Overview

Flaxseed is commonly used for various reasons, including heart health, diabetes, gut health, and menopause, but its benefits are not well defined. Whole or ground flaxseed is added to many foods. Flaxseed, flaxseed oil, and flaxseed extracts are also available over-the-counter as dietary supplements. Common side effects include bloating, fullness, constipation, loose stools, or gas. Before taking flaxseed, make sure to tell your health care provider about any health conditions you have or medicines you are taking.

Uses

What is flaxseed used for?

Flaxseed products are used for many different reasons. However, their benefits are not well defined. Some common reasons that people use flaxseed products include the following.

• Constipation
• Diabetes
• High cholesterol
• Menopause symptoms
• Weight loss
• To boost the immune system

Note: The FDA has not reviewed flaxseed for safety and effectiveness. Learn more about dietary supplements here.

How does flaxseed work (mechanism of action)?

Flaxseed, sometimes called linseed, is the seed of the flax plant, which is called Linum usitatissimum. Whole and ground flaxseed, as well as the oil from flaxseed, are commonly added to foods. Flaxseed, flaxseed oil, and flaxseed extract are also available as dietary supplements.

Flaxseed contains large amounts of insoluble fiber. This is a type of fiber that is not absorbed by your body. Instead, it stays in your gut and helps soften your stools and make them more regular, which can help with constipation. Insoluble fiber also slows down how quickly your body absorbs the sugars in the foods that you eat. But it is not clear if flaxseed can help lower blood sugar levels in people with diabetes.

Flaxseed also contains omega-3 fatty acids. Flaxseed oil, which comes from flaxseed, is made almost entirely of omega-3 fatty acids. One of the most common fatty acids in flaxseed oil is alpha-linolenic acid (ALA). Omega-3 fatty acids have many important functions in your eyes, brain, heart, blood vessels, and immune system. They can also help reduce swelling (inflammation). But the benefits of flaxseed or flaxseed oil for heart and immune system health are not well defined.

Flaxseed also contains chemicals called lignans. One of the main lignans in flaxseed is called secoisolariciresinol diglycoside (SDG). Lignans act like antioxidants in your body and may also have estrogen-like effects. This has led to interest in using them for cancer and menopause. But the benefits of flaxseed lignans for menopause symptoms and hormone-sensitive cancers are not well defined.

Herbal products like flaxseed naturally contain many different substances, including fiber, fatty acids, and lignans. The amounts of each substance in a specific flaxseed product may vary. Some, none, or all of these substances may have effects on the body. These effects may change depending on how much of each substance is found in the product you are using.

How should I store flaxseed?

You should store flaxseed according to the product label. Most dietary supplements should be kept in a cool, dry location that is out of the reach of children and pets and not in direct sunlight.

Side Effects

What are the most common side effects of flaxseed?

The most common side effects of flaxseed are listed below. These side effects may vary depending on the dose you are taking or the product you are using. Tell your health care provider if you have any of these side effects that bother you.

• Bloating or fullness
• Loose stools or constipation
• Gas

There may be other side effects of flaxseed that are not listed here. Contact your health care provider if you think you are having a side effect of a supplement. In the U.S., you can report side effects to the FDA at www.safetyreporting.hhs.gov or by calling 888-SAFEFOOD (888-723-3366). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of flaxseed?

While less common, the most serious side effects of flaxseed are described below, along with what to do if they happen.

Severe Allergic Reactions. Flaxseed may cause allergic reactions, which can be serious. Stop taking flaxseed and get help right away if you have any of the following symptoms of a serious allergic reaction.

• Breathing problems or wheezing
• Racing heart
• Fever or general ill feeling
• Swollen lymph nodes
• Swelling of the face, lips, mouth, tongue, or throat
• Trouble swallowing or throat tightness
• Itching or skin rash
• Bumps on the skin called hives, which can be red, pink, white, or brown depending on your skin tone
• Nausea or vomiting
• Dizziness, feeling lightheaded, or fainting
• Stomach cramps
• Joint pain

Precautions

Who should not use flaxseed?

Allergies to Ingredients. People who are allergic to any of the following should not take flaxseed.

• Flax
• Flaxseed
• Flaxseed oil
• Linseed
• Linum usitatissimum
• Any of the ingredients in the specific product

Your pharmacist can tell you all of the ingredients in the specific flaxseed products they stock.

What should I know about flaxseed before using it?

Flaxseed is available as a food and as a dietary supplement. It cannot be marketed to treat or cure a disease.

Read and follow the directions on the specific product you are taking, or take it as recommended by your health care provider.

Keep flaxseed out of the reach of children.

Ground flaxseed contains large amounts of fiber. Adding a large amount of fiber to your diet all at once may increase your risk of stomach or gut discomfort. If you are adding flaxseed to your diet, start with small amounts each day and slowly increase the amount every few days. Adding flaxseed to a meal can also help reduce your risk of side effects. It is also important to make sure you are drinking enough fluid each day.

Raw flaxseed can cause serious side effects. You should only eat flaxseeds that have been cooked. Flaxseed dietary supplements contain cooked, ground flaxseed.

Herbal products, such as flaxseed, naturally contain many different substances. The amount of each substance in a specific flaxseed product can change for many reasons, including the area where the plant was grown, the weather during growth, the time of year when it was harvested, and the way the seeds were processed after they were harvested. If you switch to a new bottle or a different brand, you may not have the same effects or side effects because of this variability. Talk to your health care provider if you have questions or concerns.

Flaxseed is available in many different forms, including whole or ground flaxseed, flaxseed oil, and flaxseed lignan extract. Whole or ground flaxseeds contain omega-3 fatty acids, fiber, and lignans. Each of these substances can have effects on the body. Flaxseed oil products contain large amounts of omega-3 fatty acids. Flaxseed lignan extracts contain large amounts of lignans. Each of these different products can have very different effects on the body.

The FDA has not tested flaxseed dietary supplement products to confirm that they contain the ingredients stated on their labels. Some dietary supplements have been tested by third-party organizations to confirm that they contain the ingredients listed on their labels and do not contain any harmful chemicals. Learn more about how to choose a safe dietary supplement product here.

What should I tell my health care provider before using flaxseed?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if flaxseed is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions.Tell your health care provider if you have any of the following.

• Bleeding problems
• Hormone-sensitive cancer, such as breast, uterine, or ovarian cancer

Other Medicines and Supplements.Flaxseed may interact with other medicines and supplements. Before taking flaxseed, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how flaxseed could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. Flaxseed passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does flaxseed interact with foods or drinks?

There are no known interactions between flaxseed and foods or drinks. Taking flaxseed or flaxseed oil with food may reduce your risk of side effects.

It is unknown if drinking alcohol will affect flaxseed.

Does flaxseed interact with medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking flaxseed.

• A blood thinner, which is a medicine used to treat or prevent blood clots
• An antiplatelet medicine, such as aspirin/dipyridamole, cilostazol, clopidogrel (Plavix), or ticagrelor (Brilinta), which is a medicine used to prevent blood clots

The interactions between flaxseed and medicines are not fully understood. As with most dietary supplements, the research on drug interactions with flaxseed is incomplete. Always check with your health care provider before taking flaxseed with any medicines.

Dosing

What should I do if I accidentally use too much flaxseed?

If you or someone else has used too much flaxseed, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

Flaxseed and flaxseed oil are found in many foods and can also be added to foods. Flaxseed dietary supplements may contain whole flaxseed, flaxseed oil, or flaxseed lignan extract. Read the product label closely and speak with a health care provider about how to take flaxseed products safely. Do not take double or extra doses, even if you miss a dose.