Tamoxifen is an antiestrogen drug primarily used to treat women with breast cancer or possibly to help prevent breast cancer in women at high risk. It is also used to treat mastalgia (painful breasts) and gynecomastia (abnormal breast enlargement in males).
Summary of Interactions with Vitamins, Herbs, and Foods
In some cases, an herb or supplement may appear in more than one category, which may seem contradictory. For clarification, read the full article for details about the summarized interactions.
 May be Beneficial: Supportive interaction—Taking these supplements may support or otherwise help your medication work better. | Gamma linolenic acid (GLA) Melatonin* Tocotrienols* |
 Avoid: Adverse interaction—Avoid these supplements when taking this medication because taking them together may cause undesirable or dangerous results. | Citrus flavonoids (tangeretin) |
| Depletion or interference | None known |
| Side effect reduction/prevention | None known |
| Reduced drug absorption/bioavailability | None known |
An asterisk (*) next to an item in the summary indicates that the interaction is supported only by weak, fragmentary, and/or contradictory scientific evidence.
Interactions with Dietary Supplements
Citrus flavonoids
Preliminary research in animals found that the citrus flavonoid tangeretin (found primarily in the peel of citrus fruits) interferes with the ability of tamoxifen to inhibit tumor growth.1 Although the evidence is far from conclusive, people taking tamoxifen should probably avoid citrus bioflavonoid supplements, as well as beverages and foods to which citrus peel oils have been added.
Gamma-linolenic acid
Gamma-linolenic acid (GLA), found in evening primrose and borage oils, may enhance the therapeutic effects of tamoxifen. A small group of breast cancer patients took 2.8 g of oral GLA per day in addition to tamoxifen, in a preliminary trial.2 Another group of breast cancer patients took tamoxifen alone. Those taking the GLA-tamoxifen combination appeared to have a better clinical response than did those taking tamoxifen alone. However, the results of this preliminary research are far from conclusive and need to be confirmed in a larger, more definitive trial.
Melatonin
In preliminary research, large amounts of melatonin were used successfully in combination with tamoxifen in a few people with breast cancer for whom tamoxifen had previously failed.3 The amounts used in this study should be taken only under the supervision of a doctor.
Tocotrienols
Tocotrienols are compounds similar to vitamin E that are found in palm oil. Test tube studies have shown that tocotrienols enhance the effects of tamoxifen.4 Controlled studies are needed to determine whether supplementing with tocotrienols might enhance the anticancer effects of tamoxifen.
References
1. Bracke ME, Depypere HT, Boterberg T, et al. Influence of tangeretin on tamoxifen’s therapeutic benefit in mammary cancer. J Natl Cancer Inst 1999;91:354–9.
2. Kenny FS, Pinder SE, Ellis IO, et al. Gamma linolenic acid with tamoxifen as primary therapy in breast cancer. Int J Cancer 2000;85:643–8.
3. Lissoni P, Barni S, Meregalli S, et al. Modulation of cancer endocrine therapy by melatonin: A phase II study of tamoxifen plus melatonin in metastatic breast cancer patients progression under tamoxifen alone. Br J Cancer 1995;71:854–6.
4. Guthrie N, Gapor A, Chambers AF, Carroll KK. Inhibition of proliferation of estrogen receptor-negative MDA-MB-435 and -positive MCF-7 human breast cancer cells by palm oil tocotrienols and tamoxifen, alone and in combination. J Nutr 1997;127:544S–8S.
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2006-09-07
