Consumers should also be informed that rigid quality control standards are not required for dietary supplements and substantial variability can occur in both the potency and the purity of these products.
Do not use flaxseed in patients who have demonstrated a previous hypersensitivity to flaxseed.
Some products made from flaxseed are not for human use or ingestion. Products labelled as flaxseed are for human consumption whereas products labelled 'linseed oil' are for industrial or craft use. Linseed oil can be very toxic. Patients should not take products made from flaxseed that are not labeled for use as nutritional supplements. If accidental exposure to such a product occurs, the patient should be instructed to contact a local poison control center and health care professional immediately.
Bulk-forming agents such as flaxseed fiber supplements are contraindicated in patients with acute abdomen, esophageal stricture or perforation, dysphagia, GI obstruction or ileus, acute intestinal inflammation, or unexplained abdominal pain. These precautions and contraindications do not apply to flaxseed oil capsules or to flaxseed oral solution.
Flaxseed oil has significant caloric content and should be used with caution in patients who are overweight or with clinical obesity. These people should use only the whole seeds which remain intact in the bowel without releasing the oil.
The German Commission E does not list pregnancy as a contraindication to flaxseed use. Animal data show that a lignan precursor, secoisolariciresinal, found in flaxseed oil has been demonstrated to affect fetal development. The estrogenic and anti-estrogenic effects are consistent with the mixed effects of lignan compounds. However, it is unknown what effect flaxseed would have on a developing human fetus. Flaxseed should be used with caution during pregnancy. Preferred alternatives for use in pregnancy for the purpose of constipation would include the use of psyllium fiber. Other artificial saliva products in place of Numoisyn liquid would be preferred duirng pregnancy, due to lack of systemic intake.
The German Commission E does not list lactation as a contraindication to flaxseed use. However, it is unknown if any absorbed components of flaxseed are excreted in human breast milk. Flaxseed should be used with caution during breast-feeding. Preferred alternatives for use during lactation for the purpose of constipation or increasing fiber intake would include the use of psyllium fiber. Other artificial saliva products in place of Numoisyn liquid would be preferred in a nursing mother, due to lack of systemic intake.
For chronic constipation*, colon damage due to laxative abuse*, diverticulitis*, enterocolitis*, irritable colon*:
Oral dosage:
Adults: The German Commission E recommends 1 tablespoon of whole or cracked (not ground) seed with 6 ounces (150 mL) of liquid PO 2-3 times per day. Alternatively, 10 g PO of whole or cracked (not ground) seed with meals and at least 6 ounces of liquid 2-3 times per day.
-for use as a mucilage for gastritis* and enteritis*:
Oral dosage:
Adults: 2-4 tablespoons of milled flaxseed for preparation of flaxseed gruel.
For use as a dietary supplement to reduce serum cholesterol in patients with hypercholesterolemia*:
Oral dosage:
Adults: 35-50 g PO daily of crushed seeds have been used.
Oral dosage (flaxseed oil):
Adults: 14 mL PO of flaxseed oil or 1-4 flaxseed oil softgels once or twice daily depending on the specific product.
For use as a poultice or compress for burns* and scalds*, local skin irritation*, drawing poultices for local infections*, pimples*, boils*, etc.:
Topical dosage:
Adults: The German Commission E recommends applying 30-50 g of flaxseed flour as a moist-heat poultice or compress.
For the treatment of chronic and temporary xerostomia:
Product contains sorbitol as the primary ingredient (see Saliva substitute monograph).
Oral and Oropharyngeal dosage:
Adults: Administer 2 mL PO as needed; instruct patient to rinse the solution around in mouth before swallowing.
Maximum Dosage Limits:
-Adults
Specific maximum dosage information is not available.
-Elderly
Specific maximum dosage information is not available.
-Adolescents
Safety and efficacy have not been established.
-Children
Safety and efficacy have not been established.
Patients with Hepatic Impairment Dosing
Flaxseed has not been evaluated in the presence of hepatic impairment. Specific guidelines for dosage adjustments are not available.
Patients with Renal Impairment Dosing
Flaxseed has not been evaluated in the presence of renal impairment. Specific guidelines for dosage adjustments are not available.
*non-FDA-approved indication
Digoxin: (Moderate) Flaxseed fiber can impair the absorption of oral drugs when administered concomitantly. However, no drug interaction studies have been performed to assess the degree to which the absorption of oral drugs may be altered. Based on interactions of other plant seed fiber (e.g., psyllium) used as a bulk-forming laxative, flaxseed fiber may adsorb cardiac glycosides. Administration of prescribed oral agents should be separated from the administration of flaxseed fiber by at least 2 hours.
Warfarin: (Moderate) Flaxseed fiber can impair the absorption of oral drugs when administered concomitantly. However, no drug interaction studies have been performed to assess the degree to which the absorption of oral drugs may be altered. Based on interactions of other plant seed fiber (e.g., psyllium) used as a bulk-forming laxative, flaxseed fiber may adsorb oral anticoagulants (e.g., warfarin). Administration of prescribed oral agents should be separated from the administration of flaxseed fiber by at least 2 hours.
Flaxseed is used as an antihyperlipidemic agent and as a bulk-forming laxative. It is also an indirect source of lignans (e.g., enterolactone, enterodiol) which are purported to have a variety of effects.
-Antihyperlipidemic effects: Flaxseed contains alpha-linolenic acid which is a precursor to certain omega-3 fatty acids. Omega-3 fatty acids lower LDL cholesterol and triglyceride levels. Omega-3 fatty acids also block over-aggregation of platelets, lower blood pressure in persons with hypertension, and lower fibrinogen levels, however, clinical data evaluating these effects in humans is equivocal or lacking.
-GI effects: The epidermis of the testa contains 3-6% mucilage which has a high swelling capacity. It absorbs water (up to 8 times its own weight) in the GI tract which causes swelling of the mucilage and expansion of the stool. The resultant bulk facilitates peristalsis and bowel motility. Additionally, the high mucilage content provides protection for mucous membranes of the GI tract. Theoretically, flaxseed may bind to toxic metabolites produced during digestion and may reduce bloat.
-Other effects: Flaxseed contains high concentrations of the lignan precursor secoisolariciresinol-diglycoside which is converted by bacteria in the colon to the lignans enterolactone and enterodiol. The content of these precursors in flaxseed can vary significantly depending on growing location and harvest year. The clinical role of lignans has not yet been defined. Weak estrogenic effects and possibly antiestrogenic effects have been reported. Lignans appear to compete with endogenous estrogen for estrogen binding sites, resulting in an antiestrogen effect which may lead to inhibition of the growth of hormone-dependent cancer cells. In vitro data reported inhibition of mammary and colon tumor growth by enterolactone and enterodial. Lignans may also have other beneficial effects such as platelet activating factor receptor antagonist activity and antioxidant effects. Inhibition of angiogenesis may also be possible.
Flaxseed has been administered orally and topically. Precise pharmacokinetic data are not currently available.
-Route-Specific Pharmacokinetics
Oral Route
One study reported that the bioavailability of alpha-linolenic acid from flaxseed and flaxseed powder may be as high as from flaxseed oil. The lignan precursor secoisolariciresinol-diglycoside contained in flaxseed is converted by bacteria in the colon to the lignans enterolactone and enterodiol. These lignans are absorbed from the colon and excreted in the urine in variable amounts.