Hi Melinda,
I just attended a lecture by Dr. Stephen Sager, who is a radiation oncologist who has done a lot of research in the area of complementary therapies. You may want to research information about his research.
Generally, we need to keep in mind that supplements - vitamins and otherwise, are not regulated by the government, so that you never really know what you buy off the shelf.
There is a reliable site which you may consult: http://nccam.nih.gov/health/
It is extensive. Some of the information it provides (through Medline) about flaxseed is the following.
Interactions with Drugs
Taking flaxseed ( not flaxseed oil) by mouth
may reduce the absorption of other medications. Drugs used by mouth should be
taken one hour before or two hours after flaxseed to prevent decreased
absorption. People taking mood stabilizers such as lithium should use caution.
Flaxseed contains alpha-linolenic acid, which may theoretically lower blood
pressure. Individuals taking medications to lower blood pressure should use
caution when taking flaxseed. Laxatives and stool softeners may increase or
enhance the laxative effects of flaxseed. Flaxseed and flaxseed oil can lower
cholesterol levels in animals, but studies in humans show mixed results. In
theory, flaxseed may increase the effect of other medications that lower lipid
(cholesterol and triglyceride) levels in the blood. Hormonal drugs may be
affected. Dietary flaxseed may increase the effects of tamoxifen, a medication
used to treat cancer. Consult a qualified oncologist and pharmacist before
making decisions about treatment or health conditions.
Although studies report conflicting results, the
omega-3 fatty acids in flaxseed and flaxseed oil may increase blood sugar,
reducing the effects of diabetes treatments, including insulin and
glucose-lowering medications taken by mouth. Flaxseed ( not flaxseed
oil) is a rich source of plant lignans. Lignans are sometimes referred to as
phytoestrogens and may possess estrogen-like properties. It is not known if
flaxseed can alter the effect of birth control pills or hormone replacement
therapies. Flaxseed and flaxseed oil theoretically may increase the risk of
bleeding, and caution should be used when flaxseed products are taken with drugs
that increase the risk of bleeding. Some examples include aspirin,
anticoagulants ("blood thinners") such as warfarin (Coumadin ® ) or
heparin, anti-platelet drugs such as clopidogrel (Plavix ® ), and
non-steroidal anti-inflammatory drugs such as ibuprofen (Motrin ® ,
Advil ® ) or naproxen (Naprosyn ® , Aleve ®).
---- just to alert that it is wise (i) to tell your oncologist of whatever you are planning to take and ask whether s/he is aware of any relevant research; and (ii) research any vitamin or other supplement before embarking on it.
Hope that helps.