Flaxseed and its derivative flaxseed oil (or linseed oil) are rich sources of the essential fatty acid alpha-linolenic acid (ALA), which is a biologic precursor to omega-3 fatty acids such as eicosapentaenoic acid. Although omega-3 fatty acids have been associated with improved cardiovascular outcomes, evidence from human trials is mixed regarding the efficacy of flaxseed products for coronary artery disease or hyperlipidemia (high lipid levels).
The lignans of flaxseed (not flaxseed oil) possess in vitro antioxidant and estrogen-like properties, prompting theories about their efficacy for the treatment of breast cancer. However, there is not sufficient human evidence to make a strong conclusion. As a source of fiber, flaxseed (not flaxseed oil) taken by mouth possesses laxative properties. In large doses, or when taken with inadequate water, flaxseed may cause bowel obstruction. The effects of flaxseed on blood glucose levels are not clear, although hyperglycemic (increased blood sugar) effects have been reported with omega-3 fatty acids in general.
Flaxseed oil contains only the ALA component of flaxseed and not the fiber or lignan components. Therefore, flaxseed oil may share the purported lipid-lowering properties of flaxseed but not its proposed laxative or anticancer abilities.
NB! The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.
Adults (18 years and older)
Flaxseed oil is most often taken by mouth in a liquid form, which contains approximately seven grams of alpha-linolenic acid (ALA) and approximately 130 calories per 15-milliliter tablespoon.
Flaxseed oil capsules (one or two grams) have been taken by mouth daily for 180 days.
Flaxseed flour (30-100 grams) may be mixed with water to form a moist compress and applied to the skin three times daily.
A single whole flaxseed has been placed under the eyelid to allow a foreign body or mucus to adhere to it, thereby facilitating removal from the eye. This process may be unsafe, and it is suggested that a healthcare professional be consulted for removal of foreign bodies from the eye.
- For benign prostatic hypertrophy (BPH), 300 and 600 milligrams of a flaxseed lignan extract have been taken by mouth daily for four months.
- For breast cancer, 5-25 grams daily has been taken by mouth for up to four months.
- For cyclic mastalgia, flax muffins or baked products, with flax contents of 25-50 grams, are commonly taken by mouth in clinical trials for up to six months.
- For diabetes, flax muffins or baked products, with flax contents of 25-50 grams, are commonly taken by mouth in clinical trials for up to six months.
- For gastritis or enteritis, one tablespoon of whole or bruised flaxseed mixed with 150 milliliters of liquid has been taken by mouth 2-3 times daily.
- For hyperlipidemia, flax muffins or baked products, with flax contents of 25-50 grams, are commonly taken by mouth in clinical trials for up to six months.
- As a laxative, 2-3 tablespoons of bulk flaxseed mixed in 10 times the amount of water have been taken by mouth; 45 grams daily has also been used.
- For menopausal symptoms, 5-25 grams has been taken by mouth daily for up to four months; 40 grams of flaxseed has also been taken by mouth daily.
- For lupus nephritis, 30 grams of flaxseed has been taken by mouth daily.
- For obesity, 30 grams of flaxseed flour has been taken by mouth daily for two weeks.
Children (under 18 years old)
For attention-deficit hyperactivity disorder (ADHD), flax oil (200 milligrams of ALA content), along with 25 milligrams of vitamin C, has been taken by mouth twice daily for three months.
NB! There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
Avoid with a known allergy or hypersensitivity to flaxseed ( Linum usitatissimum ), flaxseed oil, its constituents, or any other members of the Linaceae plant family. Hypersensitivity reactions to flaxseed following occupational exposure have been reported. Diarrhea; intestinal and abdominal pain; itching, including itchy palms and soles and itchy, weeping eyes; hives; malaise; nasal obstruction; nausea; shortness of breath; sneezing; vomiting; and watery discharge have been reported.
Side Effects and Warnings
Flaxseed may cause gastrointestinal symptoms, headache, “heart problems,” hives, increased red blood cell counts, increased risk of prostate cancer, intestinal obstruction, mania or hypomania (in bipolar patients), prolonged luteal phases, rapid breathing, respiratory disease (in flax farmers), vomiting, and weight gain or weight loss. An overdose of flaxseed or flaxseed oil may result in weakness, unstable gait, paralysis, or seizures.
- Raw flaxseed or flaxseed plant may increase blood levels of cyanide, a toxic chemical.
- Flaxseed may cause low blood pressure. Caution is advised in patients with blood pressure disorders and those taking drugs, herbs, or supplements that affect blood pressure.
- Based on the available evidence, flaxseed, which contains alpha-linolenic acid (ALA), should be avoided in patients with prostate cancer or those at risk for prostate cancer.
- Use flaxseed and flaxseed oil cautiously in patients with elevated triglycerides, as these agents may raise or lower triglyceride levels.
- Flaxseed may increase the risk of bleeding and bleeding time. Caution is advised in patients with bleeding disorders or those taking drugs, herbs, or supplements that may increase the risk of bleeding. Dosing adjustments may be necessary.
- Flaxseed may lower blood sugar levels. Caution is advised in patients with diabetes or low blood sugar, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.
- Use cautiously in patients using laxatives, as flaxseed, particularly at higher doses (more than 30 grams daily), caused loose stools; theoretically, concurrent use may increase the risk of diarrhea.
- Use cautiously in patients using furosemide or ketoprofen, as flaxseed decreased the absorption of these drugs.
- Because flaxseed contains estrogen-like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.
- Use flaxseed (not flaxseed oil) cautiously in women with hormone-sensitive conditions, due to its possible estrogenic properties.
- Avoid consumption of immature flaxseed seedpods, as they may be poisonous.
- Avoid topical flaxseed on open wounds or abraded surfaces.
- Avoid flaxseed (not flaxseed oil) in patients with esophageal stricture, ileus, gastrointestinal stricture, or bowel obstruction. Ingestion of flaxseed without adequate fluids may precipitate bowel obstruction.
- Avoid in patients with acute or chronic diarrhea, irritable bowel disease, diverticulitis (small, bulging sacs or pouches of the inner lining of the intestine that become inflamed or infected), or inflammatory bowel disease, due to the potential laxative effect of flaxseed.
- Some natural medicine textbooks advise caution in patients with hypothyroidism, although scant clinical data exist in this area.
- Avoid in pregnant or breastfeeding women, due to a lack of available scientific evidence and safety information.
- Avoid with a known allergy or hypersensitivity to flaxseed (Linum usitatissimum), flaxseed oil, their constituents, or any other members of the Linaceae plant family. Hypersensitivity reactions to flaxseed following occupational exposure have been reported. Diarrhea; intense general malaise; intestinal and abdominal pain; itching, including itchy palms and soles and itchy, weeping eyes; hives; nasal obstruction; nausea; shortness of breath; sneezing; vomiting; and watery discharge have been reported.
Pregnancy and Breastfeeding
Avoid in pregnant or breastfeeding women, due to a lack of available scientific evidence and safety information.