Flaxseed (Linum usitatissimum) and flaxseed oil, which comes from flaxseed, are rich sources of the essential fatty acid alpha-linolenic acid — a heart-healthy omega-3 fatty acid. Flaxseed is high in soluble fiber and in lignans, which contain phytoestrogens. Similar to the hormone estrogen, phytoestrogens might have anti-cancer properties. Flaxseed oil doesn't have these phytoestrogens.

Flaxseed can be used whole or crushed, or in a powder form as meal or flour. Flaxseed oil is available in liquid and capsule form.

People use flaxseed and flaxseed oil to reduce cholesterol and blood sugar and treat digestive conditions. Some people also take flaxseed to treat inflammatory diseases.

Research on the use of flaxseed and flaxseed oil for specific conditions shows:

• Heart disease. Some studies suggest that alpha-linolenic acid, which is found in flaxseed and flaxseed oil, might benefit people with heart disease. Early research also suggests that flaxseed might help lower high blood pressure, which plays a role in heart disease.
• Cholesterol levels. Several studies show that taking flaxseed daily can reduce total cholesterol and low-density lipoprotein (LDL, or "bad") cholesterol levels. However, other studies aren't as favorable.
• Diabetes. Taking flaxseed might lower blood sugar levels in people with type 2 diabetes. However, the same results haven't been found for flaxseed oil.
• Menopausal symptoms. Results have been mixed when it comes to use of flaxseed and the treatment of menopausal symptoms.

When taken in recommended amounts, flaxseed and flaxseed oil are generally safe to use. However, when taken in large amounts and with too little water, flaxseed can cause:

• Bloating
• Gas
• Diarrhea

Avoid use of flaxseed and flaxseed oil during pregnancy.

Occasionally, using flaxseed or flaxseed oil causes an allergic reaction.

Don't eat raw or unripe flaxseeds.

Because flaxseed oil might decrease blood clotting, stop using flaxseed oil two weeks before having elective surgery.

The evidence is mixed as to whether flaxseed or flaxseed oil has any effect on the prostate or the risk of prostate cancer.

Possible interactions include:

• Anticoagulant and anti-platelet drugs, herbs and supplements. These types of drugs, herbs and supplements reduce blood clotting. Flaxseed oil also might decrease blood clotting. It's possible that taking flaxseed oil might increase the risk of bleeding.
• Blood pressure drugs, herbs and supplements. Flaxseed oil might lower blood pressure. Taking flaxseed oil with drugs, herbs and supplements that lower blood pressure might lower blood pressure too much.
• Diabetes drugs. Flaxseed might lower blood sugar levels. Taking flaxseed with diabetes drugs or herbs or supplements with hypoglycemic potential might lower blood sugar too much.
• Estrogens. Flaxseed might have an anti-estrogen effect. Taking flaxseed might decrease the effects of oral contraceptive drugs and estrogen replacement therapy.
• Oral drugs. Taking flaxseed might decrease absorption of oral drugs. Consider taking oral drugs and flaxseed an hour or two apart.