Keith I. Block, M.D. follow us read our blog

Ask Dr. Block

Flaxseed during Breast Cancer Treatment

Question: Does flaxseed interact with Aromasin and similar medications?

Answer: Aromasin, Arimidex and Femara are all medications called “aromatase inhibitors.” They are used in breast cancer treatment for women who are post-menopausal and whose tumors are stimulated to grow by estrogen (estrogen-receptor positive or ER+ breast cancer). They are generally prescribed after patients have completed their surgery, radiation and/or chemotherapy.

In my opinion, the studies indicating that flax has no significant phytoestrogenic effect in humans are more convincing than the ones indicating that it might stimulate estrogens. This implies that flaxseed would not interact with aromatase inhibitors due to phytoestrogenic activity. However, there is a concern that should be addressed; that is, flax has laxative effects because of its high fiber content. This could result in medications that are taken by mouth being sped out of the digestive system too quickly to dissolve completely. The solution to this is relatively simple: take the oral medications one hour before or two hours after taking flaxseed supplements. This applies to ground flaxseed, which is quite fibrous, and not flaxseed oil, which, of course, has the fiber removed. And since flax can provide a number of other health benefits, including moderating inflammation, which may be important with breast cancer, you could consider taking flax for these reasons.

Therefore, from a practical perspective, I am fine with my patients consuming cracked flax either added to a breakfast cereal or in muffins and cookies. It does provide healthy omega 3 fatty acids with a clinically beneficial anti-inflammatory effect. However, though I believe there are benefits and that they even now outweigh any genuine downsides, the impact on estrogen is still not yet fully resolved. So while I support the use of flax, I would not yet promote flax as the next superfood.

For a more in depth discussion of this topic including references, read the full article: