Warnings and precautions to be aware of concerning the safety of flaxseed include the following:
- Because flaxseed is high in fiber, it could cause problems in people with a bowel obstruction or esophageal stricture. If you have either of these problems, it is probably best to avoid flaxseed.
- Make sure to take flaxseed with plenty of water. Taking flaxseed dry could be dangerous, as it can swell in the esophagus, possibly causing a blockage.
- Flaxseed may have estrogen-like effects and could theoretically worsen some hormone-sensitive cancers. If you have cancer (or a history of cancer), check with your healthcare provider before taking flaxseed medicinally (although eating it in normal food amounts is probably okay).
- Theoretically, high doses of flaxseed could increase the risk of bleeding. This is especially important for people who are already at risk for bleeding, such as those with a bleeding disorder.
- Like any other fiber, flaxseed may increase the risk of low blood sugar in people who are taking diabetes medications, especially if they are not accustomed to consuming much fiber. If you have diabetes, monitor your blood sugar closely when starting flaxseed (or when increasing your intake).
- One type of flaxseed, known as defatted flaxseed, may increase triglycerides. If you have high triglycerides, you should choose flaxseed that has not been defatted.
- Flaxseed can interact with some medications (see Flaxseed Drug Interactions for more information).
- Flaxseed is probably safe for pregnant or breastfeeding women when taken in normal food amounts (see Flaxseed and Pregnancy and Flaxseed and Breastfeeding).