Cautions According To WebMD

Contra-Indications
Pregnancy: Taking flaxseed by mouth during pregnancy is possibly unsafe. Flaxseed can act like the hormone estrogen. Some healthcare providers worry that this might harm the pregnancy. But there is no reliable clinical evidence about its effects on pregnancy. Until more is known, stay on the safe side and avoid use.

Breast-feeding: There isn't enough reliable information to know if flaxseed is safe to use when breast-feeding. Stay on the safe side and avoid use.

Hormone-sensitive cancers or conditions: Because flaxseed might act somewhat like the hormone estrogen, it might make hormone-sensitive conditions worse. Some of these conditions include breast and ovarian cancer. Until more is known, avoid taking large amounts of flaxseed if you have one of these conditions.

High triglyceride levels (hypertriglyceridemia): Partially defatted flaxseed, which contains less alpha linolenic acid content, might increase triglyceride levels. If your triglyceride levels are too high, don't take this type of flaxseed.

Surgery: Flaxseed might increase the risk of bleeding during and after surgery. Stop using it at least 2 weeks before a scheduled surgery.

Possible Side Effects:
When taken by mouth: Flaxseed is likely safe for most adults. Adding flaxseed to the diet might increase the number of bowel movements each day. It might also cause side effects such as bloating, gas, stomachache, and nausea. Higher doses are likely to cause more side effects.

Taking flaxseed extracts that contain lignans is possibly safe. Flaxseed lignan extracts can be used safely for up to 6 months.

Taking raw or unripe flaxseed by mouth is possibly unsafe. It might be poisonous.

When applied to the skin: Flaxseed is possibly safe when used in a cloth on the skin.

Possible Interactions:
Moderate Interaction Be cautious with this combination

Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs) interacts with Flaxseed.
Flaxseed might slow blood clotting. Taking flaxseed along with medications that also slow blood clotting might increase the risk of bruising and bleeding.

Medications for diabetes (Antidiabetes drugs) interacts with Flaxseed
Flaxseed might lower blood sugar levels. Taking flaxseed along with diabetes medications might cause blood sugar to drop too low. Monitor your blood sugar closely.

Medications for high blood pressure (Antihypertensive drugs) interacts with Flaxseed
Flaxseed might lower blood pressure. Taking flaxseed along with medications that lower blood pressure might cause blood pressure to go too low. Monitor your blood pressure closely.

Antibiotic drugs interacts with Flaxseed
Bacteria in the intestine convert some of the chemicals in flaxseed into lignans, which are thought to be responsible for many of the possible benefits of flaxseed. However, because antibiotics kill these bacteria, lignans might not be formed as usual. This might alter the effects of flaxseed.

Estrogens interacts with Flaxseed
Flaxseed can act like the female hormone estrogen. It might compete with drugs that contain estrogen. Flaxseed might make these estrogen-containing drugs less effective.