Flaxseed is the seed of the flax plant, which is believed to have originated in Egypt. It grows throughout Canada and the northwestern United States. Flaxseed oil comes from flaxseeds.

• Flaxseed is most commonly used as a laxative.
• Flaxseed is also used for hot flashes and breast pain.
• Flaxseed oil is used for different conditions than flaxseed, including arthritis.
• Both flaxseed and flaxseed oil have been used for high cholesterol levels and in an effort to prevent cancer.

Whole or crushed flaxseed can be mixed with water or juice and taken by mouth. Flaxseed is also available in powder form. Flaxseed oil is available in liquid and capsule form. Flaxseed contains lignans (phytoestrogens, or plant estrogens), while flaxseed oil preparations lack lignans.

What the Science Says

• Flaxseed contains soluble fiber, like that found in oat bran, and is an effective laxative.
• Studies of flaxseed preparations to lower cholesterol levels report mixed results.
• Some studies suggest that alpha-linolenic acid (a substance found in flaxseed and flaxseed oil) may benefit people with heart disease. But not enough reliable data are available to determine whether flaxseed is effective for heart conditions.
• Study results are mixed on whether flaxseed decreases hot flashes.
• NCCAM is funding studies on flaxseed. Recent studies have looked at the effects of flaxseed on high cholesterol levels, as well as its possible role in preventing conditions such as heart disease and osteoporosis.

Side Effects and Cautions

• Flaxseed and flaxseed oil supplements seem to be well tolerated. Few side effects have been reported.
• Flaxseed, like any supplemental fiber source, should be taken with plenty of water; otherwise, it could worsen constipation or, in rare cases, even cause intestinal blockage.
• The fiber in flaxseed may lower the body's ability to absorb medications that are taken by mouth. Flaxseed should not be taken at the same time as any conventional oral medications or other dietary supplements.
• Tell your health care providers about any complementary and alternative practices you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.