Although no toxicity has been reported, conflicting information exists about the effects of the oil and the ALA fatty acid that it contains on cancer risk. Because of these conflicting reports, it is suggested that one of the side effects of flax seed oil may be an increased risk of breast cancer. Even a study on prostate cancer shows the same conflicting information, so it is difficult to determine if flax seed oil includes an increased cancer risk as one of the side effects of flax seed oil.

One thing it is important to keep in mind is that although flax seed oil is a good source of dietary fiber in addition to being a good source of Omega-3 essential fatty acids, it is not intended to be used for cooking nor should it be taken by anyone who has an intestinal obstruction. This is true not just of flax seed oil but any source of fiber and people who suffer from systemic sclerosis may develop side effects of flax seed oil such as severe constipation or bowel obstruction that requires hospitalization.

Although not yet proven, another one of the potential side effects of flax seed oil is that large amounts consumed during pregnancy may adversely affect the development of the reproductive system. This study was conducted on animals, and has not yet been researched in humans. For the safety of both mother and baby, until tests are conclusive, it is best to stay away from flax seed oil during pregnancy and nursing.

Although an excellent source of dietary fiber, it is important to keep in mind potential risk for those who do suffer from intestinal problems and do not use this supplement without doctor approval. For all others, it is an excellent source of fiber and fatty acids that are essential for a body's well-being.